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authorDerek Mauro <dmauro@google.com>2023-03-20 14:10:11 -0700
committerCopybara-Service <copybara-worker@google.com>2023-03-20 14:11:09 -0700
commit396e9764cded739f595ba880b95b061051c49128 (patch)
tree02b550c2a2b9a4fcacb4cf2555d9d8672d53248b /absl/synchronization/internal/sem_waiter.cc
parente5067964adcb792b7c9dbddbdcfe4d9b94079597 (diff)
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Synchronization: Refactor Waiter to allow us to write tests
Instead of being only able to test the platform Waiter implementation, this allows us to be able to test all Waiter implementations that build on a specific platform. A unittest is added that tests all implementations that work for the platform, and allows us to check that the expected one is being used by printing the name of the selected implementation. PiperOrigin-RevId: 518072415 Change-Id: Ie9e6fcd9d8283b4038e6f4e68a304d2adcc04b19
Diffstat (limited to 'absl/synchronization/internal/sem_waiter.cc')
-rw-r--r--absl/synchronization/internal/sem_waiter.cc104
1 files changed, 104 insertions, 0 deletions
diff --git a/absl/synchronization/internal/sem_waiter.cc b/absl/synchronization/internal/sem_waiter.cc
new file mode 100644
index 00000000..89af5de2
--- /dev/null
+++ b/absl/synchronization/internal/sem_waiter.cc
@@ -0,0 +1,104 @@
+// Copyright 2023 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/synchronization/internal/sem_waiter.h"
+
+#ifdef ABSL_INTERNAL_HAVE_SEM_WAITER
+
+#include <semaphore.h>
+
+#include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <cerrno>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/thread_identity.h"
+#include "absl/base/optimization.h"
+#include "absl/synchronization/internal/kernel_timeout.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace synchronization_internal {
+
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+constexpr char SemWaiter::kName[];
+#endif
+
+SemWaiter::SemWaiter() : wakeups_(0) {
+ if (sem_init(&sem_, 0, 0) != 0) {
+ ABSL_RAW_LOG(FATAL, "sem_init failed with errno %d\n", errno);
+ }
+}
+
+bool SemWaiter::Wait(KernelTimeout t) {
+ struct timespec abs_timeout;
+ if (t.has_timeout()) {
+ abs_timeout = t.MakeAbsTimespec();
+ }
+
+ // Loop until we timeout or consume a wakeup.
+ // Note that, since the thread ticker is just reset, we don't need to check
+ // whether the thread is idle on the very first pass of the loop.
+ bool first_pass = true;
+ while (true) {
+ int x = wakeups_.load(std::memory_order_relaxed);
+ while (x != 0) {
+ if (!wakeups_.compare_exchange_weak(x, x - 1,
+ std::memory_order_acquire,
+ std::memory_order_relaxed)) {
+ continue; // Raced with someone, retry.
+ }
+ // Successfully consumed a wakeup, we're done.
+ return true;
+ }
+
+ if (!first_pass) MaybeBecomeIdle();
+ // Nothing to consume, wait (looping on EINTR).
+ while (true) {
+ if (!t.has_timeout()) {
+ if (sem_wait(&sem_) == 0) break;
+ if (errno == EINTR) continue;
+ ABSL_RAW_LOG(FATAL, "sem_wait failed: %d", errno);
+ } else {
+ if (sem_timedwait(&sem_, &abs_timeout) == 0) break;
+ if (errno == EINTR) continue;
+ if (errno == ETIMEDOUT) return false;
+ ABSL_RAW_LOG(FATAL, "sem_timedwait failed: %d", errno);
+ }
+ }
+ first_pass = false;
+ }
+}
+
+void SemWaiter::Post() {
+ // Post a wakeup.
+ if (wakeups_.fetch_add(1, std::memory_order_release) == 0) {
+ // We incremented from 0, need to wake a potential waiter.
+ Poke();
+ }
+}
+
+void SemWaiter::Poke() {
+ if (sem_post(&sem_) != 0) { // Wake any semaphore waiter.
+ ABSL_RAW_LOG(FATAL, "sem_post failed with errno %d\n", errno);
+ }
+}
+
+} // namespace synchronization_internal
+ABSL_NAMESPACE_END
+} // namespace absl
+
+#endif // ABSL_INTERNAL_HAVE_SEM_WAITER