Abseil Common Libraries (C++) (grcp 依赖)
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2751 lines
111 KiB
2751 lines
111 KiB
// Copyright 2017 The Abseil Authors. |
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// |
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// Licensed under the Apache License, Version 2.0 (the "License"); |
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// you may not use this file except in compliance with the License. |
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// You may obtain a copy of the License at |
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// |
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// https://www.apache.org/licenses/LICENSE-2.0 |
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// |
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// Unless required by applicable law or agreed to in writing, software |
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// distributed under the License is distributed on an "AS IS" BASIS, |
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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// See the License for the specific language governing permissions and |
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// limitations under the License. |
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#include "absl/synchronization/mutex.h" |
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#ifdef _WIN32 |
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#include <windows.h> |
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#ifdef ERROR |
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#undef ERROR |
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#endif |
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#else |
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#include <fcntl.h> |
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#include <pthread.h> |
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#include <sched.h> |
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#include <sys/time.h> |
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#endif |
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#include <assert.h> |
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#include <errno.h> |
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#include <stdio.h> |
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#include <stdlib.h> |
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#include <string.h> |
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#include <time.h> |
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#include <algorithm> |
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#include <atomic> |
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#include <cinttypes> |
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#include <thread> // NOLINT(build/c++11) |
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#include "absl/base/attributes.h" |
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#include "absl/base/call_once.h" |
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#include "absl/base/config.h" |
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#include "absl/base/dynamic_annotations.h" |
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#include "absl/base/internal/atomic_hook.h" |
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#include "absl/base/internal/cycleclock.h" |
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#include "absl/base/internal/hide_ptr.h" |
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#include "absl/base/internal/low_level_alloc.h" |
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#include "absl/base/internal/raw_logging.h" |
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#include "absl/base/internal/spinlock.h" |
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#include "absl/base/internal/sysinfo.h" |
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#include "absl/base/internal/thread_identity.h" |
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#include "absl/base/internal/tsan_mutex_interface.h" |
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#include "absl/base/port.h" |
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#include "absl/debugging/stacktrace.h" |
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#include "absl/debugging/symbolize.h" |
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#include "absl/synchronization/internal/graphcycles.h" |
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#include "absl/synchronization/internal/per_thread_sem.h" |
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#include "absl/time/time.h" |
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using absl::base_internal::CurrentThreadIdentityIfPresent; |
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using absl::base_internal::PerThreadSynch; |
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using absl::base_internal::SchedulingGuard; |
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using absl::base_internal::ThreadIdentity; |
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using absl::synchronization_internal::GetOrCreateCurrentThreadIdentity; |
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using absl::synchronization_internal::GraphCycles; |
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using absl::synchronization_internal::GraphId; |
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using absl::synchronization_internal::InvalidGraphId; |
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using absl::synchronization_internal::KernelTimeout; |
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using absl::synchronization_internal::PerThreadSem; |
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extern "C" { |
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ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalMutexYield)() { |
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std::this_thread::yield(); |
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} |
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} // extern "C" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace { |
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#if defined(ABSL_HAVE_THREAD_SANITIZER) |
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constexpr OnDeadlockCycle kDeadlockDetectionDefault = OnDeadlockCycle::kIgnore; |
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#else |
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constexpr OnDeadlockCycle kDeadlockDetectionDefault = OnDeadlockCycle::kAbort; |
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#endif |
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ABSL_CONST_INIT std::atomic<OnDeadlockCycle> synch_deadlock_detection( |
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kDeadlockDetectionDefault); |
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ABSL_CONST_INIT std::atomic<bool> synch_check_invariants(false); |
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ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES |
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absl::base_internal::AtomicHook<void (*)(int64_t wait_cycles)> |
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submit_profile_data; |
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ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES absl::base_internal::AtomicHook<void (*)( |
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const char *msg, const void *obj, int64_t wait_cycles)> |
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mutex_tracer; |
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ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES |
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absl::base_internal::AtomicHook<void (*)(const char *msg, const void *cv)> |
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cond_var_tracer; |
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ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES absl::base_internal::AtomicHook< |
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bool (*)(const void *pc, char *out, int out_size)> |
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symbolizer(absl::Symbolize); |
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} // namespace |
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static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu, |
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bool locking, bool trylock, |
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bool read_lock); |
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void RegisterMutexProfiler(void (*fn)(int64_t wait_timestamp)) { |
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submit_profile_data.Store(fn); |
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} |
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void RegisterMutexTracer(void (*fn)(const char *msg, const void *obj, |
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int64_t wait_cycles)) { |
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mutex_tracer.Store(fn); |
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} |
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void RegisterCondVarTracer(void (*fn)(const char *msg, const void *cv)) { |
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cond_var_tracer.Store(fn); |
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} |
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void RegisterSymbolizer(bool (*fn)(const void *pc, char *out, int out_size)) { |
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symbolizer.Store(fn); |
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} |
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namespace { |
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// Represents the strategy for spin and yield. |
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// See the comment in GetMutexGlobals() for more information. |
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enum DelayMode { AGGRESSIVE, GENTLE }; |
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struct ABSL_CACHELINE_ALIGNED MutexGlobals { |
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absl::once_flag once; |
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int spinloop_iterations = 0; |
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int32_t mutex_sleep_limit[2] = {}; |
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}; |
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const MutexGlobals &GetMutexGlobals() { |
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ABSL_CONST_INIT static MutexGlobals data; |
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absl::base_internal::LowLevelCallOnce(&data.once, [&]() { |
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const int num_cpus = absl::base_internal::NumCPUs(); |
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data.spinloop_iterations = num_cpus > 1 ? 1500 : 0; |
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// If this a uniprocessor, only yield/sleep. Otherwise, if the mode is |
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// aggressive then spin many times before yielding. If the mode is |
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// gentle then spin only a few times before yielding. Aggressive spinning |
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// is used to ensure that an Unlock() call, which must get the spin lock |
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// for any thread to make progress gets it without undue delay. |
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if (num_cpus > 1) { |
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data.mutex_sleep_limit[AGGRESSIVE] = 5000; |
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data.mutex_sleep_limit[GENTLE] = 250; |
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} else { |
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data.mutex_sleep_limit[AGGRESSIVE] = 0; |
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data.mutex_sleep_limit[GENTLE] = 0; |
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} |
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}); |
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return data; |
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} |
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} // namespace |
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namespace synchronization_internal { |
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// Returns the Mutex delay on iteration `c` depending on the given `mode`. |
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// The returned value should be used as `c` for the next call to `MutexDelay`. |
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int MutexDelay(int32_t c, int mode) { |
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const int32_t limit = GetMutexGlobals().mutex_sleep_limit[mode]; |
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if (c < limit) { |
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// Spin. |
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c++; |
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} else { |
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SchedulingGuard::ScopedEnable enable_rescheduling; |
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ABSL_TSAN_MUTEX_PRE_DIVERT(nullptr, 0); |
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if (c == limit) { |
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// Yield once. |
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ABSL_INTERNAL_C_SYMBOL(AbslInternalMutexYield)(); |
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c++; |
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} else { |
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// Then wait. |
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absl::SleepFor(absl::Microseconds(10)); |
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c = 0; |
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} |
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ABSL_TSAN_MUTEX_POST_DIVERT(nullptr, 0); |
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} |
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return c; |
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} |
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} // namespace synchronization_internal |
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// --------------------------Generic atomic ops |
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// Ensure that "(*pv & bits) == bits" by doing an atomic update of "*pv" to |
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// "*pv | bits" if necessary. Wait until (*pv & wait_until_clear)==0 |
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// before making any change. |
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// This is used to set flags in mutex and condition variable words. |
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static void AtomicSetBits(std::atomic<intptr_t>* pv, intptr_t bits, |
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intptr_t wait_until_clear) { |
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intptr_t v; |
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do { |
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v = pv->load(std::memory_order_relaxed); |
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} while ((v & bits) != bits && |
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((v & wait_until_clear) != 0 || |
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!pv->compare_exchange_weak(v, v | bits, |
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std::memory_order_release, |
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std::memory_order_relaxed))); |
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} |
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// Ensure that "(*pv & bits) == 0" by doing an atomic update of "*pv" to |
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// "*pv & ~bits" if necessary. Wait until (*pv & wait_until_clear)==0 |
