123 lines
3.8 KiB
C++
123 lines
3.8 KiB
C++
// Copyright 2023 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/sem_waiter.h"
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#ifdef ABSL_INTERNAL_HAVE_SEM_WAITER
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#include <semaphore.h>
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#include <atomic>
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#include <cassert>
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#include <cstdint>
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#include <cerrno>
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#include "absl/base/config.h"
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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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#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
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constexpr char SemWaiter::kName[];
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#endif
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SemWaiter::SemWaiter() : wakeups_(0) {
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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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}
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#if defined(__GLIBC__) && \
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(__GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 30))
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#define ABSL_INTERNAL_HAVE_SEM_CLOCKWAIT 1
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#elif defined(__ANDROID_API__) && __ANDROID_API__ >= 30
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#define ABSL_INTERNAL_HAVE_SEM_CLOCKWAIT 1
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#endif
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// Calls sem_timedwait() or possibly something else like
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// sem_clockwait() depending on the platform and
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// KernelTimeout requested. The return value is the same as a call to the return
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// value to a call to sem_timedwait().
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int SemWaiter::TimedWait(KernelTimeout t) {
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if (KernelTimeout::SupportsSteadyClock() && t.is_relative_timeout()) {
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#if defined(ABSL_INTERNAL_HAVE_SEM_CLOCKWAIT) && defined(CLOCK_MONOTONIC)
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const auto abs_clock_timeout = t.MakeClockAbsoluteTimespec(CLOCK_MONOTONIC);
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return sem_clockwait(&sem_, CLOCK_MONOTONIC, &abs_clock_timeout);
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#endif
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}
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const auto abs_timeout = t.MakeAbsTimespec();
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return sem_timedwait(&sem_, &abs_timeout);
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}
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bool SemWaiter::Wait(KernelTimeout t) {
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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 (TimedWait(t) == 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, "SemWaiter::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 SemWaiter::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 SemWaiter::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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} // namespace synchronization_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_INTERNAL_HAVE_SEM_WAITER
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