c++11线程池的实现原理及回调函数的使用

#include <iostream>
#include <chrono>
#include <thread>
#include <future>
#include "threadpool.h"
using namespace std;
using namespace std::chrono;

//仿函数示例
struct gfun {
	int operator()(int n) {
		printf("%d  hello, gfun !  %d\n" ,n, std::this_thread::get_id() );
		return 42;
	}
};

class A { 
	public:
		static std::string Bfun(int n, std::string str, char c) {
			std::cout << n << "  hello, Bfun !  "<< str.c_str() <<"  " << (int)c <<"  " << std::this_thread::get_id() << std::endl;
			return str;
		}
};


int main() {

	cout << "hello,this is a test using threadpool" <<endl;

	me::ThreadPool pool(4);
	std::vector< std::future<int> > results;

	//lambada表达式 匿名函数线程中执行
	pool.commit([] {
			std::cout << "this is running in pool therad " << std::endl;
			std::this_thread::sleep_for(std::chrono::seconds(1));
			});

	//仿函数放到线程池中执行
	std::future<int> fg = pool.commit(gfun{},0);	

	std::future<std::string> gh = pool.commit(A::Bfun, 999,"mult args", 123);
	//回调函数示例,模拟耗时操作,结果回调输出
	auto fetchDataFromDB = [](std::string recvdData,std::function<int(std::string &)> cback) {
		// Make sure that function takes 5 seconds to complete
		std::this_thread::sleep_for(seconds(5));
		//Do stuff like creating DB Connection and fetching Data
		if(cback != nullptr){
			std::string out = "this is from callback ";
			cback(out);
		}
		return "DB_" + recvdData;
	};

	//模拟，回调
	fetchDataFromDB("aaa",[&](std::string &result){
			std::cout << "callback result:" << result << std::endl;
			return 0;
			} );

	//把fetchDataFromDB这一IO耗时任务放到线程里异步执行
	//
	std::future<std::string> resultFromDB = std::async(std::launch::async, fetchDataFromDB, "Data0",
			[&](std::string &result){
			std::cout << "callback result from thread:" << result << std::endl;
			return 0;
			});	


	//把fetchDataFromDB这一IO耗时操作放到pool中的效果
	pool.commit(fetchDataFromDB,"Data1",[&](std::string &result){
			std::cout << "callback result from pool thread:" << result << std::endl;
			return 0;
			});


	for(int i = 0; i < 8; ++i) {
		results.emplace_back(
				pool.commit([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;
}

#pragma once
#ifndef THREAD_POOL_H
#define THREAD_POOL_H

#include <vector>
#include <queue>
#include <atomic>
#include <future>
//#include <condition_variable>
//#include <thread>
#include <functional>
#include <stdexcept>

namespace me
{
  using namespace std;
//线程池最大容量,应尽量设小一点
#define  THREADPOOL_MAX_NUM 16
//#define  THREADPOOL_AUTO_GROW

//线程池,可以提交变参函数或拉姆达表达式的匿名函数执行,可以获取执行返回值
//不直接支持类成员函数, 支持类静态成员函数或全局函数,Opteron()函数等
class ThreadPool
{
    using Task = function<void()>;    //定义类型
    vector<thread> _pool;     //线程池
    queue<Task> _tasks;            //任务队列
    mutex _lock;                   //同步
    condition_variable _task_cv;   //条件阻塞
    atomic<bool> _run{ true };     //线程池是否执行
    atomic<int>  _idlThrNum{ 0 };  //空闲线程数量

public:
    inline ThreadPool(unsigned short size = 4) { addThread(size); }
    inline ~ThreadPool()
    {
        _run=false;
        _task_cv.notify_all(); // 唤醒所有线程执行
        for (thread& thread : _pool) {
            //thread.detach(); // 让线程“自生自灭”
            if(thread.joinable())
                thread.join(); // 等待任务结束， 前提：线程一定会执行完
        }
    }

public:
    // 提交一个任务
    // 调用.get()获取返回值会等待任务执行完,获取返回值
    // 有两种方法可以实现调用类成员，
    // 一种是使用   bind： .commit(std::bind(&Dog::sayHello, &dog));
    // 一种是用   mem_fn： .commit(std::mem_fn(&Dog::sayHello), this)
    template<class F, class... Args>
    auto commit(F&& f, Args&&... args) ->future<decltype(f(args...))>
    {
        if (!_run)    // stoped ??
            throw runtime_error("commit on ThreadPool is stopped.");

        using RetType = decltype(f(args...)); // typename std::result_of<F(Args...)>::type, 函数 f 的返回值类型
        auto task = make_shared<packaged_task<RetType()>>(
            bind(forward<F>(f), forward<Args>(args)...)
        ); // 把函数入口及参数,打包(绑定)
        future<RetType> future = task->get_future();
        {    // 添加任务到队列
            lock_guard<mutex> lock{ _lock };//对当前块的语句加锁  lock_guard 是 mutex 的 stack 封装类，构造的时候 lock()，析构的时候 unlock()
            _tasks.emplace([task](){ // push(Task{...}) 放到队列后面
                (*task)();
            });
        }
#ifdef THREADPOOL_AUTO_GROW
        if (_idlThrNum < 1 && _pool.size() < THREADPOOL_MAX_NUM)
            addThread(1);
#endif // !THREADPOOL_AUTO_GROW
        _task_cv.notify_one(); // 唤醒一个线程执行

        return future;
    }

    //空闲线程数量
    int idlCount() { return _idlThrNum; }
    //线程数量
    int thrCount() { return _pool.size(); }
#ifndef THREADPOOL_AUTO_GROW
private:
#endif // !THREADPOOL_AUTO_GROW
    //添加指定数量的线程
    void addThread(unsigned short size)
    {
        for (; _pool.size() < THREADPOOL_MAX_NUM && size > 0; --size)
        {   //增加线程数量,但不超过 预定义数量 THREADPOOL_MAX_NUM
            _pool.emplace_back( [this]{ //工作线程函数
                while (_run)
                {
                    Task task; // 获取一个待执行的 task
                    {
                        // unique_lock 相比 lock_guard 的好处是：可以随时 unlock() 和 lock()
                        unique_lock<mutex> lock{ _lock };
                        _task_cv.wait(lock, [this]{
                                return !_run || !_tasks.empty();
                        }); // wait 直到有 task
                        if (!_run && _tasks.empty())
                            return;
                        task = move(_tasks.front()); // 按先进先出从队列取一个 task
                        _tasks.pop();
                    }
                    _idlThrNum--;
                    task();//执行任务
                    _idlThrNum++;
                }
            });
            _idlThrNum++;
        }
    }
};

}

#endif  //https://github.com/lzpong/