pytorch源码解析之--线程池实现（线程池专项，包含生产者-消费者模式）

 

#ifndef THREAD_POOL_H
#define THREAD_POOL_H

#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>

class ThreadPool {
public:
    ThreadPool(size_t);
    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args)
        -> std::future<typename std::result_of<F(Args...)>::type>;
    void enqueue(std::function<void()> func);
    ~ThreadPool();

    size_t size() const;
    size_t numAvailable() const;
    bool inThreadPool() const;
    void run(std::function<void()> func);
private:
    // need to keep track of threads so we can join them
    std::vector< std::thread > workers;
    // the task queue
    std::queue< std::function<void()> > tasks;
    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
    size_t available_;
    void main_loop();
};

 

 

// the constructor just launches some amount of workers
inline ThreadPool::ThreadPool(size_t threads)
    :   stop(false)
{
    for(size_t i = 0;i<threads;++i)
        workers.emplace_back(
            [this]
            {
                while (!this->stop) {
                    std::function<void()> task;

                    {
                        std::unique_lock<std::mutex> lock(this->queue_mutex);
                        this->condition.wait(lock,
                            [this]{ return this->stop || !this->tasks.empty(); });
                        if(this->stop && this->tasks.empty())
                            return;
                        task = std::move(this->tasks.front());
                        this->tasks.pop();
                    }

                    task();
                }
                //
                std::unique_lock<std::mutex> lock(this->queue_mutex);
                while (!this->stop) {
                  while (this->tasks.empty() && !this->stop) {
                      this->condition.wait(lock);
                  }
                  if (this->stop) {
                    break;
                  }

                  std::function<void()> task;
                  {
                    task = std::move(this->tasks.front());
                    this->tasks.pop();
                    // Decrement count, indicating thread is no longer available.
                    --available_;
                    lock.unlock();

                    // Run the task.
                    try {
                      task();
                    } catch (const std::exception& e) {
                      LOG(ERROR) << "Exception in thread pool task: " << e.what();
                    } catch (...) {
                      LOG(ERROR) << "Exception in thread pool task: unknown";
                    }
                  }
                  lock.lock();
                  ++available_;
                }
                //
                this->main_loop();
                //
            }
        );
}

void ThreadPool::main_loop() {}

 

 

 

// add new work item to the pool
template<class F, class... Args>
auto ThreadPool::enqueue(F&& f, Args&&... args)
    -> std::future<typename std::result_of<F(Args...)>::type>
{
    using return_type = typename std::result_of<F(Args...)>::type;

    auto task = std::make_shared< std::packaged_task<return_type()> >(
            std::bind(std::forward<F>(f), std::forward<Args>(args)...)
        );

    std::future<return_type> res = task->get_future();
    {
        std::unique_lock<std::mutex> lock(queue_mutex);

        // don't allow enqueueing after stopping the pool
        if(stop)
            throw std::runtime_error("enqueue on stopped ThreadPool");

        tasks.emplace([task](){ (*task)(); });
    }
    condition.notify_one();
    return res;
}

// OK
void ThreadPool::enqueue(std::function<void()> func) {
  if (workers.size() == 0) {
    throw std::runtime_error("No threads to run a task");
  }
  std::unique_lock<std::mutex> lock(queue_mutex);

  // Set task and signal condition variable so that a worker thread will
  // wake up and use the task.
  tasks.emplace(std::move(func));
  condition_.notify_one();
}

// the destructor joins all threads #OK
inline ThreadPool::~ThreadPool()
{
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        stop = true;
    }
    condition.notify_all();
    for(std::thread &worker: workers)
        try {
            worker.join();
        } catch (const std::exception&) {

        }
}

 

size_t ThreadPool::size() const {
  return workers.size();
}

size_t ThreadPool::numAvailable() const {
  std::unique_lock<std::mutex> lock(queue_mutex);
  return available_;
}

bool ThreadPool::inThreadPool() const {
  for (auto& thread : workers) {
    if (thread.get_id() == std::this_thread::get_id()) {
      return true;
    }
  }
  return false;
}
#endif