C++ 线程池 代码举例

代码总共分两部分：ThreadPool.h和example.cpp。这个线程池的实现基于C++11版本以上，可以添加各种类型的线程任务，并且能够获得任务的返回值。下面是一个代码举例：

#include <iostream>
#include <functional>
#include <thread>
#include <vector>
#include <queue>
#include <future>
#include <mutex>
#include <condition_variable>

class ThreadPool {
public:
    ThreadPool(size_t numThreads) : stop(false) {
        for (size_t i = 0; i < numThreads; ++i) {
            workers.emplace_back(
                [this] {
                    for (;;) {
                        std::function<void()> task;
                        {
                            std::unique_lock<std::mutex> lock(this->queueMutex);
                            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();
                    }
                }
            );
        }
    }

    template<typename F, typename... Args>
    auto enqueue(F&& f, Args&&... args) -> std::future<typename std::result_of<F(Args...)>::type> {
        using returnType = typename std::result_of<F(Args...)>::type;
        auto task = std::make_shared<std::packaged_task<returnType()>>(
            std::bind(std::forward<F>(f), std::forward<Args>(args)...)
        );
        std::future<returnType> result = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            if (stop) {
                throw std::runtime_error("enqueue on stopped ThreadPool");
            }
            tasks.emplace([task]() { (*task)(); });
        }
        condition.notify_one();
        return result;
    }

    ~ThreadPool() {
        {
            std::unique_lock<std::mutex> lock(queueMutex);
            stop = true;
        }
        condition.notify_all();
        for (std::thread& worker : workers) {
            worker.join();
        }
    }

private:
    std::vector<std::thread> workers;
    std::queue<std::function<void()>> tasks;
    std::mutex queueMutex;
    std::condition_variable condition;
    bool stop;
};

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::this_thread::sleep_for(std::chrono::seconds(1));
                return i * i;
            })
        );
    }

    for (auto&& result : results) {
        std::cout << result.get() << ' ';
    }
    std::cout << std::endl;

    return 0;
}

此代码使用了C++11的多线程功能，通过使用std::packaged_task和std::future获取任务的返回值，并使用std::function封装任务。线程池的大小可以通过构造函数参数进行指定。在主函数中，我们向线程池中添加了8个任务，并通过std::future获取了每个任务的返回值，并输出到控制台。