c++实现线程池

线程池技术是为了避免频繁的创建和销毁线程所带来的开销。
线程池是一个典型的生产者-消费者模型，用户将要执行的任务添加到任务队列，并通知线程池，线程池则唤醒其中的一个线程来处理任务。一个简单的c++线程池实现如下所示：

#include <iostream>
#include <vector>
#include <deque>
#include <thread>
#include <mutex>
#include <condition_variable>
#include <functional>
#include <atomic>
#include <unistd.h>

using namespace std;

class ThreadPool
{
public:
    using TaskEntry = function<void ()>;

    ThreadPool(int size)
    {
        running.store(false);
        stopflag.store(false);
        int enablecpunums = sysconf(_SC_NPROCESSORS_ONLN);
        threadpoolsize = (size > 0 && size < enablecpunums) ? size : enablecpunums;
    }

    ~ThreadPool()
    {
        if (running.load()) { stop(); }
    }

    void start()
    {
        running.store(true);
        threadbuckets.reserve(threadpoolsize);
        for (int i = 0; i < threadpoolsize; i++)
        {
            threadbuckets.emplace_back(new thread(bind(&ThreadPool::TaskInitEntry, this)));
        }
    }

    void stop()
    {
        stopflag.store(true);
        while (1)
        {
            threadpoolmutex.lock();
            int n = taskbuckets.size();
            threadpoolmutex.unlock();
            if (0 == n) break;
            usleep(500*1000);
        }
        running.store(false);
        threadpoolconvar.notify_all();
        for (int i = 0; i < threadpoolsize; i++)
        {
            threadbuckets[i]->join();
        }
    }

    void run(TaskEntry task)
    {
        if (stopflag.load() || !running.load() || !task) return;
        unique_lock<mutex> lock(threadpoolmutex);
        taskbuckets.push_back(task);
        threadpoolconvar.notify_one();
    }

private:
    void TaskInitEntry()
    {
        while (running.load())
        {
            unique_lock<mutex> lock(threadpoolmutex);
            threadpoolconvar.wait(lock, [this]{ return !running.load() || !taskbuckets.empty(); });
            if (!running.load() && taskbuckets.empty()) return;
            TaskEntry task = taskbuckets.front();
            taskbuckets.pop_front();
            task();
        } 
    }

private:
    atomic<bool> running;
    atomic<bool> stopflag;
    mutex threadpoolmutex;
    int threadpoolsize;
    condition_variable threadpoolconvar;
    vector<unique_ptr<thread>> threadbuckets;
    deque<TaskEntry> taskbuckets;
};


int main()
{
    ThreadPool threadpool(8);
    threadpool.start();
    for (int i = 0; i < 100; i++)
    {
        threadpool.run([]{ cout << "abcdefg\n"; });
    }
    threadpool.stop();
    return 0;
}

参考资料：

1. muduo ThreadPool源码
2. https://github.com/progschj/ThreadPool/blob/master/ThreadPool.h