Question

Is it possible to perform an asynchronous wait (read : non-blocking) on a conditional variable in boost::asio ? if it isn’t directly supported any hints on implementing it would be appreciated.

I could implement a timer and fire a wakeup even every few ms, but this is approach is vastly inferior, I find it hard to believe that condition variable synchronization is not implemented / documented.

Answer 1

If I understand the intent correctly, you want to launch an event handler, when some condition variable is signaled, in context of asio thread pool? I think it would be sufficient to wait on the condition variable in the beginning of the handler, and io_service::post() itself back in the pool in the end, something of this sort:

#include <iostream>
#include <boost/asio.hpp>
#include <boost/thread.hpp>
boost::asio::io_service io;
boost::mutex mx;
boost::condition_variable cv;
void handler()
{
    boost::unique_lock<boost::mutex> lk(mx);
         cv.wait(lk);
    std::cout << "handler awakened\n";
    io.post(handler);
}
void buzzer()
{
    for(;;)
    {
        boost::this_thread::sleep(boost::posix_time::seconds(1));
        boost::lock_guard<boost::mutex> lk(mx);
            cv.notify_all();
    }
}
int main()
{
    io.post(handler);
    boost::thread bt(buzzer);
    io.run();
}