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// before making any change. |
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// This is used to unset flags in mutex and condition variable words. |
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static void AtomicClearBits(std::atomic<intptr_t>* pv, intptr_t bits, |
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intptr_t wait_until_clear) { |
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intptr_t v; |
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do { |
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v = pv->load(std::memory_order_relaxed); |
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} while ((v & bits) != 0 && |
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((v & wait_until_clear) != 0 || |
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!pv->compare_exchange_weak(v, v & ~bits, |
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std::memory_order_release, |
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std::memory_order_relaxed))); |
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} |
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//------------------------------------------------------------------ |
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// Data for doing deadlock detection. |
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ABSL_CONST_INIT static absl::base_internal::SpinLock deadlock_graph_mu( |
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absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY); |
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// Graph used to detect deadlocks. |
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ABSL_CONST_INIT static GraphCycles *deadlock_graph |
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ABSL_GUARDED_BY(deadlock_graph_mu) ABSL_PT_GUARDED_BY(deadlock_graph_mu); |
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//------------------------------------------------------------------ |
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// An event mechanism for debugging mutex use. |
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// It also allows mutexes to be given names for those who can't handle |
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// addresses, and instead like to give their data structures names like |
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// "Henry", "Fido", or "Rupert IV, King of Yondavia". |
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namespace { // to prevent name pollution |
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enum { // Mutex and CondVar events passed as "ev" to PostSynchEvent |
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// Mutex events |
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SYNCH_EV_TRYLOCK_SUCCESS, |
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SYNCH_EV_TRYLOCK_FAILED, |
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SYNCH_EV_READERTRYLOCK_SUCCESS, |
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SYNCH_EV_READERTRYLOCK_FAILED, |
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SYNCH_EV_LOCK, |
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SYNCH_EV_LOCK_RETURNING, |
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SYNCH_EV_READERLOCK, |
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SYNCH_EV_READERLOCK_RETURNING, |
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SYNCH_EV_UNLOCK, |
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SYNCH_EV_READERUNLOCK, |
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// CondVar events |
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SYNCH_EV_WAIT, |
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SYNCH_EV_WAIT_RETURNING, |
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SYNCH_EV_SIGNAL, |
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SYNCH_EV_SIGNALALL, |
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}; |
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enum { // Event flags |
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SYNCH_F_R = 0x01, // reader event |
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SYNCH_F_LCK = 0x02, // PostSynchEvent called with mutex held |
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SYNCH_F_TRY = 0x04, // TryLock or ReaderTryLock |
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SYNCH_F_UNLOCK = 0x08, // Unlock or ReaderUnlock |
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SYNCH_F_LCK_W = SYNCH_F_LCK, |
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SYNCH_F_LCK_R = SYNCH_F_LCK | SYNCH_F_R, |
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}; |
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} // anonymous namespace |
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// Properties of the events. |
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static const struct { |
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int flags; |
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const char *msg; |
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} event_properties[] = { |
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{SYNCH_F_LCK_W | SYNCH_F_TRY, "TryLock succeeded "}, |
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{0, "TryLock failed "}, |
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{SYNCH_F_LCK_R | SYNCH_F_TRY, "ReaderTryLock succeeded "}, |
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{0, "ReaderTryLock failed "}, |
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{0, "Lock blocking "}, |
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{SYNCH_F_LCK_W, "Lock returning "}, |
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{0, "ReaderLock blocking "}, |
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{SYNCH_F_LCK_R, "ReaderLock returning "}, |
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{SYNCH_F_LCK_W | SYNCH_F_UNLOCK, "Unlock "}, |
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{SYNCH_F_LCK_R | SYNCH_F_UNLOCK, "ReaderUnlock "}, |
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{0, "Wait on "}, |
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{0, "Wait unblocked "}, |
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{0, "Signal on "}, |
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{0, "SignalAll on "}, |
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}; |
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ABSL_CONST_INIT static absl::base_internal::SpinLock synch_event_mu( |
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absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY); |
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// Hash table size; should be prime > 2. |
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// Can't be too small, as it's used for deadlock detection information. |
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static constexpr uint32_t kNSynchEvent = 1031; |
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static struct SynchEvent { // this is a trivial hash table for the events |
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// struct is freed when refcount reaches 0 |
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int refcount ABSL_GUARDED_BY(synch_event_mu); |
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// buckets have linear, 0-terminated chains |
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SynchEvent *next ABSL_GUARDED_BY(synch_event_mu); |
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// Constant after initialization |
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uintptr_t masked_addr; // object at this address is called "name" |
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// No explicit synchronization used. Instead we assume that the |
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// client who enables/disables invariants/logging on a Mutex does so |
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// while the Mutex is not being concurrently accessed by others. |
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void (*invariant)(void *arg); // called on each event |
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void *arg; // first arg to (*invariant)() |
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bool log; // logging turned on |
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// Constant after initialization |
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char name[1]; // actually longer---NUL-terminated string |
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} * synch_event[kNSynchEvent] ABSL_GUARDED_BY(synch_event_mu); |
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// Ensure that the object at "addr" has a SynchEvent struct associated with it, |
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// set "bits" in the word there (waiting until lockbit is clear before doing |
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// so), and return a refcounted reference that will remain valid until |
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// UnrefSynchEvent() is called. If a new SynchEvent is allocated, |
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// the string name is copied into it. |
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// When used with a mutex, the caller should also ensure that kMuEvent |
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// is set in the mutex word, and similarly for condition variables and kCVEvent. |
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static SynchEvent *EnsureSynchEvent(std::atomic<intptr_t> *addr, |
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const char *name, intptr_t bits, |
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intptr_t lockbit) { |
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uint32_t h = reinterpret_cast<intptr_t>(addr) % kNSynchEvent; |
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SynchEvent *e; |
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// first look for existing SynchEvent struct.. |
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synch_event_mu.Lock(); |
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for (e = synch_event[h]; |
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e != nullptr && e->masked_addr != base_internal::HidePtr(addr); |
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e = e->next) { |
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} |
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if (e == nullptr) { // no SynchEvent struct found; make one. |
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if (name == nullptr) { |
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name = ""; |
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} |
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size_t l = strlen(name); |
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e = reinterpret_cast<SynchEvent *>( |
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base_internal::LowLevelAlloc::Alloc(sizeof(*e) + l)); |
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e->refcount = 2; // one for return value, one for linked list |
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e->masked_addr = base_internal::HidePtr(addr); |
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e->invariant = nullptr; |
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e->arg = nullptr; |
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e->log = false; |
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strcpy(e->name, name); // NOLINT(runtime/printf) |
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e->next = synch_event[h]; |
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AtomicSetBits(addr, bits, lockbit); |
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synch_event[h] = e; |
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} else { |
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e->refcount++; // for return value |
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} |
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synch_event_mu.Unlock(); |
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return e; |
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} |
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// Deallocate the SynchEvent *e, whose refcount has fallen to zero. |
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static void DeleteSynchEvent(SynchEvent *e) { |
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base_internal::LowLevelAlloc::Free(e); |
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} |
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// Decrement the reference count of *e, or do nothing if e==null. |
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static void UnrefSynchEvent(SynchEvent *e) { |
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if (e != nullptr) { |
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synch_event_mu.Lock(); |
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bool del = (--(e->refcount) == 0); |
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synch_event_mu.Unlock(); |
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if (del) { |
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DeleteSynchEvent(e); |
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} |
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} |
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} |
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// Forget the mapping from the object (Mutex or CondVar) at address addr |
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// to SynchEvent object, and clear "bits" in its word (waiting until lockbit |
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// is clear before doing so). |
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static void ForgetSynchEvent(std::atomic<intptr_t> *addr, intptr_t bits, |
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intptr_t lockbit) { |
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uint32_t h = reinterpret_cast<intptr_t>(addr) % kNSynchEvent; |
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SynchEvent **pe; |
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SynchEvent *e; |
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synch_event_mu.Lock(); |
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for (pe = &synch_event[h]; |
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(e = *pe) != nullptr && e->masked_addr != base_internal::HidePtr(addr); |
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pe = &e->next) { |
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} |
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bool del = false; |
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if (e != nullptr) { |
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*pe = e->next; |
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del = (--(e->refcount) == 0); |
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} |
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AtomicClearBits(addr, bits, lockbit); |
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synch_event_mu.Unlock(); |
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if (del) { |
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DeleteSynchEvent(e); |
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} |
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} |
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// Return a refcounted reference to the SynchEvent of the object at address |
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// "addr", if any. The pointer returned is valid until the UnrefSynchEvent() is |
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// called. |
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static SynchEvent *GetSynchEvent(const void *addr) { |
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uint32_t h = reinterpret_cast<intptr_t>(addr) % kNSynchEvent; |
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SynchEvent *e; |
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synch_event_mu.Lock(); |
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for (e = synch_event[h]; |
