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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
//
// 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.
#ifndef ABSL_SYNCHRONIZATION_INTERNAL_THREAD_POOL_H_
#define ABSL_SYNCHRONIZATION_INTERNAL_THREAD_POOL_H_
#include <cassert>
#include <cstddef>
#include <functional>
#include <queue>
#include <thread> // NOLINT(build/c++11)
#include <utility>
#include <vector>
#include "absl/base/thread_annotations.h"
#include "absl/functional/any_invocable.h"
#include "absl/synchronization/mutex.h"
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace synchronization_internal {
// A simple ThreadPool implementation for tests.
class ThreadPool {
public:
explicit ThreadPool(int num_threads) {
threads_.reserve(num_threads);
for (int i = 0; i < num_threads; ++i) {
threads_.push_back(std::thread(&ThreadPool::WorkLoop, this));
}
}
ThreadPool(const ThreadPool &) = delete;
ThreadPool &operator=(const ThreadPool &) = delete;
~ThreadPool() {
{
absl::MutexLock l(&mu_);
for (size_t i = 0; i < threads_.size(); i++) {
queue_.push(nullptr); // Shutdown signal.
}
}
for (auto &t : threads_) {
t.join();
}
}
// Schedule a function to be run on a ThreadPool thread immediately.
void Schedule(absl::AnyInvocable<void()> func) {
assert(func != nullptr);
absl::MutexLock l(&mu_);
queue_.push(std::move(func));
}
private:
bool WorkAvailable() const ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu_) {
return !queue_.empty();
}
void WorkLoop() {
while (true) {
absl::AnyInvocable<void()> func;
{
absl::MutexLock l(&mu_);
mu_.Await(absl::Condition(this, &ThreadPool::WorkAvailable));
func = std::move(queue_.front());
queue_.pop();
}
if (func == nullptr) { // Shutdown signal.
break;
}
func();
}
}
absl::Mutex mu_;
std::queue<absl::AnyInvocable<void()>> queue_ ABSL_GUARDED_BY(mu_);
std::vector<std::thread> threads_;
};
} // namespace synchronization_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif // ABSL_SYNCHRONIZATION_INTERNAL_THREAD_POOL_H_
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