THUAI6/CAPI/cpp/grpc/include/absl/synchronization/internal/thread_pool.h

// 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 <vector>

#include "absl/base/thread_annotations.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)
            {
                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(std::function<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)
                {
                    std::function<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<std::function<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_