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e != nullptr && e->masked_addr != base_internal::HidePtr(addr); |
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e = e->next) { |
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} |
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if (e != nullptr) { |
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e->refcount++; |
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} |
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synch_event_mu.Unlock(); |
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return e; |
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} |
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// Called when an event "ev" occurs on a Mutex of CondVar "obj" |
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// if event recording is on |
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static void PostSynchEvent(void *obj, int ev) { |
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SynchEvent *e = GetSynchEvent(obj); |
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// logging is on if event recording is on and either there's no event struct, |
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// or it explicitly says to log |
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if (e == nullptr || e->log) { |
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void *pcs[40]; |
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int n = absl::GetStackTrace(pcs, ABSL_ARRAYSIZE(pcs), 1); |
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// A buffer with enough space for the ASCII for all the PCs, even on a |
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// 64-bit machine. |
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char buffer[ABSL_ARRAYSIZE(pcs) * 24]; |
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int pos = snprintf(buffer, sizeof (buffer), " @"); |
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for (int i = 0; i != n; i++) { |
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pos += snprintf(&buffer[pos], sizeof (buffer) - pos, " %p", pcs[i]); |
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} |
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ABSL_RAW_LOG(INFO, "%s%p %s %s", event_properties[ev].msg, obj, |
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(e == nullptr ? "" : e->name), buffer); |
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} |
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const int flags = event_properties[ev].flags; |
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if ((flags & SYNCH_F_LCK) != 0 && e != nullptr && e->invariant != nullptr) { |
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// Calling the invariant as is causes problems under ThreadSanitizer. |
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// We are currently inside of Mutex Lock/Unlock and are ignoring all |
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// memory accesses and synchronization. If the invariant transitively |
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// synchronizes something else and we ignore the synchronization, we will |
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// get false positive race reports later. |
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// Reuse EvalConditionAnnotated to properly call into user code. |
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struct local { |
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static bool pred(SynchEvent *ev) { |
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(*ev->invariant)(ev->arg); |
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return false; |
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} |
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}; |
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Condition cond(&local::pred, e); |
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Mutex *mu = static_cast<Mutex *>(obj); |
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const bool locking = (flags & SYNCH_F_UNLOCK) == 0; |
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const bool trylock = (flags & SYNCH_F_TRY) != 0; |
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const bool read_lock = (flags & SYNCH_F_R) != 0; |
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EvalConditionAnnotated(&cond, mu, locking, trylock, read_lock); |
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} |
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UnrefSynchEvent(e); |
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} |
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//------------------------------------------------------------------ |
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// The SynchWaitParams struct encapsulates the way in which a thread is waiting: |
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// whether it has a timeout, the condition, exclusive/shared, and whether a |
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// condition variable wait has an associated Mutex (as opposed to another |
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// type of lock). It also points to the PerThreadSynch struct of its thread. |
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// cv_word tells Enqueue() to enqueue on a CondVar using CondVarEnqueue(). |
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// |
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// This structure is held on the stack rather than directly in |
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// PerThreadSynch because a thread can be waiting on multiple Mutexes if, |
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// while waiting on one Mutex, the implementation calls a client callback |
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// (such as a Condition function) that acquires another Mutex. We don't |
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// strictly need to allow this, but programmers become confused if we do not |
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// allow them to use functions such a LOG() within Condition functions. The |
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// PerThreadSynch struct points at the most recent SynchWaitParams struct when |
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// the thread is on a Mutex's waiter queue. |
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struct SynchWaitParams { |
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SynchWaitParams(Mutex::MuHow how_arg, const Condition *cond_arg, |
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KernelTimeout timeout_arg, Mutex *cvmu_arg, |
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PerThreadSynch *thread_arg, |
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std::atomic<intptr_t> *cv_word_arg) |
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: how(how_arg), |
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cond(cond_arg), |
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timeout(timeout_arg), |
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cvmu(cvmu_arg), |
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thread(thread_arg), |
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cv_word(cv_word_arg), |
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contention_start_cycles(base_internal::CycleClock::Now()) {} |
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const Mutex::MuHow how; // How this thread needs to wait. |
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const Condition *cond; // The condition that this thread is waiting for. |
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// In Mutex, this field is set to zero if a timeout |
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// expires. |
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KernelTimeout timeout; // timeout expiry---absolute time |
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// In Mutex, this field is set to zero if a timeout |
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// expires. |
|
Mutex *const cvmu; // used for transfer from cond var to mutex |
|
PerThreadSynch *const thread; // thread that is waiting |
|
|
|
// If not null, thread should be enqueued on the CondVar whose state |
|
// word is cv_word instead of queueing normally on the Mutex. |
|
std::atomic<intptr_t> *cv_word; |
|
|
|
int64_t contention_start_cycles; // Time (in cycles) when this thread started |
|
// to contend for the mutex. |
|
}; |
|
|
|
struct SynchLocksHeld { |
|
int n; // number of valid entries in locks[] |
|
bool overflow; // true iff we overflowed the array at some point |
|
struct { |
|
Mutex *mu; // lock acquired |
|
int32_t count; // times acquired |
|
GraphId id; // deadlock_graph id of acquired lock |
|
} locks[40]; |
|
// If a thread overfills the array during deadlock detection, we |
|
// continue, discarding information as needed. If no overflow has |
|
// taken place, we can provide more error checking, such as |
|
// detecting when a thread releases a lock it does not hold. |
|
}; |
|
|
|
// A sentinel value in lists that is not 0. |
|
// A 0 value is used to mean "not on a list". |
|
static PerThreadSynch *const kPerThreadSynchNull = |
|
reinterpret_cast<PerThreadSynch *>(1); |
|
|
|
static SynchLocksHeld *LocksHeldAlloc() { |
|
SynchLocksHeld *ret = reinterpret_cast<SynchLocksHeld *>( |
|
base_internal::LowLevelAlloc::Alloc(sizeof(SynchLocksHeld))); |
|
ret->n = 0; |
|
ret->overflow = false; |
|
return ret; |
|
} |
|
|
|
// Return the PerThreadSynch-struct for this thread. |
|
static PerThreadSynch *Synch_GetPerThread() { |
|
ThreadIdentity *identity = GetOrCreateCurrentThreadIdentity(); |
|
return &identity->per_thread_synch; |
|
} |
|
|
|
static PerThreadSynch *Synch_GetPerThreadAnnotated(Mutex *mu) { |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0); |
|
} |
|
PerThreadSynch *w = Synch_GetPerThread(); |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0); |
|
} |
|
return w; |
|
} |
|
|
|
static SynchLocksHeld *Synch_GetAllLocks() { |
|
PerThreadSynch *s = Synch_GetPerThread(); |
|
if (s->all_locks == nullptr) { |
|
s->all_locks = LocksHeldAlloc(); // Freed by ReclaimThreadIdentity. |
|
} |
|
return s->all_locks; |
|
} |
|
|
|
// Post on "w"'s associated PerThreadSem. |
|
inline void Mutex::IncrementSynchSem(Mutex *mu, PerThreadSynch *w) { |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0); |
|
} |
|
PerThreadSem::Post(w->thread_identity()); |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0); |
|
} |
|
} |
|
|
|
// Wait on "w"'s associated PerThreadSem; returns false if timeout expired. |
|
bool Mutex::DecrementSynchSem(Mutex *mu, PerThreadSynch *w, KernelTimeout t) { |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0); |
|
} |
|
assert(w == Synch_GetPerThread()); |
|
static_cast<void>(w); |
|
bool res = PerThreadSem::Wait(t); |
|
if (mu) { |
|
ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0); |
|
} |
|
return res; |
|
} |
|
|
|
// We're in a fatal signal handler that hopes to use Mutex and to get |
|
// lucky by not deadlocking. We try to improve its chances of success |
|
// by effectively disabling some of the consistency checks. This will |
|
// prevent certain ABSL_RAW_CHECK() statements from being triggered when |
|
// re-rentry is detected. The ABSL_RAW_CHECK() statements are those in the |
|
// Mutex code checking that the "waitp" field has not been reused. |
|
void Mutex::InternalAttemptToUseMutexInFatalSignalHandler() { |
|
// Fix the per-thread state only if it exists. |
|
ThreadIdentity *identity = CurrentThreadIdentityIfPresent(); |
|
if (identity != nullptr) { |
|
identity->per_thread_synch.suppress_fatal_errors = true; |
|
} |
|
// Don't do deadlock detection when we are already failing. |
|
synch_deadlock_detection.store(OnDeadlockCycle::kIgnore, |
|
std::memory_order_release); |
|
} |
|
|
|
// --------------------------time support |
|
|
|
// Return the current time plus the timeout. Use the same clock as |
|
// PerThreadSem::Wait() for consistency. Unfortunately, we don't have |
|
// such a choice when a deadline is given directly. |
|
static absl::Time DeadlineFromTimeout(absl::Duration timeout) { |
|
#ifndef _WIN32 |
|
struct timeval tv; |
|
gettimeofday(&tv, nullptr); |
|
return absl::TimeFromTimeval(tv) + timeout; |
|
#else |
|
return absl::Now() + timeout; |
|
#endif |
|
} |
|
|
|
// --------------------------Mutexes |
|
|
|
// In the layout below, the msb of the bottom byte is currently unused. Also, |
|
// the following constraints were considered in choosing the layout: |
|
// o Both the debug allocator's "uninitialized" and "freed" patterns (0xab and |
|
// 0xcd) are illegal: reader and writer lock both held. |
|
// o kMuWriter and kMuEvent should exceed kMuDesig and kMuWait, to enable the |
|
// bit-twiddling trick in Mutex::Unlock(). |
|
// o kMuWriter / kMuReader == kMuWrWait / kMuWait, |
|
// to enable the bit-twiddling trick in CheckForMutexCorruption(). |
|
static const intptr_t kMuReader = 0x0001L; // a reader holds the lock |
|
static const intptr_t kMuDesig = 0x0002L; // there's a designated waker |
|
static const intptr_t kMuWait = 0x0004L; // threads are waiting |
|
static const intptr_t kMuWriter = 0x0008L; // a writer holds the lock |
|
static const intptr_t kMuEvent = 0x0010L; // record this mutex's events |
|
// INVARIANT1: there's a thread that was blocked on the mutex, is |
|
// no longer, yet has not yet acquired the mutex. If there's a |
|
// designated waker, all threads can avoid taking the slow path in |
|
// unlock because the designated waker will subsequently acquire |
|
// the lock and wake someone. To maintain INVARIANT1 the bit is |
|
// set when a thread is unblocked(INV1a), and threads that were |
|
// unblocked reset the bit when they either acquire or re-block |
|
// (INV1b). |
|
static const intptr_t kMuWrWait = 0x0020L; // runnable writer is waiting |
|
// for a reader |
|
static const intptr_t kMuSpin = 0x0040L; // spinlock protects wait list |
|
static const intptr_t kMuLow = 0x00ffL; // mask all mutex bits |
|
static const intptr_t kMuHigh = ~kMuLow; // mask pointer/reader count |
|
|
|
// Hack to make constant values available to gdb pretty printer |
|
enum { |
|
kGdbMuSpin = kMuSpin, |
|
kGdbMuEvent = kMuEvent, |
|
kGdbMuWait = kMuWait, |
|
kGdbMuWriter = kMuWriter, |
|
kGdbMuDesig = kMuDesig, |
|
kGdbMuWrWait = kMuWrWait, |
|
kGdbMuReader = kMuReader, |
|
kGdbMuLow = kMuLow, |
|
}; |
|
|
|
// kMuWrWait implies kMuWait. |
|
// kMuReader and kMuWriter are mutually exclusive. |
|
// If kMuReader is zero, there are no readers. |
|
// Otherwise, if kMuWait is zero, the high order bits contain a count of the |
|
// number of readers. Otherwise, the reader count is held in |
|
// PerThreadSynch::readers of the most recently queued waiter, again in the |
|
// bits above kMuLow. |
|
static const intptr_t kMuOne = 0x0100; // a count of one reader |
|
|
|
// flags passed to Enqueue and LockSlow{,WithTimeout,Loop} |
|
static const int kMuHasBlocked = 0x01; // already blocked (MUST == 1) |
|
static const int kMuIsCond = 0x02; // conditional waiter (CV or Condition) |
|
|
|
static_assert(PerThreadSynch::kAlignment > kMuLow, |
|
"PerThreadSynch::kAlignment must be greater than kMuLow"); |
|
|
|
// This struct contains various bitmasks to be used in |
|
// acquiring and releasing a mutex in a particular mode. |
|
struct MuHowS { |
|
// if all the bits in fast_need_zero are zero, the lock can be acquired by |
|
// adding fast_add and oring fast_or. The bit kMuDesig should be reset iff |
|
// this is the designated waker. |
|
intptr_t fast_need_zero; |
|
intptr_t fast_or; |
|
intptr_t fast_add; |
|
|
|
intptr_t slow_need_zero; // fast_need_zero with events (e.g. logging) |
|
|
|
intptr_t slow_inc_need_zero; // if all the bits in slow_inc_need_zero are |
|
// zero a reader can acquire a read share by |
|
// setting the reader bit and incrementing |
|
// the reader count (in last waiter since |
|
// we're now slow-path). kMuWrWait be may |
|
// be ignored if we already waited once. |
|
}; |
|
|
|
static const MuHowS kSharedS = { |
|
// shared or read lock |
|
kMuWriter | kMuWait | kMuEvent, // fast_need_zero |
|
kMuReader, // fast_or |
|
kMuOne, // fast_add |
|
kMuWriter | kMuWait, // slow_need_zero |
|
