线程池的C++11简单实现，源代码来自Github上作者progschj，地址为：A simple C++11 Thread Pool implementation，具体博客可以参见Jakob’s Devlog，地址为：A Thread Pool with C++11
1、线程池的实现代码如下：
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
2、基本的用法：
// create thread pool with 4 worker threads
ThreadPool pool(4);
// enqueue and store future
auto result = pool.enqueue([](int answer) { return answer; }, 42);
// get result from future
std::cout << result.get() << std::endl;
3、测试C++11线程池的例子程序如下：
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;
}
编译运行example.cpp时需要添加C++11的支持，并且要加入pthread库的链接。
在Linux下的编译的命令为: g++ example.cpp -o example -std=c++11 -lpthread；如果在VS2017中使用，由于默认支持C++11，可以直接创建一个控制台程序，添加ThreadPool.h和example.cpp到项目，编译运行即可。
在Ubuntu18.10下测试如下：
havealex@havealex:~/GithubProjects/ThreadPool$ ls
COPYING example.cpp README.md ThreadPool.h
havealex@havealex:~/GithubProjects/ThreadPool$ g++ example.cpp -o example -std=c++11
/usr/bin/ld: /tmp/ccduRGse.o: in function `std::thread::thread<ThreadPool::ThreadPool(unsigned long)::{lambda()#1}, , void>(ThreadPool::ThreadPool(unsigned long)::{lambda()#1}&&)':
example.cpp:(.text._ZNSt6threadC2IZN10ThreadPoolC4EmEUlvE_JEvEEOT_DpOT0_[_ZNSt6threadC5IZN10ThreadPoolC4EmEUlvE_JEvEEOT_DpOT0_]+0x2f): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
havealex@havealex:~/GithubProjects/ThreadPool$ g++ example.cpp -o example -std=c++11 -lpthread
havealex@havealex:~/GithubProjects/ThreadPool$ ls\
> ^C
havealex@havealex:~/GithubProjects/ThreadPool$ ls
COPYING example example.cpp README.md ThreadPool.h
havealex@havealex:~/GithubProjects/ThreadPool$ ./example
hello 0
hello 1
hello 2
hello 3
world 1
hello 4
world 0
hello 5
0 1 world 2
hello 6
4 world 3
hello 7
9 world 5
world 4
16 25 world 6
36 world 7
49
可以看出，结果的输出是无序并行的。