avoiding busy wait with boost::asio poll

Question

I'm writing a service on linux that uses boost::asio::io_service with io_service::poll in a while loop. This is a busy wait loop, e.g. it wastes CPU cycles.

void Application::run()
{
    try
    {
        std::cout << "TcpServer starting..\n";
        _TcpServer.reset( new TcpServer(_io_service, boost::ref(_spState)) );

        // _io_service.run();

        while( ! _spState->QuitSignalled() )
        {
            _io_service.poll(); 
        }

        std::cerr << "quit signalled, TcpServer stopping.. :/" << std::endl;
    }
    catch(std::exception & e)
    {
        std::cout << e.what() << "\n";
    }
}

I use poll instead of run to check if another thread in the service has signalled service shutdown.

Is there a way of achieving this without using poll in a busy wait loop ?

The service uses async io on a single thread, and other threads do data processing.

I've added a sleep between iterations of the loop which seems to reduce the waste of cpu time, but I was hoping there might be a more efficient way?

void Application::run()
{
    using boost::this_thread::sleep_for;

    static const boost::chrono::milliseconds napMsecs( 50 );

    try
    {
        std::cout << "TcpServer starting..\n";
        _TcpServer.reset( new TcpServer(_io_service, boost::ref(_spState)) );

        // _io_service.run();

        while( ! _spState->QuitSignalled() )
        {
            _io_service.poll();
            boost::this_thread::sleep_for( napMsecs );
        }

        std::cerr << "quit signalled, TcpServer stopping.. :/" << std::endl;
    }
    catch(std::exception & e)
    {
        std::cout << e.what() << "\n";
    }
}

sehe sehe · Accepted Answer · 2014-10-09T07:48:31

I'd say, simply take advantage of the fact that boost::asio::io_service is fully threadsafe by default, and do

iosvc.run();

And signal service shutdown on "another thread in the service" like you would:

iosvc.stop();

Remember to iosvc.reset() before you call {run,poll}[_one] again, as per the documentation.

Of course you can also use other means to signal the actual logical workers to end, but then that's completely independent unrelated to Boost Asio

avoiding busy wait with boost::asio poll

1 Answers