kMuSpin | kMuWriter | kMuWrWait, // slow_inc_need_zero |
|
}; |
|
static const MuHowS kExclusiveS = { |
|
// exclusive or write lock |
|
kMuWriter | kMuReader | kMuEvent, // fast_need_zero |
|
kMuWriter, // fast_or |
|
0, // fast_add |
|
kMuWriter | kMuReader, // slow_need_zero |
|
~static_cast<intptr_t>(0), // slow_inc_need_zero |
|
}; |
|
static const Mutex::MuHow kShared = &kSharedS; // shared lock |
|
static const Mutex::MuHow kExclusive = &kExclusiveS; // exclusive lock |
|
|
|
#ifdef NDEBUG |
|
static constexpr bool kDebugMode = false; |
|
#else |
|
static constexpr bool kDebugMode = true; |
|
#endif |
|
|
|
#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE |
|
static unsigned TsanFlags(Mutex::MuHow how) { |
|
return how == kShared ? __tsan_mutex_read_lock : 0; |
|
} |
|
#endif |
|
|
|
static bool DebugOnlyIsExiting() { |
|
return false; |
|
} |
|
|
|
Mutex::~Mutex() { |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
if ((v & kMuEvent) != 0 && !DebugOnlyIsExiting()) { |
|
ForgetSynchEvent(&this->mu_, kMuEvent, kMuSpin); |
|
} |
|
if (kDebugMode) { |
|
this->ForgetDeadlockInfo(); |
|
} |
|
ABSL_TSAN_MUTEX_DESTROY(this, __tsan_mutex_not_static); |
|
} |
|
|
|
void Mutex::EnableDebugLog(const char *name) { |
|
SynchEvent *e = EnsureSynchEvent(&this->mu_, name, kMuEvent, kMuSpin); |
|
e->log = true; |
|
UnrefSynchEvent(e); |
|
} |
|
|
|
void EnableMutexInvariantDebugging(bool enabled) { |
|
synch_check_invariants.store(enabled, std::memory_order_release); |
|
} |
|
|
|
void Mutex::EnableInvariantDebugging(void (*invariant)(void *), |
|
void *arg) { |
|
if (synch_check_invariants.load(std::memory_order_acquire) && |
|
invariant != nullptr) { |
|
SynchEvent *e = EnsureSynchEvent(&this->mu_, nullptr, kMuEvent, kMuSpin); |
|
e->invariant = invariant; |
|
e->arg = arg; |
|
UnrefSynchEvent(e); |
|
} |
|
} |
|
|
|
void SetMutexDeadlockDetectionMode(OnDeadlockCycle mode) { |
|
synch_deadlock_detection.store(mode, std::memory_order_release); |
|
} |
|
|
|
// Return true iff threads x and y are part of the same equivalence |
|
// class of waiters. An equivalence class is defined as the set of |
|
// waiters with the same condition, type of lock, and thread priority. |
|
// |
|
// Requires that x and y be waiting on the same Mutex queue. |
|
static bool MuEquivalentWaiter(PerThreadSynch *x, PerThreadSynch *y) { |
|
return x->waitp->how == y->waitp->how && x->priority == y->priority && |
|
Condition::GuaranteedEqual(x->waitp->cond, y->waitp->cond); |
|
} |
|
|
|
// Given the contents of a mutex word containing a PerThreadSynch pointer, |
|
// return the pointer. |
|
static inline PerThreadSynch *GetPerThreadSynch(intptr_t v) { |
|
return reinterpret_cast<PerThreadSynch *>(v & kMuHigh); |
|
} |
|
|
|
// The next several routines maintain the per-thread next and skip fields |
|
// used in the Mutex waiter queue. |
|
// The queue is a circular singly-linked list, of which the "head" is the |
|
// last element, and head->next if the first element. |
|
// The skip field has the invariant: |
|
// For thread x, x->skip is one of: |
|
// - invalid (iff x is not in a Mutex wait queue), |
|
// - null, or |
|
// - a pointer to a distinct thread waiting later in the same Mutex queue |
|
// such that all threads in [x, x->skip] have the same condition, priority |
|
// and lock type (MuEquivalentWaiter() is true for all pairs in [x, |
|
// x->skip]). |
|
// In addition, if x->skip is valid, (x->may_skip || x->skip == null) |
|
// |
|
// By the spec of MuEquivalentWaiter(), it is not necessary when removing the |
|
// first runnable thread y from the front a Mutex queue to adjust the skip |
|
// field of another thread x because if x->skip==y, x->skip must (have) become |
|
// invalid before y is removed. The function TryRemove can remove a specified |
|
// thread from an arbitrary position in the queue whether runnable or not, so |
|
// it fixes up skip fields that would otherwise be left dangling. |
|
// The statement |
|
// if (x->may_skip && MuEquivalentWaiter(x, x->next)) { x->skip = x->next; } |
|
// maintains the invariant provided x is not the last waiter in a Mutex queue |
|
// The statement |
|
// if (x->skip != null) { x->skip = x->skip->skip; } |
|
// maintains the invariant. |
|
|
|
// Returns the last thread y in a mutex waiter queue such that all threads in |
|
// [x, y] inclusive share the same condition. Sets skip fields of some threads |
|
// in that range to optimize future evaluation of Skip() on x values in |
|
// the range. Requires thread x is in a mutex waiter queue. |
|
// The locking is unusual. Skip() is called under these conditions: |
|
// - spinlock is held in call from Enqueue(), with maybe_unlocking == false |
|
// - Mutex is held in call from UnlockSlow() by last unlocker, with |
|
// maybe_unlocking == true |
|
// - both Mutex and spinlock are held in call from DequeueAllWakeable() (from |
|
// UnlockSlow()) and TryRemove() |
|
// These cases are mutually exclusive, so Skip() never runs concurrently |
|
// with itself on the same Mutex. The skip chain is used in these other places |
|
// that cannot occur concurrently: |
|
// - FixSkip() (from TryRemove()) - spinlock and Mutex are held) |
|
// - Dequeue() (with spinlock and Mutex held) |
|
// - UnlockSlow() (with spinlock and Mutex held) |
|
// A more complex case is Enqueue() |
|
// - Enqueue() (with spinlock held and maybe_unlocking == false) |
|
// This is the first case in which Skip is called, above. |
|
// - Enqueue() (without spinlock held; but queue is empty and being freshly |
|
// formed) |
|
// - Enqueue() (with spinlock held and maybe_unlocking == true) |
|
// The first case has mutual exclusion, and the second isolation through |
|
// working on an otherwise unreachable data structure. |
|
// In the last case, Enqueue() is required to change no skip/next pointers |
|
// except those in the added node and the former "head" node. This implies |
|
// that the new node is added after head, and so must be the new head or the |
|
// new front of the queue. |
|
static PerThreadSynch *Skip(PerThreadSynch *x) { |
|
PerThreadSynch *x0 = nullptr; |
|
PerThreadSynch *x1 = x; |
|
PerThreadSynch *x2 = x->skip; |
|
if (x2 != nullptr) { |
|
// Each iteration attempts to advance sequence (x0,x1,x2) to next sequence |
|
// such that x1 == x0->skip && x2 == x1->skip |
|
while ((x0 = x1, x1 = x2, x2 = x2->skip) != nullptr) { |
|
x0->skip = x2; // short-circuit skip from x0 to x2 |
|
} |
|
x->skip = x1; // short-circuit skip from x to result |
|
} |
|
return x1; |
|
} |
|
|
|
// "ancestor" appears before "to_be_removed" in the same Mutex waiter queue. |
|
// The latter is going to be removed out of order, because of a timeout. |
|
// Check whether "ancestor" has a skip field pointing to "to_be_removed", |
|
// and fix it if it does. |
|
static void FixSkip(PerThreadSynch *ancestor, PerThreadSynch *to_be_removed) { |
|
if (ancestor->skip == to_be_removed) { // ancestor->skip left dangling |
|
if (to_be_removed->skip != nullptr) { |
|
ancestor->skip = to_be_removed->skip; // can skip past to_be_removed |
|
} else if (ancestor->next != to_be_removed) { // they are not adjacent |
|
ancestor->skip = ancestor->next; // can skip one past ancestor |
|
} else { |
|
ancestor->skip = nullptr; // can't skip at all |
|
} |
|
} |
|
} |
|
|
|
static void CondVarEnqueue(SynchWaitParams *waitp); |
|
|
|
// Enqueue thread "waitp->thread" on a waiter queue. |
|
// Called with mutex spinlock held if head != nullptr |
|
// If head==nullptr and waitp->cv_word==nullptr, then Enqueue() is |
|
// idempotent; it alters no state associated with the existing (empty) |
|
// queue. |
|
// |
|
// If waitp->cv_word == nullptr, queue the thread at either the front or |
|
// the end (according to its priority) of the circular mutex waiter queue whose |
|
// head is "head", and return the new head. mu is the previous mutex state, |
|
// which contains the reader count (perhaps adjusted for the operation in |
|
// progress) if the list was empty and a read lock held, and the holder hint if |
|
// the list was empty and a write lock held. (flags & kMuIsCond) indicates |
|
// whether this thread was transferred from a CondVar or is waiting for a |
|
// non-trivial condition. In this case, Enqueue() never returns nullptr |
|
// |
|
// If waitp->cv_word != nullptr, CondVarEnqueue() is called, and "head" is |
|
// returned. This mechanism is used by CondVar to queue a thread on the |
|
// condition variable queue instead of the mutex queue in implementing Wait(). |
|
// In this case, Enqueue() can return nullptr (if head==nullptr). |
|
static PerThreadSynch *Enqueue(PerThreadSynch *head, |
|
SynchWaitParams *waitp, intptr_t mu, int flags) { |
|
// If we have been given a cv_word, call CondVarEnqueue() and return |
|
// the previous head of the Mutex waiter queue. |
|
if (waitp->cv_word != nullptr) { |
|
CondVarEnqueue(waitp); |
|
return head; |
|
} |
|
|
|
PerThreadSynch *s = waitp->thread; |
|
ABSL_RAW_CHECK( |
|
s->waitp == nullptr || // normal case |
|
s->waitp == waitp || // Fer()---transfer from condition variable |
|
s->suppress_fatal_errors, |
|
"detected illegal recursion into Mutex code"); |
|
s->waitp = waitp; |
|
s->skip = nullptr; // maintain skip invariant (see above) |
|
s->may_skip = true; // always true on entering queue |
|
s->wake = false; // not being woken |
|
s->cond_waiter = ((flags & kMuIsCond) != 0); |
|
if (head == nullptr) { // s is the only waiter |
|
s->next = s; // it's the only entry in the cycle |
|
s->readers = mu; // reader count is from mu word |
|
s->maybe_unlocking = false; // no one is searching an empty list |
|
head = s; // s is new head |
|
} else { |
|
PerThreadSynch *enqueue_after = nullptr; // we'll put s after this element |
|
#ifdef ABSL_HAVE_PTHREAD_GETSCHEDPARAM |
|
int64_t now_cycles = base_internal::CycleClock::Now(); |
|
if (s->next_priority_read_cycles < now_cycles) { |
|
// Every so often, update our idea of the thread's priority. |
|
// pthread_getschedparam() is 5% of the block/wakeup time; |
|
// base_internal::CycleClock::Now() is 0.5%. |
|
int policy; |
|
struct sched_param param; |
|
const int err = pthread_getschedparam(pthread_self(), &policy, ¶m); |
|
if (err != 0) { |
|
ABSL_RAW_LOG(ERROR, "pthread_getschedparam failed: %d", err); |
|
} else { |
|
s->priority = param.sched_priority; |
|
s->next_priority_read_cycles = |
|
now_cycles + |
|
static_cast<int64_t>(base_internal::CycleClock::Frequency()); |
|
} |
|
} |
|
if (s->priority > head->priority) { // s's priority is above head's |
|
// try to put s in priority-fifo order, or failing that at the front. |
|
if (!head->maybe_unlocking) { |
|
// No unlocker can be scanning the queue, so we can insert into the |
|
// middle of the queue. |
|
// |
|
// Within a skip chain, all waiters have the same priority, so we can |
|
// skip forward through the chains until we find one with a lower |
|
// priority than the waiter to be enqueued. |
|
PerThreadSynch *advance_to = head; // next value of enqueue_after |
|
do { |
|
enqueue_after = advance_to; |
|
// (side-effect: optimizes skip chain) |
|
advance_to = Skip(enqueue_after->next); |
|
} while (s->priority <= advance_to->priority); |
|
// termination guaranteed because s->priority > head->priority |
|
// and head is the end of a skip chain |
|
} else if (waitp->how == kExclusive && |
|
Condition::GuaranteedEqual(waitp->cond, nullptr)) { |
|
// An unlocker could be scanning the queue, but we know it will recheck |
|
// the queue front for writers that have no condition, which is what s |
|
// is, so an insert at front is safe. |
|
enqueue_after = head; // add after head, at front |
|
} |
|
} |
|
#endif |
|
if (enqueue_after != nullptr) { |
|
s->next = enqueue_after->next; |
|
enqueue_after->next = s; |
|
|
|
// enqueue_after can be: head, Skip(...), or cur. |
|
// The first two imply enqueue_after->skip == nullptr, and |
|
// the last is used only if MuEquivalentWaiter(s, cur). |
|
// We require this because clearing enqueue_after->skip |
|
// is impossible; enqueue_after's predecessors might also |
|
// incorrectly skip over s if we were to allow other |
|
// insertion points. |
|
ABSL_RAW_CHECK(enqueue_after->skip == nullptr || |
|
MuEquivalentWaiter(enqueue_after, s), |
|
"Mutex Enqueue failure"); |
|
|
|
if (enqueue_after != head && enqueue_after->may_skip && |
|
MuEquivalentWaiter(enqueue_after, enqueue_after->next)) { |
|
// enqueue_after can skip to its new successor, s |
|
enqueue_after->skip = enqueue_after->next; |
|
} |
|
if (MuEquivalentWaiter(s, s->next)) { // s->may_skip is known to be true |
|
s->skip = s->next; // s may skip to its successor |
|
} |
|
} else { // enqueue not done any other way, so |
|
// we're inserting s at the back |
|
// s will become new head; copy data from head into it |
|
s->next = head->next; // add s after head |
|
head->next = s; |
|
s->readers = head->readers; // reader count is from previous head |
|
s->maybe_unlocking = head->maybe_unlocking; // same for unlock hint |
|
if (head->may_skip && MuEquivalentWaiter(head, s)) { |
|
// head now has successor; may skip |
|
head->skip = s; |
|
} |
|
head = s; // s is new head |
|
} |
|
} |
|
s->state.store(PerThreadSynch::kQueued, std::memory_order_relaxed); |
|
return head; |
|
} |
|
|
|
// Dequeue the successor pw->next of thread pw from the Mutex waiter queue |
|
// whose last element is head. The new head element is returned, or null |
|
// if the list is made empty. |
|
// Dequeue is called with both spinlock and Mutex held. |
|
static PerThreadSynch *Dequeue(PerThreadSynch *head, PerThreadSynch *pw) { |
|
PerThreadSynch *w = pw->next; |
|
pw->next = w->next; // snip w out of list |
|
if (head == w) { // we removed the head |
|
head = (pw == w) ? nullptr : pw; // either emptied list, or pw is new head |
|
} else if (pw != head && MuEquivalentWaiter(pw, pw->next)) { |
|
// pw can skip to its new successor |
|
if (pw->next->skip != |
|
nullptr) { // either skip to its successors skip target |
|
pw->skip = pw->next->skip; |
|
} else { // or to pw's successor |
|
pw->skip = pw->next; |
|
} |
|
} |
|
return head; |
|
} |
|
|
|
// Traverse the elements [ pw->next, h] of the circular list whose last element |
|
// is head. |
|
// Remove all elements with wake==true and place them in the |
|
// singly-linked list wake_list in the order found. Assumes that |
|
// there is only one such element if the element has how == kExclusive. |
|
// Return the new head. |
|
static PerThreadSynch *DequeueAllWakeable(PerThreadSynch *head, |
|
PerThreadSynch *pw, |
|
PerThreadSynch **wake_tail) { |
|
PerThreadSynch *orig_h = head; |
|
PerThreadSynch *w = pw->next; |
|
bool skipped = false; |
|
do { |
|
if (w->wake) { // remove this element |
|
ABSL_RAW_CHECK(pw->skip == nullptr, "bad skip in DequeueAllWakeable"); |
|
// we're removing pw's successor so either pw->skip is zero or we should |
|
// already have removed pw since if pw->skip!=null, pw has the same |
|
// condition as w. |
|
head = Dequeue(head, pw); |
|
w->next = *wake_tail; // keep list terminated |
|
*wake_tail = w; // add w to wake_list; |
|
wake_tail = &w->next; // next addition to end |
|
if (w->waitp->how == kExclusive) { // wake at most 1 writer |
|
break; |
|
} |
|
} else { // not waking this one; skip |
|
pw = Skip(w); // skip as much as possible |
|
skipped = true; |
|
} |
|
w = pw->next; |
|
// We want to stop processing after we've considered the original head, |
|
// orig_h. We can't test for w==orig_h in the loop because w may skip over |
|
// it; we are guaranteed only that w's predecessor will not skip over |
|
// orig_h. When we've considered orig_h, either we've processed it and |
|
// removed it (so orig_h != head), or we considered it and skipped it (so |
|
// skipped==true && pw == head because skipping from head always skips by |
|
// just one, leaving pw pointing at head). So we want to |
|
// continue the loop with the negation of that expression. |
|
} while (orig_h == head && (pw != head || !skipped)); |
|
return head; |
|
} |
|
|
|
// Try to remove thread s from the list of waiters on this mutex. |
|
// Does nothing if s is not on the waiter list. |
|
void Mutex::TryRemove(PerThreadSynch *s) { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
// acquire spinlock & lock |
|
if ((v & (kMuWait | kMuSpin | kMuWriter | kMuReader)) == kMuWait && |
|
mu_.compare_exchange_strong(v, v | kMuSpin | kMuWriter, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
