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¿Cómo crear un grupo de subprocesos usando boost en C++?

Question

¿Cómo creo un grupo de subprocesos usando boost en C ++ y cómo asigno tareas al threadpool?

Answer 1

El proceso es bastante simple. Primero crea un asio :: io_service y un thread_group. Rellene thread_group con hilos vinculados al io_service. Asigna tareas a los hilos utilizando la función boost::bind .

Para detener los hilos (generalmente cuando sale de su programa) solo detenga el io_service y únase a todos los hilos.

Solo deberías necesitar estos encabezados:

#include <boost/asio/io_service.hpp>
#include <boost/bind.hpp>
#include <boost/thread/thread.hpp>

Aquí hay un ejemplo:

/*
 * Create an asio::io_service and a thread_group (through pool in essence)
 */
boost::asio::io_service ioService;
boost::thread_group threadpool;


/*
 * This will start the ioService processing loop. All tasks 
 * assigned with ioService.post() will start executing. 
 */
boost::asio::io_service::work work(ioService);

/*
 * This will add 2 threads to the thread pool. (You could just put it in a for loop)
 */
threadpool.create_thread(
    boost::bind(&boost::asio::io_service::run, &ioService)
);
threadpool.create_thread(
    boost::bind(&boost::asio::io_service::run, &ioService)
);

/*
 * This will assign tasks to the thread pool. 
 * More about boost::bind: "http://www.boost.org/doc/libs/1_54_0/libs/bind/bind.html#with_functions"
 */
ioService.post(boost::bind(myTask, "Hello World!"));
ioService.post(boost::bind(clearCache, "./cache"));
ioService.post(boost::bind(getSocialUpdates, "twitter,gmail,facebook,tumblr,reddit"));

/*
 * This will stop the ioService processing loop. Any tasks
 * you add behind this point will not execute.
*/
ioService.stop();

/*
 * Will wait till all the threads in the thread pool are finished with 
 * their assigned tasks and ''join'' them. Just assume the threads inside
 * the threadpool will be destroyed by this method.
 */
threadpool.join_all();

Fuente: Recetas <Asio

Answer 2

Sé que te gusta el código.

Mi version

namespace bamthread
{
    typedef std::unique_ptr<boost::asio::io_service::work> asio_worker;

    struct ThreadPool {
        ThreadPool(size_t threads) :service(), working(new asio_worker::element_type(service)) {
            while(threads--)
            {
                auto worker = boost::bind(&boost::asio::io_service::run, &(this->service));
                g.add_thread(new boost::thread(worker));
            }
        }

        template<class F>
            void enqueue(F f){
                service.post(f);
            }

        ~ThreadPool() {
            working.reset(); //allow run() to exit
            g.join_all();
            service.stop();
        }

        private:
        boost::asio::io_service service; //< the io_service we are wrapping
        asio_worker working;
        boost::thread_group g; //< need to keep track of threads so we can join them
    };
}

Pedazo de código para usarlo:

{
    bamthread::ThreadPool tp(n_threads);
    BOOST_FOREACH(int y, boost::irange(starty, endy, step)){
        int im_x = 0;
        BOOST_FOREACH(int x, boost::irange(startx, endx, step)){
            tp.enqueue (boost::bind(&camera_view_depth::threaded_intersection, this,
                        intersections, 
                        intersected,
                        im_x,
                        im_y,
                        _faces, x, y));
            ++im_x;
        }
        ++im_y;
    }
}