How to make thread sleep less than a millisecond on Windows

Jorge Ferreira picture Jorge Ferreira · Sep 17, 2008 · Viewed 80.4k times · Source

On Windows I have a problem I never encountered on Unix. That is how to get a thread to sleep for less than one millisecond. On Unix you typically have a number of choices (sleep, usleep and nanosleep) to fit your needs. On Windows, however, there is only Sleep with millisecond granularity.

On Unix, I can use the use the select system call to create a microsecond sleep which is pretty straightforward:

int usleep(long usec)
{
    struct timeval tv;
    tv.tv_sec = usec/1000000L;
    tv.tv_usec = usec%1000000L;
    return select(0, 0, 0, 0, &tv);
}

How can I achieve the same on Windows?

Answer

Joel Coehoorn picture Joel Coehoorn · Sep 17, 2008

This indicates a mis-understanding of sleep functions. The parameter you pass is a minimum time for sleeping. There's no guarantee that the thread will wake up after exactly the time specified. In fact, threads don't "wake up" at all, but are rather chosen for execution by the OS scheduler. The scheduler might choose to wait much longer than the requested sleep duration to activate a thread, especially if another thread is still active at that moment.