PerThreadSynch *h = GetPerThreadSynch(v); |
|
if (h != nullptr) { |
|
PerThreadSynch *pw = h; // pw is w's predecessor |
|
PerThreadSynch *w; |
|
if ((w = pw->next) != s) { // search for thread, |
|
do { // processing at least one element |
|
// If the current element isn't equivalent to the waiter to be |
|
// removed, we can skip the entire chain. |
|
if (!MuEquivalentWaiter(s, w)) { |
|
pw = Skip(w); // so skip all that won't match |
|
// we don't have to worry about dangling skip fields |
|
// in the threads we skipped; none can point to s |
|
// because they are in a different equivalence class. |
|
} else { // seeking same condition |
|
FixSkip(w, s); // fix up any skip pointer from w to s |
|
pw = w; |
|
} |
|
// don't search further if we found the thread, or we're about to |
|
// process the first thread again. |
|
} while ((w = pw->next) != s && pw != h); |
|
} |
|
if (w == s) { // found thread; remove it |
|
// pw->skip may be non-zero here; the loop above ensured that |
|
// no ancestor of s can skip to s, so removal is safe anyway. |
|
h = Dequeue(h, pw); |
|
s->next = nullptr; |
|
s->state.store(PerThreadSynch::kAvailable, std::memory_order_release); |
|
} |
|
} |
|
intptr_t nv; |
|
do { // release spinlock and lock |
|
v = mu_.load(std::memory_order_relaxed); |
|
nv = v & (kMuDesig | kMuEvent); |
|
if (h != nullptr) { |
|
nv |= kMuWait | reinterpret_cast<intptr_t>(h); |
|
h->readers = 0; // we hold writer lock |
|
h->maybe_unlocking = false; // finished unlocking |
|
} |
|
} while (!mu_.compare_exchange_weak(v, nv, |
|
std::memory_order_release, |
|
std::memory_order_relaxed)); |
|
} |
|
} |
|
|
|
// Wait until thread "s", which must be the current thread, is removed from the |
|
// this mutex's waiter queue. If "s->waitp->timeout" has a timeout, wake up |
|
// if the wait extends past the absolute time specified, even if "s" is still |
|
// on the mutex queue. In this case, remove "s" from the queue and return |
|
// true, otherwise return false. |
|
ABSL_XRAY_LOG_ARGS(1) void Mutex::Block(PerThreadSynch *s) { |
|
while (s->state.load(std::memory_order_acquire) == PerThreadSynch::kQueued) { |
|
if (!DecrementSynchSem(this, s, s->waitp->timeout)) { |
|
// After a timeout, we go into a spin loop until we remove ourselves |
|
// from the queue, or someone else removes us. We can't be sure to be |
|
// able to remove ourselves in a single lock acquisition because this |
|
// mutex may be held, and the holder has the right to read the centre |
|
// of the waiter queue without holding the spinlock. |
|
this->TryRemove(s); |
|
int c = 0; |
|
while (s->next != nullptr) { |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
this->TryRemove(s); |
|
} |
|
if (kDebugMode) { |
|
// This ensures that we test the case that TryRemove() is called when s |
|
// is not on the queue. |
|
this->TryRemove(s); |
|
} |
|
s->waitp->timeout = KernelTimeout::Never(); // timeout is satisfied |
|
s->waitp->cond = nullptr; // condition no longer relevant for wakeups |
|
} |
|
} |
|
ABSL_RAW_CHECK(s->waitp != nullptr || s->suppress_fatal_errors, |
|
"detected illegal recursion in Mutex code"); |
|
s->waitp = nullptr; |
|
} |
|
|
|
// Wake thread w, and return the next thread in the list. |
|
PerThreadSynch *Mutex::Wakeup(PerThreadSynch *w) { |
|
PerThreadSynch *next = w->next; |
|
w->next = nullptr; |
|
w->state.store(PerThreadSynch::kAvailable, std::memory_order_release); |
|
IncrementSynchSem(this, w); |
|
|
|
return next; |
|
} |
|
|
|
static GraphId GetGraphIdLocked(Mutex *mu) |
|
ABSL_EXCLUSIVE_LOCKS_REQUIRED(deadlock_graph_mu) { |
|
if (!deadlock_graph) { // (re)create the deadlock graph. |
|
deadlock_graph = |
|
new (base_internal::LowLevelAlloc::Alloc(sizeof(*deadlock_graph))) |
|
GraphCycles; |
|
} |
|
return deadlock_graph->GetId(mu); |
|
} |
|
|
|
static GraphId GetGraphId(Mutex *mu) ABSL_LOCKS_EXCLUDED(deadlock_graph_mu) { |
|
deadlock_graph_mu.Lock(); |
|
GraphId id = GetGraphIdLocked(mu); |
|
deadlock_graph_mu.Unlock(); |
|
return id; |
|
} |
|
|
|
// Record a lock acquisition. This is used in debug mode for deadlock |
|
// detection. The held_locks pointer points to the relevant data |
|
// structure for each case. |
|
static void LockEnter(Mutex* mu, GraphId id, SynchLocksHeld *held_locks) { |
|
int n = held_locks->n; |
|
int i = 0; |
|
while (i != n && held_locks->locks[i].id != id) { |
|
i++; |
|
} |
|
if (i == n) { |
|
if (n == ABSL_ARRAYSIZE(held_locks->locks)) { |
|
held_locks->overflow = true; // lost some data |
|
} else { // we have room for lock |
|
held_locks->locks[i].mu = mu; |
|
held_locks->locks[i].count = 1; |
|
held_locks->locks[i].id = id; |
|
held_locks->n = n + 1; |
|
} |
|
} else { |
|
held_locks->locks[i].count++; |
|
} |
|
} |
|
|
|
// Record a lock release. Each call to LockEnter(mu, id, x) should be |
|
// eventually followed by a call to LockLeave(mu, id, x) by the same thread. |
|
// It does not process the event if is not needed when deadlock detection is |
|
// disabled. |
|
static void LockLeave(Mutex* mu, GraphId id, SynchLocksHeld *held_locks) { |
|
int n = held_locks->n; |
|
int i = 0; |
|
while (i != n && held_locks->locks[i].id != id) { |
|
i++; |
|
} |
|
if (i == n) { |
|
if (!held_locks->overflow) { |
|
// The deadlock id may have been reassigned after ForgetDeadlockInfo, |
|
// but in that case mu should still be present. |
|
i = 0; |
|
while (i != n && held_locks->locks[i].mu != mu) { |
|
i++; |
|
} |
|
if (i == n) { // mu missing means releasing unheld lock |
|
SynchEvent *mu_events = GetSynchEvent(mu); |
|
ABSL_RAW_LOG(FATAL, |
|
"thread releasing lock it does not hold: %p %s; " |
|
, |
|
static_cast<void *>(mu), |
|
mu_events == nullptr ? "" : mu_events->name); |
|
} |
|
} |
|
} else if (held_locks->locks[i].count == 1) { |
|
held_locks->n = n - 1; |
|
held_locks->locks[i] = held_locks->locks[n - 1]; |
|
held_locks->locks[n - 1].id = InvalidGraphId(); |
|
held_locks->locks[n - 1].mu = |
|
nullptr; // clear mu to please the leak detector. |
|
} else { |
|
assert(held_locks->locks[i].count > 0); |
|
held_locks->locks[i].count--; |
|
} |
|
} |
|
|
|
// Call LockEnter() if in debug mode and deadlock detection is enabled. |
|
static inline void DebugOnlyLockEnter(Mutex *mu) { |
|
if (kDebugMode) { |
|
if (synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
LockEnter(mu, GetGraphId(mu), Synch_GetAllLocks()); |
|
} |
|
} |
|
} |
|
|
|
// Call LockEnter() if in debug mode and deadlock detection is enabled. |
|
static inline void DebugOnlyLockEnter(Mutex *mu, GraphId id) { |
|
if (kDebugMode) { |
|
if (synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
LockEnter(mu, id, Synch_GetAllLocks()); |
|
} |
|
} |
|
} |
|
|
|
// Call LockLeave() if in debug mode and deadlock detection is enabled. |
|
static inline void DebugOnlyLockLeave(Mutex *mu) { |
|
if (kDebugMode) { |
|
if (synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
LockLeave(mu, GetGraphId(mu), Synch_GetAllLocks()); |
|
} |
|
} |
|
} |
|
|
|
static char *StackString(void **pcs, int n, char *buf, int maxlen, |
|
bool symbolize) { |
|
static const int kSymLen = 200; |
|
char sym[kSymLen]; |
|
int len = 0; |
|
for (int i = 0; i != n; i++) { |
|
if (symbolize) { |
|
if (!symbolizer(pcs[i], sym, kSymLen)) { |
|
sym[0] = '\0'; |
|
} |
|
snprintf(buf + len, maxlen - len, "%s\t@ %p %s\n", |
|
(i == 0 ? "\n" : ""), |
|
pcs[i], sym); |
|
} else { |
|
snprintf(buf + len, maxlen - len, " %p", pcs[i]); |
|
} |
|
len += strlen(&buf[len]); |
|
} |
|
return buf; |
|
} |
|
|
|
static char *CurrentStackString(char *buf, int maxlen, bool symbolize) { |
|
void *pcs[40]; |
|
return StackString(pcs, absl::GetStackTrace(pcs, ABSL_ARRAYSIZE(pcs), 2), buf, |
|
maxlen, symbolize); |
|
} |
|
|
|
namespace { |
|
enum { kMaxDeadlockPathLen = 10 }; // maximum length of a deadlock cycle; |
|
// a path this long would be remarkable |
|
// Buffers required to report a deadlock. |
|
// We do not allocate them on stack to avoid large stack frame. |
|
struct DeadlockReportBuffers { |
|
char buf[6100]; |
|
GraphId path[kMaxDeadlockPathLen]; |
|
}; |
|
|
|
struct ScopedDeadlockReportBuffers { |
|
ScopedDeadlockReportBuffers() { |
|
b = reinterpret_cast<DeadlockReportBuffers *>( |
|
base_internal::LowLevelAlloc::Alloc(sizeof(*b))); |
|
} |
|
~ScopedDeadlockReportBuffers() { base_internal::LowLevelAlloc::Free(b); } |
|
DeadlockReportBuffers *b; |
|
}; |
|
|
|
// Helper to pass to GraphCycles::UpdateStackTrace. |
|
int GetStack(void** stack, int max_depth) { |
|
return absl::GetStackTrace(stack, max_depth, 3); |
|
} |
|
} // anonymous namespace |
|
|
|
// Called in debug mode when a thread is about to acquire a lock in a way that |
|
// may block. |
|
static GraphId DeadlockCheck(Mutex *mu) { |
|
if (synch_deadlock_detection.load(std::memory_order_acquire) == |
|
OnDeadlockCycle::kIgnore) { |
|
return InvalidGraphId(); |
|
} |
|
|
|
SynchLocksHeld *all_locks = Synch_GetAllLocks(); |
|
|
|
absl::base_internal::SpinLockHolder lock(&deadlock_graph_mu); |
|
const GraphId mu_id = GetGraphIdLocked(mu); |
|
|
|
if (all_locks->n == 0) { |
|
// There are no other locks held. Return now so that we don't need to |
|
// call GetSynchEvent(). This way we do not record the stack trace |
|
// for this Mutex. It's ok, since if this Mutex is involved in a deadlock, |
|
// it can't always be the first lock acquired by a thread. |
|
return mu_id; |
|
} |
|
|
|
// We prefer to keep stack traces that show a thread holding and acquiring |
|
// as many locks as possible. This increases the chances that a given edge |
|
// in the acquires-before graph will be represented in the stack traces |
|
// recorded for the locks. |
|
deadlock_graph->UpdateStackTrace(mu_id, all_locks->n + 1, GetStack); |
|
|
|
// For each other mutex already held by this thread: |
|
for (int i = 0; i != all_locks->n; i++) { |
|
const GraphId other_node_id = all_locks->locks[i].id; |
|
const Mutex *other = |
|
static_cast<const Mutex *>(deadlock_graph->Ptr(other_node_id)); |
|
if (other == nullptr) { |
|
// Ignore stale lock |
|
continue; |
|
} |
|
|
|
// Add the acquired-before edge to the graph. |
|
if (!deadlock_graph->InsertEdge(other_node_id, mu_id)) { |
|
ScopedDeadlockReportBuffers scoped_buffers; |
|
DeadlockReportBuffers *b = scoped_buffers.b; |
|
static int number_of_reported_deadlocks = 0; |
|
number_of_reported_deadlocks++; |
|
// Symbolize only 2 first deadlock report to avoid huge slowdowns. |
|
bool symbolize = number_of_reported_deadlocks <= 2; |
|
ABSL_RAW_LOG(ERROR, "Potential Mutex deadlock: %s", |
|
CurrentStackString(b->buf, sizeof (b->buf), symbolize)); |
|
int len = 0; |
|
for (int j = 0; j != all_locks->n; j++) { |
|
void* pr = deadlock_graph->Ptr(all_locks->locks[j].id); |
|
if (pr != nullptr) { |
|
snprintf(b->buf + len, sizeof (b->buf) - len, " %p", pr); |
|
len += static_cast<int>(strlen(&b->buf[len])); |
|
} |
|
} |
|
ABSL_RAW_LOG(ERROR, |
|
"Acquiring absl::Mutex %p while holding %s; a cycle in the " |
|
"historical lock ordering graph has been observed", |
|
static_cast<void *>(mu), b->buf); |
|
ABSL_RAW_LOG(ERROR, "Cycle: "); |
|
int path_len = deadlock_graph->FindPath( |
|
mu_id, other_node_id, ABSL_ARRAYSIZE(b->path), b->path); |
|
for (int j = 0; j != path_len; j++) { |
|
GraphId id = b->path[j]; |
|
Mutex *path_mu = static_cast<Mutex *>(deadlock_graph->Ptr(id)); |
|
if (path_mu == nullptr) continue; |
|
void** stack; |
|
int depth = deadlock_graph->GetStackTrace(id, &stack); |
|
snprintf(b->buf, sizeof(b->buf), |
|
"mutex@%p stack: ", static_cast<void *>(path_mu)); |
|
StackString(stack, depth, b->buf + strlen(b->buf), |
|
static_cast<int>(sizeof(b->buf) - strlen(b->buf)), |
|
symbolize); |
|
ABSL_RAW_LOG(ERROR, "%s", b->buf); |
|
} |
|
if (synch_deadlock_detection.load(std::memory_order_acquire) == |
|
OnDeadlockCycle::kAbort) { |
|
deadlock_graph_mu.Unlock(); // avoid deadlock in fatal sighandler |
|
ABSL_RAW_LOG(FATAL, "dying due to potential deadlock"); |
|
return mu_id; |
|
} |
|
break; // report at most one potential deadlock per acquisition |
|
} |
|
} |
|
|
|
return mu_id; |
|
} |
|
|
|
// Invoke DeadlockCheck() iff we're in debug mode and |
|
// deadlock checking has been enabled. |
|
static inline GraphId DebugOnlyDeadlockCheck(Mutex *mu) { |
|
if (kDebugMode && synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
return DeadlockCheck(mu); |
|
} else { |
|
return InvalidGraphId(); |
|
} |
|
} |
|
|
|
void Mutex::ForgetDeadlockInfo() { |
|
if (kDebugMode && synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
deadlock_graph_mu.Lock(); |
|
if (deadlock_graph != nullptr) { |
|
deadlock_graph->RemoveNode(this); |
|
} |
|
deadlock_graph_mu.Unlock(); |
|
} |
|
} |
|
|
|
void Mutex::AssertNotHeld() const { |
|
// We have the data to allow this check only if in debug mode and deadlock |
|
// detection is enabled. |
|
if (kDebugMode && |
|
(mu_.load(std::memory_order_relaxed) & (kMuWriter | kMuReader)) != 0 && |
|
synch_deadlock_detection.load(std::memory_order_acquire) != |
|
OnDeadlockCycle::kIgnore) { |
|
GraphId id = GetGraphId(const_cast<Mutex *>(this)); |
|
SynchLocksHeld *locks = Synch_GetAllLocks(); |
|
for (int i = 0; i != locks->n; i++) { |
|
if (locks->locks[i].id == id) { |
|
SynchEvent *mu_events = GetSynchEvent(this); |
|
ABSL_RAW_LOG(FATAL, "thread should not hold mutex %p %s", |
|
static_cast<const void *>(this), |
|
(mu_events == nullptr ? "" : mu_events->name)); |
|
} |
|
} |
|
} |
|
} |
|
|
|
// Attempt to acquire *mu, and return whether successful. The implementation |
|
// may spin for a short while if the lock cannot be acquired immediately. |
|
static bool TryAcquireWithSpinning(std::atomic<intptr_t>* mu) { |
|
int c = GetMutexGlobals().spinloop_iterations; |
|
do { // do/while somewhat faster on AMD |
|
intptr_t v = mu->load(std::memory_order_relaxed); |
|
if ((v & (kMuReader|kMuEvent)) != 0) { |
|
return false; // a reader or tracing -> give up |
|
} else if (((v & kMuWriter) == 0) && // no holder -> try to acquire |
|
mu->compare_exchange_strong(v, kMuWriter | v, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
return true; |
|
} |
|
} while (--c > 0); |
|
return false; |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) void Mutex::Lock() { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, 0); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
// try fast acquire, then spin loop |
|
if ((v & (kMuWriter | kMuReader | kMuEvent)) != 0 || |
|
!mu_.compare_exchange_strong(v, kMuWriter | v, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
// try spin acquire, then slow loop |
|
if (!TryAcquireWithSpinning(&this->mu_)) { |
|
this->LockSlow(kExclusive, nullptr, 0); |
|
} |
|
} |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0); |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) void Mutex::ReaderLock() { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_read_lock); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
// try fast acquire, then slow loop |
|
if ((v & (kMuWriter | kMuWait | kMuEvent)) != 0 || |
|
!mu_.compare_exchange_strong(v, (kMuReader | v) + kMuOne, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
this->LockSlow(kShared, nullptr, 0); |
|
} |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_read_lock, 0); |
|
} |
|
|
|
void Mutex::LockWhen(const Condition &cond) { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, 0); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
this->LockSlow(kExclusive, &cond, 0); |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0); |
|
} |
|
|
|
bool Mutex::LockWhenWithTimeout(const Condition &cond, absl::Duration timeout) { |
|
return LockWhenWithDeadline(cond, DeadlineFromTimeout(timeout)); |
|
} |
|
|
|
bool Mutex::LockWhenWithDeadline(const Condition &cond, absl::Time deadline) { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, 0); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
bool res = LockSlowWithDeadline(kExclusive, &cond, |
|
KernelTimeout(deadline), 0); |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0); |
|
return res; |
|
} |
|
|
|
void Mutex::ReaderLockWhen(const Condition &cond) { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_read_lock); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
this->LockSlow(kShared, &cond, 0); |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_read_lock, 0); |
|
} |
|
|
|
bool Mutex::ReaderLockWhenWithTimeout(const Condition &cond, |
|
absl::Duration timeout) { |
|
