C microsecond sleep

ocularbob · 03-31-2004, 08:26 AM

i need a function in my program that works just like sleep() only for microseconds rather than seconds.

mss_sleep(int time)
{
????????
}

i'm sure this problem has been tackled before.
any ideas?
thanks

skel · 03-31-2004, 08:44 AM

usleep()

look at man 3 usleep

aluser · 03-31-2004, 08:51 AM

be careful in that usleep() and nanosleep() may always sleep for at least 1 or 10 milliseconds regardless of how long you ask to sleep. If you need less than this, the nanosleep manpage says some stuff about using sched_setscheduler to make it so you will spin instead of sleep.

skel · 03-31-2004, 08:52 AM

Quote:

Originally posted by aluser
be careful in that usleep() and nanosleep() may always sleep for at least 1 or 10 milliseconds regardless of how long you ask to sleep. If you need less than this, the nanosleep manpage says some stuff about using sched_setscheduler to make it so you will spin instead of sleep.

aluser:
thanks for clearing that up, i didn't know that

ocularbob · 03-31-2004, 10:24 AM

i knew it had to be in a header somewhere.
thanks alot

infamous41md · 03-31-2004, 11:51 AM

what about using select, is that subject to the same 1or10?

skel · 03-31-2004, 12:02 PM

wouldn't you have to do a bit of a workaround to use select as a sleep timer ?

i think you would need a file descriptor that is never ready for i/o and then just let select block until it times out.

but i suspect that select is prone to the same issue with the 1 to 10 millisecond sleep, but i don't know for sure

aluser · 03-31-2004, 02:38 PM

I am 99% sure select will suffer the same problem with regards to accuracy. If the process yields processor time it may sleep for as long as 1/HZ seconds and there's not much to be done about it. The only way to wait for shorter periods is to spin.

HZ is 100 on x86 with 2.4.x and before, and 1000 on x86 with 2.6.x

To use select as a sleep, just select(1, NULL, NULL, NULL, &timeout) -- no need to create any file descriptor.