Thread: Use nanosleep() for pg_usleep() on Unix/Linux?
I happened to read the pg_usleep() code recently. I'm wondering
if we could implement it using the posix function nanosleep(),
instead of by select().
nanosleep() is designed with higher time resolution, besides it provide
remaining time if is interrupted by signal so that pg_usleep() could
be implemented more accurately.
The code for pg_usleep() could be similar like this:
while(nanosleep(&req,&req)==-1 && errno == EINTR)
continue;
or combine with clock_gettime() to control the sleep time more accurately.
Regards,
Paul
Paul Guo <paulguo@gmail.com> writes:
> I happened to read the pg_usleep() code recently. I'm wondering
> if we could implement it using the posix function nanosleep(),
> instead of by select().
That actually looks like a pretty good idea. Some research says that
nanosleep() is defined in SUSv2, our usual baseline for Unix features;
and it appears to be implemented and work per spec on even my oldest
buildfarm critters. So portability looks like a non problem.
It would be nice to have two versions of pg_usleep, one where handling
of a signal was guaranteed to terminate the wait and one where it was
guaranteed not to, rather than the current no-promises situation.
It looks like we could have that on the Unix side using nanosleep(),
but it's not clear to me whether we can do the second case on Windows.
> nanosleep() is designed with higher time resolution, besides it provide
> remaining time if is interrupted by signal so that pg_usleep() could
> be implemented more accurately.
> or combine with clock_gettime() to control the sleep time more accurately.
I do not think we really care about sub-microsecond sleep resolution.
But it would be good if we could implement a sleep that would be
approximately the requested length even with signals received meanwhile.
regards, tom lane