return ReaderLockWhenWithDeadline(cond, DeadlineFromTimeout(timeout)); |
|
} |
|
|
|
bool Mutex::ReaderLockWhenWithDeadline(const Condition &cond, |
|
absl::Time deadline) { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_read_lock); |
|
GraphId id = DebugOnlyDeadlockCheck(this); |
|
bool res = LockSlowWithDeadline(kShared, &cond, KernelTimeout(deadline), 0); |
|
DebugOnlyLockEnter(this, id); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_read_lock, 0); |
|
return res; |
|
} |
|
|
|
void Mutex::Await(const Condition &cond) { |
|
if (cond.Eval()) { // condition already true; nothing to do |
|
if (kDebugMode) { |
|
this->AssertReaderHeld(); |
|
} |
|
} else { // normal case |
|
ABSL_RAW_CHECK(this->AwaitCommon(cond, KernelTimeout::Never()), |
|
"condition untrue on return from Await"); |
|
} |
|
} |
|
|
|
bool Mutex::AwaitWithTimeout(const Condition &cond, absl::Duration timeout) { |
|
return AwaitWithDeadline(cond, DeadlineFromTimeout(timeout)); |
|
} |
|
|
|
bool Mutex::AwaitWithDeadline(const Condition &cond, absl::Time deadline) { |
|
if (cond.Eval()) { // condition already true; nothing to do |
|
if (kDebugMode) { |
|
this->AssertReaderHeld(); |
|
} |
|
return true; |
|
} |
|
|
|
KernelTimeout t{deadline}; |
|
bool res = this->AwaitCommon(cond, t); |
|
ABSL_RAW_CHECK(res || t.has_timeout(), |
|
"condition untrue on return from Await"); |
|
return res; |
|
} |
|
|
|
bool Mutex::AwaitCommon(const Condition &cond, KernelTimeout t) { |
|
this->AssertReaderHeld(); |
|
MuHow how = |
|
(mu_.load(std::memory_order_relaxed) & kMuWriter) ? kExclusive : kShared; |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(this, TsanFlags(how)); |
|
SynchWaitParams waitp( |
|
how, &cond, t, nullptr /*no cvmu*/, Synch_GetPerThreadAnnotated(this), |
|
nullptr /*no cv_word*/); |
|
int flags = kMuHasBlocked; |
|
if (!Condition::GuaranteedEqual(&cond, nullptr)) { |
|
flags |= kMuIsCond; |
|
} |
|
this->UnlockSlow(&waitp); |
|
this->Block(waitp.thread); |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(this, TsanFlags(how)); |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, TsanFlags(how)); |
|
this->LockSlowLoop(&waitp, flags); |
|
bool res = waitp.cond != nullptr || // => cond known true from LockSlowLoop |
|
EvalConditionAnnotated(&cond, this, true, false, how == kShared); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, TsanFlags(how), 0); |
|
return res; |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) bool Mutex::TryLock() { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_try_lock); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
if ((v & (kMuWriter | kMuReader | kMuEvent)) == 0 && // try fast acquire |
|
mu_.compare_exchange_strong(v, kMuWriter | v, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
DebugOnlyLockEnter(this); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_try_lock, 0); |
|
return true; |
|
} |
|
if ((v & kMuEvent) != 0) { // we're recording events |
|
if ((v & kExclusive->slow_need_zero) == 0 && // try fast acquire |
|
mu_.compare_exchange_strong( |
|
v, (kExclusive->fast_or | v) + kExclusive->fast_add, |
|
std::memory_order_acquire, std::memory_order_relaxed)) { |
|
DebugOnlyLockEnter(this); |
|
PostSynchEvent(this, SYNCH_EV_TRYLOCK_SUCCESS); |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, __tsan_mutex_try_lock, 0); |
|
return true; |
|
} else { |
|
PostSynchEvent(this, SYNCH_EV_TRYLOCK_FAILED); |
|
} |
|
} |
|
ABSL_TSAN_MUTEX_POST_LOCK( |
|
this, __tsan_mutex_try_lock | __tsan_mutex_try_lock_failed, 0); |
|
return false; |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) bool Mutex::ReaderTryLock() { |
|
ABSL_TSAN_MUTEX_PRE_LOCK(this, |
|
__tsan_mutex_read_lock | __tsan_mutex_try_lock); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
// The while-loops (here and below) iterate only if the mutex word keeps |
|
// changing (typically because the reader count changes) under the CAS. We |
|
// limit the number of attempts to avoid having to think about livelock. |
|
int loop_limit = 5; |
|
while ((v & (kMuWriter|kMuWait|kMuEvent)) == 0 && loop_limit != 0) { |
|
if (mu_.compare_exchange_strong(v, (kMuReader | v) + kMuOne, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
DebugOnlyLockEnter(this); |
|
ABSL_TSAN_MUTEX_POST_LOCK( |
|
this, __tsan_mutex_read_lock | __tsan_mutex_try_lock, 0); |
|
return true; |
|
} |
|
loop_limit--; |
|
v = mu_.load(std::memory_order_relaxed); |
|
} |
|
if ((v & kMuEvent) != 0) { // we're recording events |
|
loop_limit = 5; |
|
while ((v & kShared->slow_need_zero) == 0 && loop_limit != 0) { |
|
if (mu_.compare_exchange_strong(v, (kMuReader | v) + kMuOne, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
DebugOnlyLockEnter(this); |
|
PostSynchEvent(this, SYNCH_EV_READERTRYLOCK_SUCCESS); |
|
ABSL_TSAN_MUTEX_POST_LOCK( |
|
this, __tsan_mutex_read_lock | __tsan_mutex_try_lock, 0); |
|
return true; |
|
} |
|
loop_limit--; |
|
v = mu_.load(std::memory_order_relaxed); |
|
} |
|
if ((v & kMuEvent) != 0) { |
|
PostSynchEvent(this, SYNCH_EV_READERTRYLOCK_FAILED); |
|
} |
|
} |
|
ABSL_TSAN_MUTEX_POST_LOCK(this, |
|
__tsan_mutex_read_lock | __tsan_mutex_try_lock | |
|
__tsan_mutex_try_lock_failed, |
|
0); |
|
return false; |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) void Mutex::Unlock() { |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0); |
|
DebugOnlyLockLeave(this); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
|
|
if (kDebugMode && ((v & (kMuWriter | kMuReader)) != kMuWriter)) { |
|
ABSL_RAW_LOG(FATAL, "Mutex unlocked when destroyed or not locked: v=0x%x", |
|
static_cast<unsigned>(v)); |
|
} |
|
|
|
// should_try_cas is whether we'll try a compare-and-swap immediately. |
|
// NOTE: optimized out when kDebugMode is false. |
|
bool should_try_cas = ((v & (kMuEvent | kMuWriter)) == kMuWriter && |
|
(v & (kMuWait | kMuDesig)) != kMuWait); |
|
// But, we can use an alternate computation of it, that compilers |
|
// currently don't find on their own. When that changes, this function |
|
// can be simplified. |
|
intptr_t x = (v ^ (kMuWriter | kMuWait)) & (kMuWriter | kMuEvent); |
|
intptr_t y = (v ^ (kMuWriter | kMuWait)) & (kMuWait | kMuDesig); |
|
// Claim: "x == 0 && y > 0" is equal to should_try_cas. |
|
// Also, because kMuWriter and kMuEvent exceed kMuDesig and kMuWait, |
|
// all possible non-zero values for x exceed all possible values for y. |
|
// Therefore, (x == 0 && y > 0) == (x < y). |
|
if (kDebugMode && should_try_cas != (x < y)) { |
|
// We would usually use PRIdPTR here, but is not correctly implemented |
|
// within the android toolchain. |
|
ABSL_RAW_LOG(FATAL, "internal logic error %llx %llx %llx\n", |
|
static_cast<long long>(v), static_cast<long long>(x), |
|
static_cast<long long>(y)); |
|
} |
|
if (x < y && |
|
mu_.compare_exchange_strong(v, v & ~(kMuWrWait | kMuWriter), |
|
std::memory_order_release, |
|
std::memory_order_relaxed)) { |
|
// fast writer release (writer with no waiters or with designated waker) |
|
} else { |
|
this->UnlockSlow(nullptr /*no waitp*/); // take slow path |
|
} |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(this, 0); |
|
} |
|
|
|
// Requires v to represent a reader-locked state. |
|
static bool ExactlyOneReader(intptr_t v) { |
|
assert((v & (kMuWriter|kMuReader)) == kMuReader); |
|
assert((v & kMuHigh) != 0); |
|
// The more straightforward "(v & kMuHigh) == kMuOne" also works, but |
|
// on some architectures the following generates slightly smaller code. |
|
// It may be faster too. |
|
constexpr intptr_t kMuMultipleWaitersMask = kMuHigh ^ kMuOne; |
|
return (v & kMuMultipleWaitersMask) == 0; |
|
} |
|
|
|
ABSL_XRAY_LOG_ARGS(1) void Mutex::ReaderUnlock() { |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(this, __tsan_mutex_read_lock); |
|
DebugOnlyLockLeave(this); |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
assert((v & (kMuWriter|kMuReader)) == kMuReader); |
|
if ((v & (kMuReader|kMuWait|kMuEvent)) == kMuReader) { |
|
// fast reader release (reader with no waiters) |
|
intptr_t clear = ExactlyOneReader(v) ? kMuReader|kMuOne : kMuOne; |
|
if (mu_.compare_exchange_strong(v, v - clear, |
|
std::memory_order_release, |
|
std::memory_order_relaxed)) { |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(this, __tsan_mutex_read_lock); |
|
return; |
|
} |
|
} |
|
this->UnlockSlow(nullptr /*no waitp*/); // take slow path |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(this, __tsan_mutex_read_lock); |
|
} |
|
|
|
// The zap_desig_waker bitmask is used to clear the designated waker flag in |
|
// the mutex if this thread has blocked, and therefore may be the designated |
|
// waker. |
|
static const intptr_t zap_desig_waker[] = { |
|
~static_cast<intptr_t>(0), // not blocked |
|
~static_cast<intptr_t>( |
|
kMuDesig) // blocked; turn off the designated waker bit |
|
}; |
|
|
|
// The ignore_waiting_writers bitmask is used to ignore the existence |
|
// of waiting writers if a reader that has already blocked once |
|
// wakes up. |
|
static const intptr_t ignore_waiting_writers[] = { |
|
~static_cast<intptr_t>(0), // not blocked |
|
~static_cast<intptr_t>( |
|
kMuWrWait) // blocked; pretend there are no waiting writers |
|
}; |
|
|
|
// Internal version of LockWhen(). See LockSlowWithDeadline() |
|
ABSL_ATTRIBUTE_NOINLINE void Mutex::LockSlow(MuHow how, const Condition *cond, |
|
int flags) { |
|
ABSL_RAW_CHECK( |
|
this->LockSlowWithDeadline(how, cond, KernelTimeout::Never(), flags), |
|
"condition untrue on return from LockSlow"); |
|
} |
|
|
|
// Compute cond->Eval() and tell race detectors that we do it under mutex mu. |
|
static inline bool EvalConditionAnnotated(const Condition *cond, Mutex *mu, |
|
bool locking, bool trylock, |
|
bool read_lock) { |
|
// Delicate annotation dance. |
|
// We are currently inside of read/write lock/unlock operation. |
|
// All memory accesses are ignored inside of mutex operations + for unlock |
|
// operation tsan considers that we've already released the mutex. |
|
bool res = false; |
|
#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE |
|
const int flags = read_lock ? __tsan_mutex_read_lock : 0; |
|
const int tryflags = flags | (trylock ? __tsan_mutex_try_lock : 0); |
|
#endif |
|
if (locking) { |
|
// For lock we pretend that we have finished the operation, |
|
// evaluate the predicate, then unlock the mutex and start locking it again |
|
// to match the annotation at the end of outer lock operation. |
|
// Note: we can't simply do POST_LOCK, Eval, PRE_LOCK, because then tsan |
|
// will think the lock acquisition is recursive which will trigger |
|
// deadlock detector. |
|
ABSL_TSAN_MUTEX_POST_LOCK(mu, tryflags, 0); |
|
res = cond->Eval(); |
|
// There is no "try" version of Unlock, so use flags instead of tryflags. |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(mu, flags); |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(mu, flags); |
|
ABSL_TSAN_MUTEX_PRE_LOCK(mu, tryflags); |
|
} else { |
|
// Similarly, for unlock we pretend that we have unlocked the mutex, |
|
// lock the mutex, evaluate the predicate, and start unlocking it again |
|
// to match the annotation at the end of outer unlock operation. |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(mu, flags); |
|
ABSL_TSAN_MUTEX_PRE_LOCK(mu, flags); |
|
ABSL_TSAN_MUTEX_POST_LOCK(mu, flags, 0); |
|
res = cond->Eval(); |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(mu, flags); |
|
} |
|
// Prevent unused param warnings in non-TSAN builds. |
|
static_cast<void>(mu); |
|
static_cast<void>(trylock); |
|
static_cast<void>(read_lock); |
|
return res; |
|
} |
|
|
|
// Compute cond->Eval() hiding it from race detectors. |
|
// We are hiding it because inside of UnlockSlow we can evaluate a predicate |
|
// that was just added by a concurrent Lock operation; Lock adds the predicate |
|
// to the internal Mutex list without actually acquiring the Mutex |
|
// (it only acquires the internal spinlock, which is rightfully invisible for |
|
// tsan). As the result there is no tsan-visible synchronization between the |
|
// addition and this thread. So if we would enable race detection here, |
|
// it would race with the predicate initialization. |
|
static inline bool EvalConditionIgnored(Mutex *mu, const Condition *cond) { |
|
// Memory accesses are already ignored inside of lock/unlock operations, |
|
// but synchronization operations are also ignored. When we evaluate the |
|
// predicate we must ignore only memory accesses but not synchronization, |
|
// because missed synchronization can lead to false reports later. |
|
// So we "divert" (which un-ignores both memory accesses and synchronization) |
|
// and then separately turn on ignores of memory accesses. |
|
ABSL_TSAN_MUTEX_PRE_DIVERT(mu, 0); |
|
ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN(); |
|
bool res = cond->Eval(); |
|
ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END(); |
|
ABSL_TSAN_MUTEX_POST_DIVERT(mu, 0); |
|
static_cast<void>(mu); // Prevent unused param warning in non-TSAN builds. |
|
return res; |
|
} |
|
|
|
// Internal equivalent of *LockWhenWithDeadline(), where |
|
// "t" represents the absolute timeout; !t.has_timeout() means "forever". |
|
// "how" is "kShared" (for ReaderLockWhen) or "kExclusive" (for LockWhen) |
|
// In flags, bits are ored together: |
|
// - kMuHasBlocked indicates that the client has already blocked on the call so |
|
// the designated waker bit must be cleared and waiting writers should not |
|
// obstruct this call |
|
// - kMuIsCond indicates that this is a conditional acquire (condition variable, |
|
// Await, LockWhen) so contention profiling should be suppressed. |
|
bool Mutex::LockSlowWithDeadline(MuHow how, const Condition *cond, |
|
KernelTimeout t, int flags) { |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
bool unlock = false; |
|
if ((v & how->fast_need_zero) == 0 && // try fast acquire |
|
mu_.compare_exchange_strong( |
|
v, (how->fast_or | (v & zap_desig_waker[flags & kMuHasBlocked])) + |
|
how->fast_add, |
|
std::memory_order_acquire, std::memory_order_relaxed)) { |
|
if (cond == nullptr || |
|
EvalConditionAnnotated(cond, this, true, false, how == kShared)) { |
|
return true; |
|
} |
|
unlock = true; |
|
} |
|
SynchWaitParams waitp( |
|
how, cond, t, nullptr /*no cvmu*/, Synch_GetPerThreadAnnotated(this), |
|
nullptr /*no cv_word*/); |
|
if (!Condition::GuaranteedEqual(cond, nullptr)) { |
|
flags |= kMuIsCond; |
|
} |
|
if (unlock) { |
|
this->UnlockSlow(&waitp); |
|
this->Block(waitp.thread); |
|
flags |= kMuHasBlocked; |
|
} |
|
this->LockSlowLoop(&waitp, flags); |
|
return waitp.cond != nullptr || // => cond known true from LockSlowLoop |
|
cond == nullptr || |
|
EvalConditionAnnotated(cond, this, true, false, how == kShared); |
|
} |
|
|
|
// RAW_CHECK_FMT() takes a condition, a printf-style format string, and |
|
// the printf-style argument list. The format string must be a literal. |
|
// Arguments after the first are not evaluated unless the condition is true. |
|
#define RAW_CHECK_FMT(cond, ...) \ |
|
do { \ |
|
if (ABSL_PREDICT_FALSE(!(cond))) { \ |
|
ABSL_RAW_LOG(FATAL, "Check " #cond " failed: " __VA_ARGS__); \ |
|
} \ |
|
} while (0) |
|
|
|
static void CheckForMutexCorruption(intptr_t v, const char* label) { |
|
// Test for either of two situations that should not occur in v: |
|
// kMuWriter and kMuReader |
|
// kMuWrWait and !kMuWait |
|
const uintptr_t w = v ^ kMuWait; |
|
// By flipping that bit, we can now test for: |
|
// kMuWriter and kMuReader in w |
|
// kMuWrWait and kMuWait in w |
|
// We've chosen these two pairs of values to be so that they will overlap, |
|
// respectively, when the word is left shifted by three. This allows us to |
|
// save a branch in the common (correct) case of them not being coincident. |
|
static_assert(kMuReader << 3 == kMuWriter, "must match"); |
|
static_assert(kMuWait << 3 == kMuWrWait, "must match"); |
|
if (ABSL_PREDICT_TRUE((w & (w << 3) & (kMuWriter | kMuWrWait)) == 0)) return; |
|
RAW_CHECK_FMT((v & (kMuWriter | kMuReader)) != (kMuWriter | kMuReader), |
|
"%s: Mutex corrupt: both reader and writer lock held: %p", |
|
label, reinterpret_cast<void *>(v)); |
|
RAW_CHECK_FMT((v & (kMuWait | kMuWrWait)) != kMuWrWait, |
|
"%s: Mutex corrupt: waiting writer with no waiters: %p", |
|
label, reinterpret_cast<void *>(v)); |
|
assert(false); |
|
} |
|
|
|
void Mutex::LockSlowLoop(SynchWaitParams *waitp, int flags) { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
