boost asio 类似信号量的解决方案

Question

这个问题是 的后续问题这个问题。无论如何，这就是动机 - 来自原始问题评论的一点 c/p：

我希望能够在多个线程（CalcFib 函数）上发布一组作业，然后当作业结束了，另一组作业（CalcFib2 函数）也位于多个线程上。这个循环循环很多次（这里是两次），所以我认为最好的办法是创建boost::asio::io_service并在循环开始时创建线程，所以我不' t 必须创建&每次循环开始/结束时销毁线程。

我创建了两个 int 变量，错误地命名为 semaphore_**，并在上述函数中递减它们。等待作业组完成的代码是简单的 while ，如下所示。该解决方案有效，至少在我看来是这样。

使用 while 进行等待真的是一种可行的方法吗？我缺少什么？有更好的方法吗？

我的代码如下所示：

#include <boost/asio.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/thread.hpp>
#include <boost/thread/mutex.hpp>
#include <boost/bind.hpp>
#include <iostream>

boost::mutex global_stream_lock;
int semaphore_fib = 0;
int semaphore_fib2 = 0;

void WorkerThread( boost::shared_ptr< boost::asio::io_service > io_service)
{
    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Thread Start" << std::endl;
    global_stream_lock.unlock();

    io_service->run();

    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Thread Finish" << std::endl;
    global_stream_lock.unlock();
}

size_t fib( size_t n )
{
    if ( n <= 1 )
    {
        return n;
    }
    boost::this_thread::sleep( boost::posix_time::milliseconds( 1000 ) );
    return fib( n - 1 ) + fib( n - 2);
}

void CalcFib( size_t n )
{
    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] Now calculating fib( " << n << " ) " << std::endl;
    global_stream_lock.unlock();

    size_t f = fib( n );

    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] fib( " << n << " ) = " << f << std::endl;
    semaphore_fib = semaphore_fib-1;
    global_stream_lock.unlock();
}

void CalcFib2( size_t n )
{
    global_stream_lock.lock();
    std::cout << "\t\t[" << boost::this_thread::get_id()
        << "] Now calculating fib2( " << n << " ) " << std::endl;
    global_stream_lock.unlock();

    size_t f = fib( n );

    global_stream_lock.lock();
    std::cout << "\t\t[" << boost::this_thread::get_id()
        << "] fib2( " << n << " ) = " << f << std::endl;
    semaphore_fib2=semaphore_fib2-1;
    global_stream_lock.unlock();
}

int main( int argc, char * argv[] )
{
    boost::shared_ptr< boost::asio::io_service > io_service(
        new boost::asio::io_service
        );
    boost::shared_ptr< boost::asio::io_service::work > work(
        new boost::asio::io_service::work( *io_service )
        );
    boost::asio::io_service::strand strand( *io_service );

    global_stream_lock.lock();
    std::cout << "[" << boost::this_thread::get_id()
        << "] The program will exit when all work has finished."
        << std::endl;
    global_stream_lock.unlock();

    boost::thread_group worker_threads;
    for( int x = 0; x < 2; ++x )
    {
        worker_threads.create_thread( 
            boost::bind( &WorkerThread, io_service)
            );
    }
    for(int loop_no=0; loop_no<2; ++loop_no)
    {
        semaphore_fib=3;
        io_service->post( boost::bind( CalcFib, 5 ) );
        io_service->post( boost::bind( CalcFib, 4 ) );
        io_service->post( boost::bind( CalcFib, 3 ) );
        while(semaphore_fib>0)
        {
            // waiting
        }

        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] ******* CalcFib group finished ********" << std::endl;
        global_stream_lock.unlock();

        semaphore_fib2=3;
        io_service->post( boost::bind( CalcFib2, 2 ) );
        io_service->post( boost::bind( CalcFib2, 1 ) );
        io_service->post( boost::bind( CalcFib2, 1 ) );
        while(semaphore_fib2>0)
        {
            // waiting
        }
        global_stream_lock.lock();
        std::cout << "[" << boost::this_thread::get_id()
            << "] ******* CalcFib2 group finished  ********" << std::endl;
        global_stream_lock.unlock();
    }
    work.reset();
    worker_threads.join_all();

    return 0;
} 

Answer 1

这就是我解决 main() 中 while 循环中过多 if 语句的方法。

• 添加了 boost::condition_variable cv; 和 boost::mutex mx; 作为全局变量
• 添加了 boost::lock_guard; lk(mx);cv.notify_all();
  在 CalcFib 和 CalcFib2 函数末尾
• 添加了 boost::unique_locklk(mx); cv.wait(lk);
  在每个 while 循环中

这样我就完成了 while 循环中的 if 语句仅在 cv.notify_all()< 时执行/code> 执行。