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GitHub地址：https://github.com/progschj/ThreadPool
生肉代码
- 线程池实现 ThreadPool.h
#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>;
~ThreadPool();
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;
};
// 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]
{
for(;;)
{
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();
}
}
);
}
// 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;
}
// the destructor joins all threads
inline ThreadPool::~ThreadPool()
{
{
std::unique_lock<std::mutex> lock(queue_mutex);
stop = true;
}
condition.notify_all();
for(std::thread &worker: workers)
worker.join();
}
#endif
- 使用示例 example.cpp
#include <iostream>
#include <vector>
#include <chrono>
#include "ThreadPool.h"
int main()
{
ThreadPool pool(4);
std::vector< std::future<int> > results;
for(int i = 0; i < 8; ++i) {
results.emplace_back(
pool.enqueue([i] {
std::cout << "hello " << i << std::endl;
std::this_thread::sleep_for(std::chrono::seconds(1));
std::cout << "world " << i << std::endl;
return i*i;
})
);
}
for(auto && result: results)
std::cout << result.get() << ' ';
std::cout << std::endl;
return 0;
}
熟肉代码
参考链接：https://blog.csdn.net/gcola007/article/details/78750220
- 线程池实现 ThreadPool.h
#ifndef ThreadPool_h
#define ThreadPool_h
#include <vector>
#include <queue>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <future>
#include <functional>
class ThreadPool {
public:
ThreadPool(size_t); //构造函数，size_t n 表示连接数
template<class F, class... Args>
auto enqueue(F&& f, Args&&... args) //任务管道函数
-> std::future<typename std::result_of<F(Args...)>::type>; //利用尾置限定符 std future用来获取异步任务的结果
~ThreadPool();
private:
// need to keep track of threads so we can join them
std::vector< std::thread > workers; //追踪线程
// the task queue
std::queue< std::function<void()> > tasks; //任务队列，用于存放没有处理的任务。提供缓冲机制
// synchronization 同步？
std::mutex queue_mutex; //互斥锁
std::condition_variable condition; //条件变量？
bool stop;
};
// 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( //以下为构造一个任务，即构造一个线程
[this]
{
for(;;)
{
std::function<void()> task; //线程中的函数对象
{//大括号作用：临时变量的生存期，即控制lock的时间
std::unique_lock<std::mutex> lock(this->queue_mutex);
this->condition.wait(lock,
[this]{ return this->stop || !this->tasks.empty(); }); //当stop==false&&tasks.empty(),该线程被阻塞 !this->stop&&this->tasks.empty()
if(this->stop && this->tasks.empty())
return;
task = std::move(this->tasks.front());
this->tasks.pop();
}
task(); //调用函数，运行函数
}
}
);
}
// add new work item to the pool
template<class F, class... Args>
auto ThreadPool::enqueue(F&& f, Args&&... args) //&& 引用限定符，参数的右值引用， 此处表示参数传入一个函数
-> std::future<typename std::result_of<F(Args...)>::type>
{
using return_type = typename std::result_of<F(Args...)>::type;
//packaged_task是对任务的一个抽象，我们可以给其传递一个函数来完成其构造。之后将任务投递给任何线程去完成，通过
//packaged_task.get_future()方法获取的future来获取任务完成后的产出值
auto task = std::make_shared<std::packaged_task<return_type()> >( //指向F函数的智能指针
std::bind(std::forward<F>(f), std::forward<Args>(args)...) //传递函数进行构造
);
//future为期望，get_future获取任务完成后的产出值
std::future<return_type> res = task->get_future(); //获取future对象，如果task的状态不为ready，会阻塞当前调用者
{
std::unique_lock<std::mutex> lock(queue_mutex); //保持互斥性，避免多个线程同时运行一个任务
// don't allow enqueueing after stopping the pool
if(stop)
throw std::runtime_error("enqueue on stopped ThreadPool");
tasks.emplace([task](){ (*task)(); }); //将task投递给线程去完成，vector尾部压入
}
condition.notify_one(); //选择一个wait状态的线程进行唤醒，并使他获得对象上的锁来完成任务(即其他线程无法访问对象)
return res;
}//notify_one不能保证获得锁的线程真正需要锁，并且因此可能产生死锁
// the destructor joins all threads
inline ThreadPool::~ThreadPool()
{
{
std::unique_lock<std::mutex> lock(queue_mutex);
stop = true;
}
condition.notify_all(); //通知所有wait状态的线程竞争对象的控制权，唤醒所有线程执行
for(std::thread &worker: workers)
worker.join(); //因为线程都开始竞争了，所以一定会执行完，join可等待线程执行完
}
#endif /* ThreadPool_h */
