Abseil Common Libraries (C++) (grcp 依赖)
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484 lines
14 KiB
484 lines
14 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/internal/waiter.h" |
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#include "absl/base/config.h" |
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#ifdef _WIN32 |
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#include <windows.h> |
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#else |
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#include <pthread.h> |
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#include <sys/time.h> |
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#include <unistd.h> |
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#endif |
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#ifdef __linux__ |
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#include <linux/futex.h> |
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#include <sys/syscall.h> |
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#endif |
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#ifdef ABSL_HAVE_SEMAPHORE_H |
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#include <semaphore.h> |
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#endif |
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#include <errno.h> |
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#include <stdio.h> |
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#include <time.h> |
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#include <atomic> |
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#include <cassert> |
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#include <cstdint> |
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#include <new> |
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#include <type_traits> |
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#include "absl/base/internal/raw_logging.h" |
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#include "absl/base/internal/thread_identity.h" |
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#include "absl/base/optimization.h" |
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#include "absl/synchronization/internal/kernel_timeout.h" |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace synchronization_internal { |
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static void MaybeBecomeIdle() { |
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base_internal::ThreadIdentity *identity = |
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base_internal::CurrentThreadIdentityIfPresent(); |
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assert(identity != nullptr); |
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const bool is_idle = identity->is_idle.load(std::memory_order_relaxed); |
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const int ticker = identity->ticker.load(std::memory_order_relaxed); |
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const int wait_start = identity->wait_start.load(std::memory_order_relaxed); |
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if (!is_idle && ticker - wait_start > Waiter::kIdlePeriods) { |
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identity->is_idle.store(true, std::memory_order_relaxed); |
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} |
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} |
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#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX |
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// Some Android headers are missing these definitions even though they |
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// support these futex operations. |
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#ifdef __BIONIC__ |
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#ifndef SYS_futex |
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#define SYS_futex __NR_futex |
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#endif |
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#ifndef FUTEX_WAIT_BITSET |
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#define FUTEX_WAIT_BITSET 9 |
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#endif |
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#ifndef FUTEX_PRIVATE_FLAG |
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#define FUTEX_PRIVATE_FLAG 128 |
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#endif |
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#ifndef FUTEX_CLOCK_REALTIME |
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#define FUTEX_CLOCK_REALTIME 256 |
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#endif |
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#ifndef FUTEX_BITSET_MATCH_ANY |
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#define FUTEX_BITSET_MATCH_ANY 0xFFFFFFFF |
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#endif |
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#endif |
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class Futex { |
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public: |
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static int WaitUntil(std::atomic<int32_t> *v, int32_t val, |
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KernelTimeout t) { |
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int err = 0; |
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if (t.has_timeout()) { |
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// https://locklessinc.com/articles/futex_cheat_sheet/ |
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// Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time. |
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struct timespec abs_timeout = t.MakeAbsTimespec(); |
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// Atomically check that the futex value is still 0, and if it |
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// is, sleep until abs_timeout or until woken by FUTEX_WAKE. |
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err = syscall( |
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SYS_futex, reinterpret_cast<int32_t *>(v), |
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FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, val, |
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&abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY); |
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} else { |
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// Atomically check that the futex value is still 0, and if it |
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// is, sleep until woken by FUTEX_WAKE. |
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err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v), |
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FUTEX_WAIT | FUTEX_PRIVATE_FLAG, val, nullptr); |
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} |
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if (err != 0) { |
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err = -errno; |
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} |
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return err; |
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} |
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static int Wake(std::atomic<int32_t> *v, int32_t count) { |
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int err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v), |
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FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count); |
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if (ABSL_PREDICT_FALSE(err < 0)) { |
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err = -errno; |
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} |
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return err; |
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} |
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}; |
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Waiter::Waiter() { |
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futex_.store(0, std::memory_order_relaxed); |
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} |
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Waiter::~Waiter() = default; |
