How to add a Manager

[Zzzzzya]

in this demo ,the num of threads in the pool is fixed when the pool is created. Is there a more flexible algorithm or strategy ? How can i add a manager. I mean , in real project ,what should i add to the threadpool? Sorry that my English may be not very good. /(ㄒoㄒ)/~~

[xiays146]

maybe you can fix the following Start func to your own: `

ifndef THREAD_POOL_H

define THREAD_POOL_H

include

include

include

include

include

include

include

include

include

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(); ThreadPool(const ThreadPool &) = delete; ThreadPool(ThreadPool &&) = delete; ThreadPool &operator=(const ThreadPool &) = delete; ThreadPool &operator=(ThreadPool &&) = delete; void Stop() { if (stop) return; { std::unique_lock lock(queue_mutex); stop = true; } condition.notify_all(); for (std::thread &worker : workers) { if (worker.joinable()) worker.join(); } }

void Start(size_t threads)
{
    if (!stop)
        return;
    {
        std::unique_lock<std::mutex> lock(queue_mutex);
        stop = false;
    }
    // TODO: clear workers
    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();
            }
        });
    }
}

private: // need to keep track of threads so we can join them std::vector 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(true) { Start(threads); }

// 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() { Stop(); }

endif

`