Abseil Common Libraries (C++) (grcp 依赖)
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161 lines
5.2 KiB
161 lines
5.2 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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// |
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#ifndef ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_ |
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#define 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 <sdkddkver.h> |
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#else |
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#include <pthread.h> |
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#endif |
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#ifdef __linux__ |
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#include <linux/futex.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 <atomic> |
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#include <cstdint> |
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#include "absl/base/internal/thread_identity.h" |
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#include "absl/synchronization/internal/futex.h" |
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#include "absl/synchronization/internal/kernel_timeout.h" |
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// May be chosen at compile time via -DABSL_FORCE_WAITER_MODE=<index> |
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#define ABSL_WAITER_MODE_FUTEX 0 |
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#define ABSL_WAITER_MODE_SEM 1 |
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#define ABSL_WAITER_MODE_CONDVAR 2 |
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#define ABSL_WAITER_MODE_WIN32 3 |
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#if defined(ABSL_FORCE_WAITER_MODE) |
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#define ABSL_WAITER_MODE ABSL_FORCE_WAITER_MODE |
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#elif defined(_WIN32) && _WIN32_WINNT >= _WIN32_WINNT_VISTA |
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#define ABSL_WAITER_MODE ABSL_WAITER_MODE_WIN32 |
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#elif defined(ABSL_INTERNAL_HAVE_FUTEX) |
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#define ABSL_WAITER_MODE ABSL_WAITER_MODE_FUTEX |
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#elif defined(ABSL_HAVE_SEMAPHORE_H) |
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#define ABSL_WAITER_MODE ABSL_WAITER_MODE_SEM |
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#else |
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#define ABSL_WAITER_MODE ABSL_WAITER_MODE_CONDVAR |
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#endif |
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namespace absl { |
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ABSL_NAMESPACE_BEGIN |
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namespace synchronization_internal { |
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// Waiter is an OS-specific semaphore. |
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class Waiter { |
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public: |
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// Prepare any data to track waits. |
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Waiter(); |
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// Not copyable or movable |
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Waiter(const Waiter&) = delete; |
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Waiter& operator=(const Waiter&) = delete; |
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// Blocks the calling thread until a matching call to `Post()` or |
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// `t` has passed. Returns `true` if woken (`Post()` called), |
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// `false` on timeout. |
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bool Wait(KernelTimeout t); |
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// Restart the caller of `Wait()` as with a normal semaphore. |
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void Post(); |
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// If anyone is waiting, wake them up temporarily and cause them to |
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// call `MaybeBecomeIdle()`. They will then return to waiting for a |
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// `Post()` or timeout. |
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void Poke(); |
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// Returns the Waiter associated with the identity. |
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static Waiter* GetWaiter(base_internal::ThreadIdentity* identity) { |
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static_assert( |
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sizeof(Waiter) <= sizeof(base_internal::ThreadIdentity::WaiterState), |
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"Insufficient space for Waiter"); |
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return reinterpret_cast<Waiter*>(identity->waiter_state.data); |
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} |
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// How many periods to remain idle before releasing resources |
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#ifndef ABSL_HAVE_THREAD_SANITIZER |
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static constexpr int kIdlePeriods = 60; |
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#else |
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// Memory consumption under ThreadSanitizer is a serious concern, |
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// so we release resources sooner. The value of 1 leads to 1 to 2 second |
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// delay before marking a thread as idle. |
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static const int kIdlePeriods = 1; |
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#endif |
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private: |
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// The destructor must not be called since Mutex/CondVar |
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// can use PerThreadSem/Waiter after the thread exits. |
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// Waiter objects are embedded in ThreadIdentity objects, |
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// which are reused via a freelist and are never destroyed. |
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~Waiter() = delete; |
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#if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX |
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// Futexes are defined by specification to be 32-bits. |
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// Thus std::atomic<int32_t> must be just an int32_t with lockfree methods. |
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std::atomic<int32_t> futex_; |
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static_assert(sizeof(int32_t) == sizeof(futex_), "Wrong size for futex"); |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_CONDVAR |
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// REQUIRES: mu_ must be held. |
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void InternalCondVarPoke(); |
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pthread_mutex_t mu_; |
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pthread_cond_t cv_; |
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int waiter_count_; |
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int wakeup_count_; // Unclaimed wakeups. |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_SEM |
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sem_t sem_; |
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// This seems superfluous, but for Poke() we need to cause spurious |
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// wakeups on the semaphore. Hence we can't actually use the |
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// semaphore's count. |
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std::atomic<int> wakeups_; |
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#elif ABSL_WAITER_MODE == ABSL_WAITER_MODE_WIN32 |
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// WinHelper - Used to define utilities for accessing the lock and |
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// condition variable storage once the types are complete. |
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class WinHelper; |
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// REQUIRES: WinHelper::GetLock(this) must be held. |
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void InternalCondVarPoke(); |
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// We can't include Windows.h in our headers, so we use aligned character |
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// buffers to define the storage of SRWLOCK and CONDITION_VARIABLE. |
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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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alignas(void*) unsigned char mu_storage_[sizeof(void*)]; |
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alignas(void*) unsigned char cv_storage_[sizeof(void*)]; |
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int waiter_count_; |
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int wakeup_count_; |
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#else |
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#error Unknown ABSL_WAITER_MODE |
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#endif |
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}; |
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} // namespace synchronization_internal |
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ABSL_NAMESPACE_END |
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} // namespace absl |
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#endif // ABSL_SYNCHRONIZATION_INTERNAL_WAITER_H_
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