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bool Waiter::Wait(KernelTimeout t) { |
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// Loop until we can atomically decrement futex from a positive |
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// value, waiting on a futex while we believe it is zero. |
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// Note that, since the thread ticker is just reset, we don't need to check |
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// whether the thread is idle on the very first pass of the loop. |
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bool first_pass = true; |
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while (true) { |
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int32_t x = futex_.load(std::memory_order_relaxed); |
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while (x != 0) { |
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if (!futex_.compare_exchange_weak(x, x - 1, |
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std::memory_order_acquire, |
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std::memory_order_relaxed)) { |
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continue; // Raced with someone, retry. |
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} |
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return true; // Consumed a wakeup, we are done. |
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} |
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if (!first_pass) MaybeBecomeIdle(); |
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const int err = Futex::WaitUntil(&futex_, 0, t); |
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if (err != 0) { |
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if (err == -EINTR || err == -EWOULDBLOCK) { |
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// Do nothing, the loop will retry. |
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} else if (err == -ETIMEDOUT) { |
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return false; |
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} else { |
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ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err); |
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} |
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} |
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first_pass = false; |
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} |
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} |
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void Waiter::Post() { |
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if (futex_.fetch_add(1, std::memory_order_release) == 0) { |
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// We incremented from 0, need to wake a potential waiter. |
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Poke(); |
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} |
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} |
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void Waiter::Poke() { |
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// Wake one thread waiting on the futex. |
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const int err = Futex::Wake(&futex_, 1); |
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if (ABSL_PREDICT_FALSE(err < 0)) { |
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ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err); |
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} |
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} |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_CONDVAR |
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class PthreadMutexHolder { |
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public: |
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explicit PthreadMutexHolder(pthread_mutex_t *mu) : mu_(mu) { |
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const int err = pthread_mutex_lock(mu_); |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_mutex_lock failed: %d", err); |
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} |
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} |
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PthreadMutexHolder(const PthreadMutexHolder &rhs) = delete; |
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PthreadMutexHolder &operator=(const PthreadMutexHolder &rhs) = delete; |
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~PthreadMutexHolder() { |
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const int err = pthread_mutex_unlock(mu_); |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_mutex_unlock failed: %d", err); |
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} |
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} |
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private: |
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pthread_mutex_t *mu_; |
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}; |
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Waiter::Waiter() { |
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const int err = pthread_mutex_init(&mu_, 0); |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_mutex_init failed: %d", err); |
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} |
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const int err2 = pthread_cond_init(&cv_, 0); |
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if (err2 != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_cond_init failed: %d", err2); |
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} |
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waiter_count_ = 0; |
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wakeup_count_ = 0; |
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} |
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Waiter::~Waiter() { |
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const int err = pthread_mutex_destroy(&mu_); |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_mutex_destroy failed: %d", err); |
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} |
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const int err2 = pthread_cond_destroy(&cv_); |
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if (err2 != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_cond_destroy failed: %d", err2); |
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} |
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} |
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bool Waiter::Wait(KernelTimeout t) { |
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struct timespec abs_timeout; |
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if (t.has_timeout()) { |
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abs_timeout = t.MakeAbsTimespec(); |
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} |
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PthreadMutexHolder h(&mu_); |
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++waiter_count_; |
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// Loop until we find a wakeup to consume or timeout. |
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// Note that, since the thread ticker is just reset, we don't need to check |
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// whether the thread is idle on the very first pass of the loop. |
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bool first_pass = true; |
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while (wakeup_count_ == 0) { |
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if (!first_pass) MaybeBecomeIdle(); |
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// No wakeups available, time to wait. |
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if (!t.has_timeout()) { |
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const int err = pthread_cond_wait(&cv_, &mu_); |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_cond_wait failed: %d", err); |
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} |
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} else { |
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const int err = pthread_cond_timedwait(&cv_, &mu_, &abs_timeout); |
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if (err == ETIMEDOUT) { |