int c = 0; |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
if ((v & kMuEvent) != 0) { |
|
PostSynchEvent(this, |
|
waitp->how == kExclusive? SYNCH_EV_LOCK: SYNCH_EV_READERLOCK); |
|
} |
|
ABSL_RAW_CHECK( |
|
waitp->thread->waitp == nullptr || waitp->thread->suppress_fatal_errors, |
|
"detected illegal recursion into Mutex code"); |
|
for (;;) { |
|
v = mu_.load(std::memory_order_relaxed); |
|
CheckForMutexCorruption(v, "Lock"); |
|
if ((v & waitp->how->slow_need_zero) == 0) { |
|
if (mu_.compare_exchange_strong( |
|
v, (waitp->how->fast_or | |
|
(v & zap_desig_waker[flags & kMuHasBlocked])) + |
|
waitp->how->fast_add, |
|
std::memory_order_acquire, std::memory_order_relaxed)) { |
|
if (waitp->cond == nullptr || |
|
EvalConditionAnnotated(waitp->cond, this, true, false, |
|
waitp->how == kShared)) { |
|
break; // we timed out, or condition true, so return |
|
} |
|
this->UnlockSlow(waitp); // got lock but condition false |
|
this->Block(waitp->thread); |
|
flags |= kMuHasBlocked; |
|
c = 0; |
|
} |
|
} else { // need to access waiter list |
|
bool dowait = false; |
|
if ((v & (kMuSpin|kMuWait)) == 0) { // no waiters |
|
// This thread tries to become the one and only waiter. |
|
PerThreadSynch *new_h = Enqueue(nullptr, waitp, v, flags); |
|
intptr_t nv = (v & zap_desig_waker[flags & kMuHasBlocked] & kMuLow) | |
|
kMuWait; |
|
ABSL_RAW_CHECK(new_h != nullptr, "Enqueue to empty list failed"); |
|
if (waitp->how == kExclusive && (v & kMuReader) != 0) { |
|
nv |= kMuWrWait; |
|
} |
|
if (mu_.compare_exchange_strong( |
|
v, reinterpret_cast<intptr_t>(new_h) | nv, |
|
std::memory_order_release, std::memory_order_relaxed)) { |
|
dowait = true; |
|
} else { // attempted Enqueue() failed |
|
// zero out the waitp field set by Enqueue() |
|
waitp->thread->waitp = nullptr; |
|
} |
|
} else if ((v & waitp->how->slow_inc_need_zero & |
|
ignore_waiting_writers[flags & kMuHasBlocked]) == 0) { |
|
// This is a reader that needs to increment the reader count, |
|
// but the count is currently held in the last waiter. |
|
if (mu_.compare_exchange_strong( |
|
v, (v & zap_desig_waker[flags & kMuHasBlocked]) | kMuSpin | |
|
kMuReader, |
|
std::memory_order_acquire, std::memory_order_relaxed)) { |
|
PerThreadSynch *h = GetPerThreadSynch(v); |
|
h->readers += kMuOne; // inc reader count in waiter |
|
do { // release spinlock |
|
v = mu_.load(std::memory_order_relaxed); |
|
} while (!mu_.compare_exchange_weak(v, (v & ~kMuSpin) | kMuReader, |
|
std::memory_order_release, |
|
std::memory_order_relaxed)); |
|
if (waitp->cond == nullptr || |
|
EvalConditionAnnotated(waitp->cond, this, true, false, |
|
waitp->how == kShared)) { |
|
break; // we timed out, or condition true, so return |
|
} |
|
this->UnlockSlow(waitp); // got lock but condition false |
|
this->Block(waitp->thread); |
|
flags |= kMuHasBlocked; |
|
c = 0; |
|
} |
|
} else if ((v & kMuSpin) == 0 && // attempt to queue ourselves |
|
mu_.compare_exchange_strong( |
|
v, (v & zap_desig_waker[flags & kMuHasBlocked]) | kMuSpin | |
|
kMuWait, |
|
std::memory_order_acquire, std::memory_order_relaxed)) { |
|
PerThreadSynch *h = GetPerThreadSynch(v); |
|
PerThreadSynch *new_h = Enqueue(h, waitp, v, flags); |
|
intptr_t wr_wait = 0; |
|
ABSL_RAW_CHECK(new_h != nullptr, "Enqueue to list failed"); |
|
if (waitp->how == kExclusive && (v & kMuReader) != 0) { |
|
wr_wait = kMuWrWait; // give priority to a waiting writer |
|
} |
|
do { // release spinlock |
|
v = mu_.load(std::memory_order_relaxed); |
|
} while (!mu_.compare_exchange_weak( |
|
v, (v & (kMuLow & ~kMuSpin)) | kMuWait | wr_wait | |
|
reinterpret_cast<intptr_t>(new_h), |
|
std::memory_order_release, std::memory_order_relaxed)); |
|
dowait = true; |
|
} |
|
if (dowait) { |
|
this->Block(waitp->thread); // wait until removed from list or timeout |
|
flags |= kMuHasBlocked; |
|
c = 0; |
|
} |
|
} |
|
ABSL_RAW_CHECK( |
|
waitp->thread->waitp == nullptr || waitp->thread->suppress_fatal_errors, |
|
"detected illegal recursion into Mutex code"); |
|
// delay, then try again |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
} |
|
ABSL_RAW_CHECK( |
|
waitp->thread->waitp == nullptr || waitp->thread->suppress_fatal_errors, |
|
"detected illegal recursion into Mutex code"); |
|
if ((v & kMuEvent) != 0) { |
|
PostSynchEvent(this, |
|
waitp->how == kExclusive? SYNCH_EV_LOCK_RETURNING : |
|
SYNCH_EV_READERLOCK_RETURNING); |
|
} |
|
} |
|
|
|
// Unlock this mutex, which is held by the current thread. |
|
// If waitp is non-zero, it must be the wait parameters for the current thread |
|
// which holds the lock but is not runnable because its condition is false |
|
// or it is in the process of blocking on a condition variable; it must requeue |
|
// itself on the mutex/condvar to wait for its condition to become true. |
|
ABSL_ATTRIBUTE_NOINLINE void Mutex::UnlockSlow(SynchWaitParams *waitp) { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
this->AssertReaderHeld(); |
|
CheckForMutexCorruption(v, "Unlock"); |
|
if ((v & kMuEvent) != 0) { |
|
PostSynchEvent(this, |
|
(v & kMuWriter) != 0? SYNCH_EV_UNLOCK: SYNCH_EV_READERUNLOCK); |
|
} |
|
int c = 0; |
|
// the waiter under consideration to wake, or zero |
|
PerThreadSynch *w = nullptr; |
|
// the predecessor to w or zero |
|
PerThreadSynch *pw = nullptr; |
|
// head of the list searched previously, or zero |
|
PerThreadSynch *old_h = nullptr; |
|
// a condition that's known to be false. |
|
const Condition *known_false = nullptr; |
|
PerThreadSynch *wake_list = kPerThreadSynchNull; // list of threads to wake |
|
intptr_t wr_wait = 0; // set to kMuWrWait if we wake a reader and a |
|
// later writer could have acquired the lock |
|
// (starvation avoidance) |
|
ABSL_RAW_CHECK(waitp == nullptr || waitp->thread->waitp == nullptr || |
|
waitp->thread->suppress_fatal_errors, |
|
"detected illegal recursion into Mutex code"); |
|
// This loop finds threads wake_list to wakeup if any, and removes them from |
|
// the list of waiters. In addition, it places waitp.thread on the queue of |
|
// waiters if waitp is non-zero. |
|
for (;;) { |
|
v = mu_.load(std::memory_order_relaxed); |
|
if ((v & kMuWriter) != 0 && (v & (kMuWait | kMuDesig)) != kMuWait && |
|
waitp == nullptr) { |
|
// fast writer release (writer with no waiters or with designated waker) |
|
if (mu_.compare_exchange_strong(v, v & ~(kMuWrWait | kMuWriter), |
|
std::memory_order_release, |
|
std::memory_order_relaxed)) { |
|
return; |
|
} |
|
} else if ((v & (kMuReader | kMuWait)) == kMuReader && waitp == nullptr) { |
|
// fast reader release (reader with no waiters) |
|
intptr_t clear = ExactlyOneReader(v) ? kMuReader | kMuOne : kMuOne; |
|
if (mu_.compare_exchange_strong(v, v - clear, |
|
std::memory_order_release, |
|
std::memory_order_relaxed)) { |
|
return; |
|
} |
|
} else if ((v & kMuSpin) == 0 && // attempt to get spinlock |
|
mu_.compare_exchange_strong(v, v | kMuSpin, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
if ((v & kMuWait) == 0) { // no one to wake |
|
intptr_t nv; |
|
bool do_enqueue = true; // always Enqueue() the first time |
|
ABSL_RAW_CHECK(waitp != nullptr, |
|
"UnlockSlow is confused"); // about to sleep |
|
do { // must loop to release spinlock as reader count may change |
|
v = mu_.load(std::memory_order_relaxed); |
|
// decrement reader count if there are readers |
|
intptr_t new_readers = (v >= kMuOne)? v - kMuOne : v; |
|
PerThreadSynch *new_h = nullptr; |
|
if (do_enqueue) { |
|
// If we are enqueuing on a CondVar (waitp->cv_word != nullptr) then |
|
// we must not retry here. The initial attempt will always have |
|
// succeeded, further attempts would enqueue us against *this due to |
|
// Fer() handling. |
|
do_enqueue = (waitp->cv_word == nullptr); |
|
new_h = Enqueue(nullptr, waitp, new_readers, kMuIsCond); |
|
} |
|
intptr_t clear = kMuWrWait | kMuWriter; // by default clear write bit |
|
if ((v & kMuWriter) == 0 && ExactlyOneReader(v)) { // last reader |
|
clear = kMuWrWait | kMuReader; // clear read bit |
|
} |
|
nv = (v & kMuLow & ~clear & ~kMuSpin); |
|
if (new_h != nullptr) { |
|
nv |= kMuWait | reinterpret_cast<intptr_t>(new_h); |
|
} else { // new_h could be nullptr if we queued ourselves on a |
|
// CondVar |
|
// In that case, we must place the reader count back in the mutex |
|
// word, as Enqueue() did not store it in the new waiter. |
|
nv |= new_readers & kMuHigh; |
|
} |
|
// release spinlock & our lock; retry if reader-count changed |
|
// (writer count cannot change since we hold lock) |
|
} while (!mu_.compare_exchange_weak(v, nv, |
|
std::memory_order_release, |
|
std::memory_order_relaxed)); |
|
break; |
|
} |
|
|
|
// There are waiters. |
|
// Set h to the head of the circular waiter list. |
|
PerThreadSynch *h = GetPerThreadSynch(v); |
|
if ((v & kMuReader) != 0 && (h->readers & kMuHigh) > kMuOne) { |
|
// a reader but not the last |
|
h->readers -= kMuOne; // release our lock |
|
intptr_t nv = v; // normally just release spinlock |
|
if (waitp != nullptr) { // but waitp!=nullptr => must queue ourselves |
|
PerThreadSynch *new_h = Enqueue(h, waitp, v, kMuIsCond); |
|
ABSL_RAW_CHECK(new_h != nullptr, |
|
"waiters disappeared during Enqueue()!"); |
|
nv &= kMuLow; |
|
nv |= kMuWait | reinterpret_cast<intptr_t>(new_h); |
|
} |
|
mu_.store(nv, std::memory_order_release); // release spinlock |
|
// can release with a store because there were waiters |
|
break; |
|
} |
|
|
|
// Either we didn't search before, or we marked the queue |
|
// as "maybe_unlocking" and no one else should have changed it. |
|
ABSL_RAW_CHECK(old_h == nullptr || h->maybe_unlocking, |
|
"Mutex queue changed beneath us"); |
|
|
|
// The lock is becoming free, and there's a waiter |
|
if (old_h != nullptr && |
|
!old_h->may_skip) { // we used old_h as a terminator |
|
old_h->may_skip = true; // allow old_h to skip once more |
|
ABSL_RAW_CHECK(old_h->skip == nullptr, "illegal skip from head"); |
|
if (h != old_h && MuEquivalentWaiter(old_h, old_h->next)) { |
|
old_h->skip = old_h->next; // old_h not head & can skip to successor |
|
} |
|
} |
|
if (h->next->waitp->how == kExclusive && |
|
Condition::GuaranteedEqual(h->next->waitp->cond, nullptr)) { |
|
// easy case: writer with no condition; no need to search |
|
pw = h; // wake w, the successor of h (=pw) |
|
w = h->next; |
|
w->wake = true; |
|
// We are waking up a writer. This writer may be racing against |
|
// an already awake reader for the lock. We want the |
|
// writer to usually win this race, |
|
// because if it doesn't, we can potentially keep taking a reader |
|
// perpetually and writers will starve. Worse than |
|
// that, this can also starve other readers if kMuWrWait gets set |
|
// later. |
|
wr_wait = kMuWrWait; |
|
} else if (w != nullptr && (w->waitp->how == kExclusive || h == old_h)) { |
|
// we found a waiter w to wake on a previous iteration and either it's |
|
// a writer, or we've searched the entire list so we have all the |
|
// readers. |
|
if (pw == nullptr) { // if w's predecessor is unknown, it must be h |
|
pw = h; |
|
} |
|
} else { |
|
// At this point we don't know all the waiters to wake, and the first |
|
// waiter has a condition or is a reader. We avoid searching over |
|
// waiters we've searched on previous iterations by starting at |
|
// old_h if it's set. If old_h==h, there's no one to wakeup at all. |
|
if (old_h == h) { // we've searched before, and nothing's new |
|
// so there's no one to wake. |
|
intptr_t nv = (v & ~(kMuReader|kMuWriter|kMuWrWait)); |
|
h->readers = 0; |
|
h->maybe_unlocking = false; // finished unlocking |
|
if (waitp != nullptr) { // we must queue ourselves and sleep |
|
PerThreadSynch *new_h = Enqueue(h, waitp, v, kMuIsCond); |
|
nv &= kMuLow; |
|
if (new_h != nullptr) { |
|
nv |= kMuWait | reinterpret_cast<intptr_t>(new_h); |
|
} // else new_h could be nullptr if we queued ourselves on a |
|
// CondVar |
|
} |
|
// release spinlock & lock |
|
// can release with a store because there were waiters |
|
mu_.store(nv, std::memory_order_release); |
|
break; |
|
} |
|
|
|
// set up to walk the list |
|
PerThreadSynch *w_walk; // current waiter during list walk |
|
PerThreadSynch *pw_walk; // previous waiter during list walk |
|
if (old_h != nullptr) { // we've searched up to old_h before |
|
pw_walk = old_h; |
|
w_walk = old_h->next; |
|
} else { // no prior search, start at beginning |
|
pw_walk = |
|
nullptr; // h->next's predecessor may change; don't record it |
|
w_walk = h->next; |
|
} |
|
|
|
h->may_skip = false; // ensure we never skip past h in future searches |
|
// even if other waiters are queued after it. |
|
ABSL_RAW_CHECK(h->skip == nullptr, "illegal skip from head"); |
|
|
|
h->maybe_unlocking = true; // we're about to scan the waiter list |
|
// without the spinlock held. |
|
// Enqueue must be conservative about |
|
// priority queuing. |
|
|
|
// We must release the spinlock to evaluate the conditions. |
|
mu_.store(v, std::memory_order_release); // release just spinlock |
|
// can release with a store because there were waiters |
|
|
|
// h is the last waiter queued, and w_walk the first unsearched waiter. |
|
// Without the spinlock, the locations mu_ and h->next may now change |
|
// underneath us, but since we hold the lock itself, the only legal |
|
// change is to add waiters between h and w_walk. Therefore, it's safe |
|
// to walk the path from w_walk to h inclusive. (TryRemove() can remove |
|
// a waiter anywhere, but it acquires both the spinlock and the Mutex) |
|
|
|
old_h = h; // remember we searched to here |
|
|
|
// Walk the path upto and including h looking for waiters we can wake. |
|
while (pw_walk != h) { |
|
w_walk->wake = false; |
|
if (w_walk->waitp->cond == |
|
nullptr || // no condition => vacuously true OR |
|
(w_walk->waitp->cond != known_false && |
|
// this thread's condition is not known false, AND |
|
// is in fact true |
|
EvalConditionIgnored(this, w_walk->waitp->cond))) { |
|
if (w == nullptr) { |
|
w_walk->wake = true; // can wake this waiter |
|
w = w_walk; |
|
pw = pw_walk; |
|
if (w_walk->waitp->how == kExclusive) { |
|
wr_wait = kMuWrWait; |
|
break; // bail if waking this writer |
|
} |
|
} else if (w_walk->waitp->how == kShared) { // wake if a reader |
|
w_walk->wake = true; |
|
} else { // writer with true condition |
|
wr_wait = kMuWrWait; |
|
} |
|
} else { // can't wake; condition false |
|
known_false = w_walk->waitp->cond; // remember last false condition |
|
} |
|
if (w_walk->wake) { // we're waking reader w_walk |
|
pw_walk = w_walk; // don't skip similar waiters |
|
} else { // not waking; skip as much as possible |
|
pw_walk = Skip(w_walk); |
|
} |
|
// If pw_walk == h, then load of pw_walk->next can race with |
|
// concurrent write in Enqueue(). However, at the same time |
|
// we do not need to do the load, because we will bail out |
|
// from the loop anyway. |
|
if (pw_walk != h) { |
|
w_walk = pw_walk->next; |
|
} |
|
} |
|
|
|
continue; // restart for(;;)-loop to wakeup w or to find more waiters |
|
} |
|
ABSL_RAW_CHECK(pw->next == w, "pw not w's predecessor"); |
|
// The first (and perhaps only) waiter we've chosen to wake is w, whose |
|
// predecessor is pw. If w is a reader, we must wake all the other |
|
// waiters with wake==true as well. We may also need to queue |
|
// ourselves if waitp != null. The spinlock and the lock are still |
|
// held. |
|
|
|
// This traverses the list in [ pw->next, h ], where h is the head, |
|
// removing all elements with wake==true and placing them in the |
|
// singly-linked list wake_list. Returns the new head. |
|
h = DequeueAllWakeable(h, pw, &wake_list); |
|
|
|
intptr_t nv = (v & kMuEvent) | kMuDesig; |
|
// assume no waiters left, |
|
// set kMuDesig for INV1a |
|
|
|
if (waitp != nullptr) { // we must queue ourselves and sleep |
|
h = Enqueue(h, waitp, v, kMuIsCond); |
|
// h is new last waiter; could be null if we queued ourselves on a |
|
// CondVar |
|
} |
|
|
|
ABSL_RAW_CHECK(wake_list != kPerThreadSynchNull, |
|
"unexpected empty wake list"); |
|
|
|
if (h != nullptr) { // there are waiters left |
|
h->readers = 0; |
|
h->maybe_unlocking = false; // finished unlocking |
|
nv |= wr_wait | kMuWait | reinterpret_cast<intptr_t>(h); |
|
} |
|
|
|
// release both spinlock & lock |
|
// can release with a store because there were waiters |
|
mu_.store(nv, std::memory_order_release); |
|
break; // out of for(;;)-loop |
|
} |
|
// aggressive here; no one can proceed till we do |
|
c = synchronization_internal::MutexDelay(c, AGGRESSIVE); |
