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// Copyright 2017 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
//
// http://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.
// This file is a no-op if the required LowLevelAlloc support is missing.
#include "absl/base/internal/low_level_alloc.h"
#ifndef ABSL_LOW_LEVEL_ALLOC_MISSING
#include "absl/synchronization/internal/per_thread_sem.h"
#include <atomic>
#include "absl/base/attributes.h"
#include "absl/base/internal/malloc_extension.h"
#include "absl/base/internal/thread_identity.h"
#include "absl/synchronization/internal/waiter.h"
namespace absl {
namespace synchronization_internal {
void PerThreadSem::SetThreadBlockedCounter(std::atomic<int> *counter) {
base_internal::ThreadIdentity *identity;
identity = GetOrCreateCurrentThreadIdentity();
identity->blocked_count_ptr = counter;
}
std::atomic<int> *PerThreadSem::GetThreadBlockedCounter() {
base_internal::ThreadIdentity *identity;
identity = GetOrCreateCurrentThreadIdentity();
return identity->blocked_count_ptr;
}
void PerThreadSem::Init(base_internal::ThreadIdentity *identity) {
Waiter::GetWaiter(identity)->Init();
identity->ticker.store(0, std::memory_order_relaxed);
identity->wait_start.store(0, std::memory_order_relaxed);
identity->is_idle.store(false, std::memory_order_relaxed);
}
void PerThreadSem::Tick(base_internal::ThreadIdentity *identity) {
const int ticker =
identity->ticker.fetch_add(1, std::memory_order_relaxed) + 1;
const int wait_start = identity->wait_start.load(std::memory_order_relaxed);
const bool is_idle = identity->is_idle.load(std::memory_order_relaxed);
if (wait_start && (ticker - wait_start > Waiter::kIdlePeriods) && !is_idle) {
// Wakeup the waiting thread since it is time for it to become idle.
Waiter::GetWaiter(identity)->Poke();
}
}
} // namespace synchronization_internal
} // namespace absl
extern "C" {
ABSL_ATTRIBUTE_WEAK void AbslInternalPerThreadSemPost(
absl::base_internal::ThreadIdentity *identity) {
absl::synchronization_internal::Waiter::GetWaiter(identity)->Post();
}
ABSL_ATTRIBUTE_WEAK bool AbslInternalPerThreadSemWait(
absl::synchronization_internal::KernelTimeout t) {
bool timeout = false;
absl::base_internal::ThreadIdentity *identity;
identity = absl::synchronization_internal::GetOrCreateCurrentThreadIdentity();
// Ensure wait_start != 0.
int ticker = identity->ticker.load(std::memory_order_relaxed);
identity->wait_start.store(ticker ? ticker : 1, std::memory_order_relaxed);
identity->is_idle.store(false, std::memory_order_relaxed);
if (identity->blocked_count_ptr != nullptr) {
// Increment count of threads blocked in a given thread pool.
identity->blocked_count_ptr->fetch_add(1, std::memory_order_relaxed);
}
timeout =
!absl::synchronization_internal::Waiter::GetWaiter(identity)->Wait(t);
if (identity->blocked_count_ptr != nullptr) {
identity->blocked_count_ptr->fetch_sub(1, std::memory_order_relaxed);
}
if (identity->is_idle.load(std::memory_order_relaxed)) {
// We became idle during the wait; become non-idle again so that
// performance of deallocations done from now on does not suffer.
absl::base_internal::MallocExtension::instance()->MarkThreadBusy();
}
identity->is_idle.store(false, std::memory_order_relaxed);
identity->wait_start.store(0, std::memory_order_relaxed);
return !timeout;
}
} // extern "C"
#endif // ABSL_LOW_LEVEL_ALLOC_MISSING
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