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--waiter_count_; |
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return false; |
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} |
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if (err != 0) { |
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ABSL_RAW_LOG(FATAL, "pthread_cond_timedwait failed: %d", err); |
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} |
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} |
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first_pass = false; |
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} |
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// Consume a wakeup and we're done. |
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--wakeup_count_; |
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--waiter_count_; |
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return true; |
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} |
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void Waiter::Post() { |
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PthreadMutexHolder h(&mu_); |
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++wakeup_count_; |
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InternalCondVarPoke(); |
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} |
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void Waiter::Poke() { |
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PthreadMutexHolder h(&mu_); |
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InternalCondVarPoke(); |
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} |
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void Waiter::InternalCondVarPoke() { |
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if (waiter_count_ != 0) { |
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const int err = pthread_cond_signal(&cv_); |
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if (ABSL_PREDICT_FALSE(err != 0)) { |
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ABSL_RAW_LOG(FATAL, "pthread_cond_signal failed: %d", err); |
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} |
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} |
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} |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_SEM |
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Waiter::Waiter() { |
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if (sem_init(&sem_, 0, 0) != 0) { |
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ABSL_RAW_LOG(FATAL, "sem_init failed with errno %d\n", errno); |
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} |
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wakeups_.store(0, std::memory_order_relaxed); |
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} |
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Waiter::~Waiter() { |
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if (sem_destroy(&sem_) != 0) { |
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ABSL_RAW_LOG(FATAL, "sem_destroy failed with errno %d\n", errno); |
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} |
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} |
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bool Waiter::Wait(KernelTimeout t) { |
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struct timespec abs_timeout; |
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if (t.has_timeout()) { |
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abs_timeout = t.MakeAbsTimespec(); |
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} |
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// Loop until we timeout or consume a wakeup. |
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// Note that, since the thread ticker is just reset, we don't need to check |
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// whether the thread is idle on the very first pass of the loop. |
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bool first_pass = true; |
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while (true) { |
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int x = wakeups_.load(std::memory_order_relaxed); |
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while (x != 0) { |
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if (!wakeups_.compare_exchange_weak(x, x - 1, |
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std::memory_order_acquire, |
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std::memory_order_relaxed)) { |
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continue; // Raced with someone, retry. |
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} |
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// Successfully consumed a wakeup, we're done. |
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return true; |
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} |
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if (!first_pass) MaybeBecomeIdle(); |
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// Nothing to consume, wait (looping on EINTR). |
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while (true) { |
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if (!t.has_timeout()) { |
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if (sem_wait(&sem_) == 0) break; |
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if (errno == EINTR) continue; |
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ABSL_RAW_LOG(FATAL, "sem_wait failed: %d", errno); |
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} else { |
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if (sem_timedwait(&sem_, &abs_timeout) == 0) break; |
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if (errno == EINTR) continue; |
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if (errno == ETIMEDOUT) return false; |
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ABSL_RAW_LOG(FATAL, "sem_timedwait failed: %d", errno); |
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} |
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} |
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first_pass = false; |
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} |
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} |
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void Waiter::Post() { |
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// Post a wakeup. |
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if (wakeups_.fetch_add(1, std::memory_order_release) == 0) { |
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// We incremented from 0, need to wake a potential waiter. |
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Poke(); |
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} |
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} |
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void Waiter::Poke() { |
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if (sem_post(&sem_) != 0) { // Wake any semaphore waiter. |
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ABSL_RAW_LOG(FATAL, "sem_post failed with errno %d\n", errno); |
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} |
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} |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_WIN32 |
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class Waiter::WinHelper { |
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public: |
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static SRWLOCK *GetLock(Waiter *w) { |
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return reinterpret_cast<SRWLOCK *>(&w->mu_storage_); |
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} |
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static CONDITION_VARIABLE *GetCond(Waiter *w) { |
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return reinterpret_cast<CONDITION_VARIABLE *>(&w->cv_storage_); |
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} |
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static_assert(sizeof(SRWLOCK) == sizeof(void *), |
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"`mu_storage_` does not have the same size as SRWLOCK"); |
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static_assert(alignof(SRWLOCK) == alignof(void *), |
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"`mu_storage_` does not have the same alignment as SRWLOCK"); |