|
} // end of for(;;)-loop |
|
|
|
if (wake_list != kPerThreadSynchNull) { |
|
int64_t enqueue_timestamp = wake_list->waitp->contention_start_cycles; |
|
bool cond_waiter = wake_list->cond_waiter; |
|
do { |
|
wake_list = Wakeup(wake_list); // wake waiters |
|
} while (wake_list != kPerThreadSynchNull); |
|
if (!cond_waiter) { |
|
// Sample lock contention events only if the (first) waiter was trying to |
|
// acquire the lock, not waiting on a condition variable or Condition. |
|
int64_t wait_cycles = |
|
base_internal::CycleClock::Now() - enqueue_timestamp; |
|
mutex_tracer("slow release", this, wait_cycles); |
|
ABSL_TSAN_MUTEX_PRE_DIVERT(this, 0); |
|
submit_profile_data(enqueue_timestamp); |
|
ABSL_TSAN_MUTEX_POST_DIVERT(this, 0); |
|
} |
|
} |
|
} |
|
|
|
// Used by CondVar implementation to reacquire mutex after waking from |
|
// condition variable. This routine is used instead of Lock() because the |
|
// waiting thread may have been moved from the condition variable queue to the |
|
// mutex queue without a wakeup, by Trans(). In that case, when the thread is |
|
// finally woken, the woken thread will believe it has been woken from the |
|
// condition variable (i.e. its PC will be in when in the CondVar code), when |
|
// in fact it has just been woken from the mutex. Thus, it must enter the slow |
|
// path of the mutex in the same state as if it had just woken from the mutex. |
|
// That is, it must ensure to clear kMuDesig (INV1b). |
|
void Mutex::Trans(MuHow how) { |
|
this->LockSlow(how, nullptr, kMuHasBlocked | kMuIsCond); |
|
} |
|
|
|
// Used by CondVar implementation to effectively wake thread w from the |
|
// condition variable. If this mutex is free, we simply wake the thread. |
|
// It will later acquire the mutex with high probability. Otherwise, we |
|
// enqueue thread w on this mutex. |
|
void Mutex::Fer(PerThreadSynch *w) { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
int c = 0; |
|
ABSL_RAW_CHECK(w->waitp->cond == nullptr, |
|
"Mutex::Fer while waiting on Condition"); |
|
ABSL_RAW_CHECK(!w->waitp->timeout.has_timeout(), |
|
"Mutex::Fer while in timed wait"); |
|
ABSL_RAW_CHECK(w->waitp->cv_word == nullptr, |
|
"Mutex::Fer with pending CondVar queueing"); |
|
for (;;) { |
|
intptr_t v = mu_.load(std::memory_order_relaxed); |
|
// Note: must not queue if the mutex is unlocked (nobody will wake it). |
|
// For example, we can have only kMuWait (conditional) or maybe |
|
// kMuWait|kMuWrWait. |
|
// conflicting != 0 implies that the waking thread cannot currently take |
|
// the mutex, which in turn implies that someone else has it and can wake |
|
// us if we queue. |
|
const intptr_t conflicting = |
|
kMuWriter | (w->waitp->how == kShared ? 0 : kMuReader); |
|
if ((v & conflicting) == 0) { |
|
w->next = nullptr; |
|
w->state.store(PerThreadSynch::kAvailable, std::memory_order_release); |
|
IncrementSynchSem(this, w); |
|
return; |
|
} else { |
|
if ((v & (kMuSpin|kMuWait)) == 0) { // no waiters |
|
// This thread tries to become the one and only waiter. |
|
PerThreadSynch *new_h = Enqueue(nullptr, w->waitp, v, kMuIsCond); |
|
ABSL_RAW_CHECK(new_h != nullptr, |
|
"Enqueue failed"); // we must queue ourselves |
|
if (mu_.compare_exchange_strong( |
|
v, reinterpret_cast<intptr_t>(new_h) | (v & kMuLow) | kMuWait, |
|
std::memory_order_release, std::memory_order_relaxed)) { |
|
return; |
|
} |
|
} else if ((v & kMuSpin) == 0 && |
|
mu_.compare_exchange_strong(v, v | kMuSpin | kMuWait)) { |
|
PerThreadSynch *h = GetPerThreadSynch(v); |
|
PerThreadSynch *new_h = Enqueue(h, w->waitp, v, kMuIsCond); |
|
ABSL_RAW_CHECK(new_h != nullptr, |
|
"Enqueue failed"); // we must queue ourselves |
|
do { |
|
v = mu_.load(std::memory_order_relaxed); |
|
} while (!mu_.compare_exchange_weak( |
|
v, |
|
(v & kMuLow & ~kMuSpin) | kMuWait | |
|
reinterpret_cast<intptr_t>(new_h), |
|
std::memory_order_release, std::memory_order_relaxed)); |
|
return; |
|
} |
|
} |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
} |
|
} |
|
|
|
void Mutex::AssertHeld() const { |
|
if ((mu_.load(std::memory_order_relaxed) & kMuWriter) == 0) { |
|
SynchEvent *e = GetSynchEvent(this); |
|
ABSL_RAW_LOG(FATAL, "thread should hold write lock on Mutex %p %s", |
|
static_cast<const void *>(this), |
|
(e == nullptr ? "" : e->name)); |
|
} |
|
} |
|
|
|
void Mutex::AssertReaderHeld() const { |
|
if ((mu_.load(std::memory_order_relaxed) & (kMuReader | kMuWriter)) == 0) { |
|
SynchEvent *e = GetSynchEvent(this); |
|
ABSL_RAW_LOG( |
|
FATAL, "thread should hold at least a read lock on Mutex %p %s", |
|
static_cast<const void *>(this), (e == nullptr ? "" : e->name)); |
|
} |
|
} |
|
|
|
// -------------------------------- condition variables |
|
static const intptr_t kCvSpin = 0x0001L; // spinlock protects waiter list |
|
static const intptr_t kCvEvent = 0x0002L; // record events |
|
|
|
static const intptr_t kCvLow = 0x0003L; // low order bits of CV |
|
|
|
// Hack to make constant values available to gdb pretty printer |
|
enum { kGdbCvSpin = kCvSpin, kGdbCvEvent = kCvEvent, kGdbCvLow = kCvLow, }; |
|
|
|
static_assert(PerThreadSynch::kAlignment > kCvLow, |
|
"PerThreadSynch::kAlignment must be greater than kCvLow"); |
|
|
|
void CondVar::EnableDebugLog(const char *name) { |
|
SynchEvent *e = EnsureSynchEvent(&this->cv_, name, kCvEvent, kCvSpin); |
|
e->log = true; |
|
UnrefSynchEvent(e); |
|
} |
|
|
|
CondVar::~CondVar() { |
|
if ((cv_.load(std::memory_order_relaxed) & kCvEvent) != 0) { |
|
ForgetSynchEvent(&this->cv_, kCvEvent, kCvSpin); |
|
} |
|
} |
|
|
|
|
|
// Remove thread s from the list of waiters on this condition variable. |
|
void CondVar::Remove(PerThreadSynch *s) { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
intptr_t v; |
|
int c = 0; |
|
for (v = cv_.load(std::memory_order_relaxed);; |
|
v = cv_.load(std::memory_order_relaxed)) { |
|
if ((v & kCvSpin) == 0 && // attempt to acquire spinlock |
|
cv_.compare_exchange_strong(v, v | kCvSpin, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
PerThreadSynch *h = reinterpret_cast<PerThreadSynch *>(v & ~kCvLow); |
|
if (h != nullptr) { |
|
PerThreadSynch *w = h; |
|
while (w->next != s && w->next != h) { // search for thread |
|
w = w->next; |
|
} |
|
if (w->next == s) { // found thread; remove it |
|
w->next = s->next; |
|
if (h == s) { |
|
h = (w == s) ? nullptr : w; |
|
} |
|
s->next = nullptr; |
|
s->state.store(PerThreadSynch::kAvailable, std::memory_order_release); |
|
} |
|
} |
|
// release spinlock |
|
cv_.store((v & kCvEvent) | reinterpret_cast<intptr_t>(h), |
|
std::memory_order_release); |
|
return; |
|
} else { |
|
// try again after a delay |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
} |
|
} |
|
} |
|
|
|
// Queue thread waitp->thread on condition variable word cv_word using |
|
// wait parameters waitp. |
|
// We split this into a separate routine, rather than simply doing it as part |
|
// of WaitCommon(). If we were to queue ourselves on the condition variable |
|
// before calling Mutex::UnlockSlow(), the Mutex code might be re-entered (via |
|
// the logging code, or via a Condition function) and might potentially attempt |
|
// to block this thread. That would be a problem if the thread were already on |
|
// a the condition variable waiter queue. Thus, we use the waitp->cv_word |
|
// to tell the unlock code to call CondVarEnqueue() to queue the thread on the |
|
// condition variable queue just before the mutex is to be unlocked, and (most |
|
// importantly) after any call to an external routine that might re-enter the |
|
// mutex code. |
|
static void CondVarEnqueue(SynchWaitParams *waitp) { |
|
// This thread might be transferred to the Mutex queue by Fer() when |
|
// we are woken. To make sure that is what happens, Enqueue() doesn't |
|
// call CondVarEnqueue() again but instead uses its normal code. We |
|
// must do this before we queue ourselves so that cv_word will be null |
|
// when seen by the dequeuer, who may wish immediately to requeue |
|
// this thread on another queue. |
|
std::atomic<intptr_t> *cv_word = waitp->cv_word; |
|
waitp->cv_word = nullptr; |
|
|
|
intptr_t v = cv_word->load(std::memory_order_relaxed); |
|
int c = 0; |
|
while ((v & kCvSpin) != 0 || // acquire spinlock |
|
!cv_word->compare_exchange_weak(v, v | kCvSpin, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
v = cv_word->load(std::memory_order_relaxed); |
|
} |
|
ABSL_RAW_CHECK(waitp->thread->waitp == nullptr, "waiting when shouldn't be"); |
|
waitp->thread->waitp = waitp; // prepare ourselves for waiting |
|
PerThreadSynch *h = reinterpret_cast<PerThreadSynch *>(v & ~kCvLow); |
|
if (h == nullptr) { // add this thread to waiter list |
|
waitp->thread->next = waitp->thread; |
|
} else { |
|
waitp->thread->next = h->next; |
|
h->next = waitp->thread; |
|
} |
|
waitp->thread->state.store(PerThreadSynch::kQueued, |
|
std::memory_order_relaxed); |
|
cv_word->store((v & kCvEvent) | reinterpret_cast<intptr_t>(waitp->thread), |
|
std::memory_order_release); |
|
} |
|
|
|
bool CondVar::WaitCommon(Mutex *mutex, KernelTimeout t) { |
|
bool rc = false; // return value; true iff we timed-out |
|
|
|
intptr_t mutex_v = mutex->mu_.load(std::memory_order_relaxed); |
|
Mutex::MuHow mutex_how = ((mutex_v & kMuWriter) != 0) ? kExclusive : kShared; |
|
ABSL_TSAN_MUTEX_PRE_UNLOCK(mutex, TsanFlags(mutex_how)); |
|
|
|
// maybe trace this call |
|
intptr_t v = cv_.load(std::memory_order_relaxed); |
|
cond_var_tracer("Wait", this); |
|
if ((v & kCvEvent) != 0) { |
|
PostSynchEvent(this, SYNCH_EV_WAIT); |
|
} |
|
|
|
// Release mu and wait on condition variable. |
|
SynchWaitParams waitp(mutex_how, nullptr, t, mutex, |
|
Synch_GetPerThreadAnnotated(mutex), &cv_); |
|
// UnlockSlow() will call CondVarEnqueue() just before releasing the |
|
// Mutex, thus queuing this thread on the condition variable. See |
|
// CondVarEnqueue() for the reasons. |
|
mutex->UnlockSlow(&waitp); |
|
|
|
// wait for signal |
|
while (waitp.thread->state.load(std::memory_order_acquire) == |
|
PerThreadSynch::kQueued) { |
|
if (!Mutex::DecrementSynchSem(mutex, waitp.thread, t)) { |
|
this->Remove(waitp.thread); |
|
rc = true; |
|
} |
|
} |
|
|
|
ABSL_RAW_CHECK(waitp.thread->waitp != nullptr, "not waiting when should be"); |
|
waitp.thread->waitp = nullptr; // cleanup |
|
|
|
// maybe trace this call |
|
cond_var_tracer("Unwait", this); |
|
if ((v & kCvEvent) != 0) { |
|
PostSynchEvent(this, SYNCH_EV_WAIT_RETURNING); |
|
} |
|
|
|
// From synchronization point of view Wait is unlock of the mutex followed |
|
// by lock of the mutex. We've annotated start of unlock in the beginning |
|
// of the function. Now, finish unlock and annotate lock of the mutex. |
|
// (Trans is effectively lock). |
|
ABSL_TSAN_MUTEX_POST_UNLOCK(mutex, TsanFlags(mutex_how)); |
|
ABSL_TSAN_MUTEX_PRE_LOCK(mutex, TsanFlags(mutex_how)); |
|
mutex->Trans(mutex_how); // Reacquire mutex |
|
ABSL_TSAN_MUTEX_POST_LOCK(mutex, TsanFlags(mutex_how), 0); |
|
return rc; |
|
} |
|
|
|
bool CondVar::WaitWithTimeout(Mutex *mu, absl::Duration timeout) { |
|
return WaitWithDeadline(mu, DeadlineFromTimeout(timeout)); |
|
} |
|
|
|
bool CondVar::WaitWithDeadline(Mutex *mu, absl::Time deadline) { |
|
return WaitCommon(mu, KernelTimeout(deadline)); |
|
} |
|
|
|
void CondVar::Wait(Mutex *mu) { |
|
WaitCommon(mu, KernelTimeout::Never()); |
|
} |
|
|
|
// Wake thread w |
|
// If it was a timed wait, w will be waiting on w->cv |
|
// Otherwise, if it was not a Mutex mutex, w will be waiting on w->sem |
|
// Otherwise, w is transferred to the Mutex mutex via Mutex::Fer(). |
|
void CondVar::Wakeup(PerThreadSynch *w) { |
|
if (w->waitp->timeout.has_timeout() || w->waitp->cvmu == nullptr) { |
|
// The waiting thread only needs to observe "w->state == kAvailable" to be |
|
// released, we must cache "cvmu" before clearing "next". |
|
Mutex *mu = w->waitp->cvmu; |
|
w->next = nullptr; |
|
w->state.store(PerThreadSynch::kAvailable, std::memory_order_release); |
|
Mutex::IncrementSynchSem(mu, w); |
|
} else { |
|
w->waitp->cvmu->Fer(w); |
|
} |
|
} |
|
|
|
void CondVar::Signal() { |
|
SchedulingGuard::ScopedDisable disable_rescheduling; |
|
ABSL_TSAN_MUTEX_PRE_SIGNAL(nullptr, 0); |
|
intptr_t v; |
|
int c = 0; |
|
for (v = cv_.load(std::memory_order_relaxed); v != 0; |
|
v = cv_.load(std::memory_order_relaxed)) { |
|
if ((v & kCvSpin) == 0 && // attempt to acquire spinlock |
|
cv_.compare_exchange_strong(v, v | kCvSpin, |
|
std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
PerThreadSynch *h = reinterpret_cast<PerThreadSynch *>(v & ~kCvLow); |
|
PerThreadSynch *w = nullptr; |
|
if (h != nullptr) { // remove first waiter |
|
w = h->next; |
|
if (w == h) { |
|
h = nullptr; |
|
} else { |
|
h->next = w->next; |
|
} |
|
} |
|
// release spinlock |
|
cv_.store((v & kCvEvent) | reinterpret_cast<intptr_t>(h), |
|
std::memory_order_release); |
|
if (w != nullptr) { |
|
CondVar::Wakeup(w); // wake waiter, if there was one |
|
cond_var_tracer("Signal wakeup", this); |
|
} |
|
if ((v & kCvEvent) != 0) { |
|
PostSynchEvent(this, SYNCH_EV_SIGNAL); |
|
} |
|
ABSL_TSAN_MUTEX_POST_SIGNAL(nullptr, 0); |
|
return; |
|
} else { |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
} |
|
} |
|
ABSL_TSAN_MUTEX_POST_SIGNAL(nullptr, 0); |
|
} |
|
|
|
void CondVar::SignalAll () { |
|
ABSL_TSAN_MUTEX_PRE_SIGNAL(nullptr, 0); |
|
intptr_t v; |
|
int c = 0; |
|
for (v = cv_.load(std::memory_order_relaxed); v != 0; |
|
v = cv_.load(std::memory_order_relaxed)) { |
|
// empty the list if spinlock free |
|
// We do this by simply setting the list to empty using |
|
// compare and swap. We then have the entire list in our hands, |
|
// which cannot be changing since we grabbed it while no one |
|
// held the lock. |
|
if ((v & kCvSpin) == 0 && |
|
cv_.compare_exchange_strong(v, v & kCvEvent, std::memory_order_acquire, |
|
std::memory_order_relaxed)) { |
|
PerThreadSynch *h = reinterpret_cast<PerThreadSynch *>(v & ~kCvLow); |
|
if (h != nullptr) { |
|
PerThreadSynch *w; |
|
PerThreadSynch *n = h->next; |
|
do { // for every thread, wake it up |
|
w = n; |
|
n = n->next; |
|
CondVar::Wakeup(w); |
|
} while (w != h); |
|
cond_var_tracer("SignalAll wakeup", this); |
|
} |
|
if ((v & kCvEvent) != 0) { |
|
PostSynchEvent(this, SYNCH_EV_SIGNALALL); |
|
} |
|
ABSL_TSAN_MUTEX_POST_SIGNAL(nullptr, 0); |
|
return; |
|
} else { |
|
// try again after a delay |
|
c = synchronization_internal::MutexDelay(c, GENTLE); |
|
} |
|
} |
|
ABSL_TSAN_MUTEX_POST_SIGNAL(nullptr, 0); |
|
} |
|
|
|
void ReleasableMutexLock::Release() { |
|
ABSL_RAW_CHECK(this->mu_ != nullptr, |
|
"ReleasableMutexLock::Release may only be called once"); |
|
this->mu_->Unlock(); |
|
this->mu_ = nullptr; |
|
} |
|
|
|
#ifdef ABSL_HAVE_THREAD_SANITIZER |
|
extern "C" void __tsan_read1(void *addr); |
|
#else |
|
#define __tsan_read1(addr) // do nothing if TSan not enabled |
|
#endif |
|
|
|
// A function that just returns its argument, dereferenced |
|
static bool Dereference(void *arg) { |
|
// ThreadSanitizer does not instrument this file for memory accesses. |
|
// This function dereferences a user variable that can participate |
|
// in a data race, so we need to manually tell TSan about this memory access. |
|
__tsan_read1(arg); |
|
return *(static_cast<bool *>(arg)); |
|
} |
|
|
|
Condition::Condition() {} // null constructor, used for kTrue only |
|
const Condition Condition::kTrue; |
|
|
|
Condition::Condition(bool (*func)(void *), void *arg) |
|
: eval_(&CallVoidPtrFunction), |
|
function_(func), |
|
method_(nullptr), |
|
arg_(arg) {} |
|
|
|
bool Condition::CallVoidPtrFunction(const Condition *c) { |
|
return (*c->function_)(c->arg_); |
|
} |
|
|
|
Condition::Condition(const bool *cond) |
|
: eval_(CallVoidPtrFunction), |
|
function_(Dereference), |
|
method_(nullptr), |
|
// const_cast is safe since Dereference does not modify arg |
|
arg_(const_cast<bool *>(cond)) {} |
|
|
|
bool Condition::Eval() const { |
|
// eval_ == null for kTrue |
|
return (this->eval_ == nullptr) || (*this->eval_)(this); |
|
} |
|
|
|
bool Condition::GuaranteedEqual(const Condition *a, const Condition *b) { |
|
if (a == nullptr) { |
|
return b == nullptr || b->eval_ == nullptr; |
|
} |
|
if (b == nullptr || b->eval_ == nullptr) { |
|
return a->eval_ == nullptr; |
|
} |
|
return a->eval_ == b->eval_ && a->function_ == b->function_ && |
|
a->arg_ == b->arg_ && a->method_ == b->method_; |
|
} |
|
|
|
ABSL_NAMESPACE_END |
|
} // namespace absl
|
|
|