在1个线程上运行的boost :: asio :: io_service如何唤醒等待状态

Question

Thanks for you reply Sam Miller, but i need to implement it on windows.

Look at this example o wrote:

boost::mutex mut;
boost::condition_variable cond;

boost::asio::io_service io_service;

boost::asio::deadline_timer t(io_service);

void test_func()
{
    boost::mutex::scoped_lock lk(mut);
    cond.notify_all();
}

void cancel_test_func()
{
    boost::unique_lock< boost::mutex > lk(mut);
    auto canceled_timers = t.cancel();
    cond.wait(lk);
    printf("Canceled...%u.", canceled_timers);
}

int main(int argc, char* argv[])
{
  try
  {
    t.expires_from_now(boost::posix_time::seconds(5));
    t.async_wait(boost::bind(&test_func));

    io_service.post(boost::bind(cancel_test_func));

    boost::thread_group tg;
    tg.create_thread( boost::bind(&boost::asio::io_service::run, &io_service) );
    //tg.create_thread( boost::bind(&boost::asio::io_service::run, &io_service) );

    getchar();
  }
  catch (std::exception& e)
  {
    std::cerr << "Exception: " << e.what() << "\n";
  }

  return 0;
}

To make this example works(cancel the timer) i need to uncomment the second thread creation. With only one thread, i never receive notification. The question is: is this behavior normal?

Answer 1

A condition variable is a synchronous concept, it doesn't integrate well with an event loop like an io_service . If you want asynchronous events on Linux, look at eventfd(2) with with EFD_SEMAPHORE flag for semaphore semantics. I'm not sure if there's an analogous interface on other platforms