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static_assert(sizeof(CONDITION_VARIABLE) == sizeof(void *), |
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"`ABSL_CONDITION_VARIABLE_STORAGE` does not have the same size " |
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"as `CONDITION_VARIABLE`"); |
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static_assert( |
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alignof(CONDITION_VARIABLE) == alignof(void *), |
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"`cv_storage_` does not have the same alignment as `CONDITION_VARIABLE`"); |
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// The SRWLOCK and CONDITION_VARIABLE types must be trivially constructible |
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// and destructible because we never call their constructors or destructors. |
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static_assert(std::is_trivially_constructible<SRWLOCK>::value, |
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"The `SRWLOCK` type must be trivially constructible"); |
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static_assert( |
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std::is_trivially_constructible<CONDITION_VARIABLE>::value, |
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"The `CONDITION_VARIABLE` type must be trivially constructible"); |
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static_assert(std::is_trivially_destructible<SRWLOCK>::value, |
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"The `SRWLOCK` type must be trivially destructible"); |
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static_assert(std::is_trivially_destructible<CONDITION_VARIABLE>::value, |
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"The `CONDITION_VARIABLE` type must be trivially destructible"); |
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}; |
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class LockHolder { |
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public: |
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explicit LockHolder(SRWLOCK* mu) : mu_(mu) { |
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AcquireSRWLockExclusive(mu_); |
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} |
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LockHolder(const LockHolder&) = delete; |
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LockHolder& operator=(const LockHolder&) = delete; |
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~LockHolder() { |
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ReleaseSRWLockExclusive(mu_); |
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} |
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private: |
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SRWLOCK* mu_; |
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}; |
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Waiter::Waiter() { |
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auto *mu = ::new (static_cast<void *>(&mu_storage_)) SRWLOCK; |
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auto *cv = ::new (static_cast<void *>(&cv_storage_)) CONDITION_VARIABLE; |
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InitializeSRWLock(mu); |
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InitializeConditionVariable(cv); |
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waiter_count_ = 0; |
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wakeup_count_ = 0; |
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} |
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// SRW locks and condition variables do not need to be explicitly destroyed. |
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// https://docs.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-initializesrwlock |
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// https://stackoverflow.com/questions/28975958/why-does-windows-have-no-deleteconditionvariable-function-to-go-together-with |
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Waiter::~Waiter() = default; |
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bool Waiter::Wait(KernelTimeout t) { |
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SRWLOCK *mu = WinHelper::GetLock(this); |
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CONDITION_VARIABLE *cv = WinHelper::GetCond(this); |
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LockHolder h(mu); |
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++waiter_count_; |
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// Loop until we find a wakeup to consume or timeout. |
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// Note that, since the thread ticker is just reset, we don't need to check |
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// whether the thread is idle on the very first pass of the loop. |
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bool first_pass = true; |
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while (wakeup_count_ == 0) { |
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if (!first_pass) MaybeBecomeIdle(); |
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// No wakeups available, time to wait. |
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if (!SleepConditionVariableSRW(cv, mu, t.InMillisecondsFromNow(), 0)) { |
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// GetLastError() returns a Win32 DWORD, but we assign to |
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// unsigned long to simplify the ABSL_RAW_LOG case below. The uniform |
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// initialization guarantees this is not a narrowing conversion. |
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const unsigned long err{GetLastError()}; // NOLINT(runtime/int) |
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if (err == ERROR_TIMEOUT) { |
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--waiter_count_; |
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return false; |
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} else { |
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ABSL_RAW_LOG(FATAL, "SleepConditionVariableSRW failed: %lu", err); |
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} |
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} |
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first_pass = false; |
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} |
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// Consume a wakeup and we're done. |
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--wakeup_count_; |
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--waiter_count_; |
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return true; |
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} |
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void Waiter::Post() { |
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LockHolder h(WinHelper::GetLock(this)); |
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++wakeup_count_; |
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InternalCondVarPoke(); |
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} |
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void Waiter::Poke() { |
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LockHolder h(WinHelper::GetLock(this)); |
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InternalCondVarPoke(); |
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} |
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void Waiter::InternalCondVarPoke() { |
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if (waiter_count_ != 0) { |
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WakeConditionVariable(WinHelper::GetCond(this)); |
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} |
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} |
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#else |
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#error Unknown ABSL_WAITER_MODE |
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#endif |
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} // namespace synchronization_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl
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