fc8dc48020
git-subtree-dir: third_party/abseil_cpp git-subtree-mainline:ffb2ae54begit-subtree-split:768eb2ca28
159 lines
4.9 KiB
C++
159 lines
4.9 KiB
C++
// 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/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(__BIONIC__)
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// Bionic supports all the futex operations we need even when some of the futex
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// definitions are missing.
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#define ABSL_WAITER_MODE ABSL_WAITER_MODE_FUTEX
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#elif defined(__linux__) && defined(FUTEX_CLOCK_REALTIME)
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// FUTEX_CLOCK_REALTIME requires Linux >= 2.6.28.
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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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// Destroy any data to track waits.
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~Waiter();
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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 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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#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 charachter
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// buffers to define the storage of SRWLOCK and CONDITION_VARIABLE.
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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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