thread_pool.hpp

// By Emil Ernerfeldt 2016
// LICENSE:
//   This software is dual-licensed to the public domain and under the following
//   license: you are granted a perpetual, irrevocable license to copy, modify,
//   publish, and distribute this file as you see fit.

#pragma once

#include <condition_variable>
#include <deque>
#include <functional>
#include <future>
#include <memory>
#include <mutex>
#include <thread>
#include <vector>

namespace emilib {

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

    ThreadPool();

    explicit ThreadPool(size_t num_threads);

    ~ThreadPool();

    void wait();

    void clear();

    void add_void(const Job& job);

    template<typename Result>
    std::future<Result> add(std::function<Result()> job)
    {
        const auto promise = std::make_shared<std::promise<Result>>();
        std::future<Result> future = promise->get_future();
        add_void([=]() {
            promise->set_value(job());
        });
        return future;
    }

    // TODO: add way to add jobs to front of queue.
    // TODO: add way to add job after waiting for for empty queue first.

private:
    void _thread_worker(size_t thread_nr);

    std::mutex               _mutex;
    std::vector<std::thread> _threads;
    std::deque<Job>          _job_queue;
    size_t                   _num_unfinished_jobs = 0;
    std::condition_variable  _new_job_cond;
    std::condition_variable  _job_finished_cond;
};

} // namespace emilib