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#include <iostream>
#include <vector>
#include <thread>
#include <string>
#include <chrono>
#include <random>
#include <condition_variable>
#include <boost/asio.hpp>
 
 
struct worker_pool
{
    boost::asio::io_service _io_service;
    boost::asio::io_service::work _work { _io_service };
 
    std::vector<std::thread> _threads;
 
    std::condition_variable _cv;
    std::mutex _cvm;
    size_t _tasks = 0;
 
 
    void start()
    {
        for (int i = 0 ; i < 8 ; ++i) {
            _threads.emplace_back(std::bind(&worker_pool::thread_proc, this));
        }
    }
 
    void wait()
    {
        std::unique_lock<std::mutex> lock(_cvm);
        _cv.wait(lock, [this] { return _tasks == 0; });
    }
 
    void stop()
    {
        wait();
        _io_service.stop();
        for (auto& t : _threads) {
            if (t.joinable())
                t.join();
        }
        _threads.clear();
 
    }
 
    void thread_proc()
    {
        while (!_io_service.stopped())
        {
            _io_service.run();
        }
    }
 
    void reduce() {
 
        std::unique_lock<std::mutex> lock(_cvm);
        if (--_tasks == 0) {
            lock.unlock();
            _cv.notify_all();
        }
    }
 
    template<class F>
    void submit(F&& f)
    {
        std::unique_lock<std::mutex> lock(_cvm);
        ++ _tasks;
        lock.unlock();
        _io_service.post([this, f = std::forward<F>(f)]
                         {
                             f();
                             reduce();
                         });
 
 
    }
};
 
struct some_other_work
{
    some_other_work(int index, std::chrono::milliseconds delay)
    : _index(index), _delay(delay)
    {}
 
    void operator()() const {
        std::this_thread::sleep_for(_delay);
        printf( "I am worker: %d\n", _index);
    }
 
    int _index;
    std::chrono::milliseconds _delay;
};
 
auto main() -> int
{
    worker_pool pool;
    pool.start();
 
    for (int i = 0 ; i < 100 ; ++i) 
    {
        std::chrono::milliseconds delay(500);
        pool.submit(some_other_work(i, delay));
    }
 
    pool.wait();
    pool.stop();
 
    return 0;
}
 

/home/7Jhm7a/ccGu6O2h.o: In function `boost::asio::detail::task_io_service::shutdown_service()':
prog.cpp:(.text._ZN5boost4asio6detail15task_io_service16shutdown_serviceEv[_ZN5boost4asio6detail15task_io_service16shutdown_serviceEv]+0x6c): undefined reference to `boost::system::system_category()'
/home/7Jhm7a/ccGu6O2h.o: In function `boost::asio::detail::task_io_service::~task_io_service()':
prog.cpp:(.text._ZN5boost4asio6detail15task_io_serviceD2Ev[_ZN5boost4asio6detail15task_io_serviceD5Ev]+0x32): undefined reference to `boost::system::system_category()'
/home/7Jhm7a/ccGu6O2h.o: In function `boost::asio::detail::task_io_service::~task_io_service()':
prog.cpp:(.text._ZN5boost4asio6detail15task_io_serviceD0Ev[_ZN5boost4asio6detail15task_io_serviceD5Ev]+0x32): undefined reference to `boost::system::system_category()'
/home/7Jhm7a/ccGu6O2h.o: In function `boost::asio::detail::task_io_service_thread_info::~task_io_service_thread_info()':
prog.cpp:(.text._ZN5boost4asio6detail27task_io_service_thread_infoD2Ev[_ZN5boost4asio6detail27task_io_service_thread_infoD5Ev]+0x32): undefined reference to `boost::system::system_category()'
/home/7Jhm7a/ccGu6O2h.o: In function `worker_pool::thread_proc()':
prog.cpp:(.text._ZN11worker_pool11thread_procEv[_ZN11worker_pool11thread_procEv]+0x45): undefined reference to `boost::system::system_category()'
/home/7Jhm7a/ccGu6O2h.o:prog.cpp:(.text._ZN11worker_pool11thread_procEv[_ZN11worker_pool11thread_procEv]+0x56): more undefined references to `boost::system::system_category()' follow
/home/7Jhm7a/ccGu6O2h.o: In function `_GLOBAL__sub_I_main':
prog.cpp:(.text.startup+0x695): undefined reference to `boost::system::generic_category()'
prog.cpp:(.text.startup+0x69a): undefined reference to `boost::system::generic_category()'
prog.cpp:(.text.startup+0x69f): undefined reference to `boost::system::system_category()'
prog.cpp:(.text.startup+0x6a4): undefined reference to `boost::system::system_category()'
collect2: error: ld returned 1 exit status

Standard output is empty