Linux C : A better way to sleep/timer?

jimmy416 · 10-13-2003, 08:06 PM

currently i am using system("sleep 1"); to cause a delay in my loop

however, a 1 second delay is too long. I need to get down to millisecond delaying...anyone know how?

jstic04@cp.centennialcollege.ca

h/w · 10-13-2003, 08:14 PM

i havent tried it, but manpage for sleep says that the number could be a floating point. can u give a sleep(0.001) for a 1ms delay?

jimmy416 · 10-13-2003, 08:18 PM

h/w : ill give that a try, but strace of sleep 1 showed me that a function called nanosleep() exists, and its in the time.h api.

im readin the man page for nanosleep() now. ill let you know the details when i get back.

h/w · 10-13-2003, 08:18 PM

well, it works at cmd line

Hko · 10-14-2003, 12:44 PM

Quote:

Originally posted by jimmy416
currently i am using system("sleep 1"); to cause a delay in my loop

Better use the sleep() function.
See "man 3 sleep".

Quote:

Originally posted by jimmy416
however, a 1 second delay is too long. I need to get down to millisecond delaying...anyone know how?

Use the usleep() function for microseconds. See "man 3 usleep".

orgcandman · 10-14-2003, 12:53 PM

what's even better than sleep and usleep??
select() of course. Selecting on no file descriptors with NULLs as sets, you can set a timer up to delay as many microseconds as you'd like. In fact, if you man select you'll find that it suggests using that as a nice delay. I don't know of any portability issues with it, but ymmv.

Aaron

Hko · 10-14-2003, 01:15 PM

Quote:

Originally posted by orgcandman
what's even better than sleep and usleep??
select() of course.

When you only need a delay, why use select()?
Select() is really a overly complex way to just usleep().

orgcandman · 10-14-2003, 01:37 PM

yeah, but hasn't usleep been deprecated because it has unspecified interactions with sigalarm and friends? Also, usleep has some portability issues with BSD/SysV/glibc etc... whereas select() doesn't

Also, exposure to select() isn't [edit] a bad thing [/edit] in case that helps him with his project (IE: He was sleeping because some other process was writing to a file that he wanted to read from so he guessed that it was done writing after X seconds, etc...)

Aaron

Hko · 10-14-2003, 01:58 PM

Quote:

Originally posted by orgcandman
yeah, but hasn't usleep been deprecated because it has unspecified interactions with sigalarm and friends? Also, usleep has some portability issues with BSD/SysV/glibc etc... whereas select() doesn't

I didn't know that. And your right. The man page says:
"This function is obsolete. Use nanosleep(2) or setitimer(2) instead."
(note however that it does not recommend select() instead of usleep() )

Quote:

Originally posted by orgcandman
Also, exposure to select() isn't a bad thing in case that helps him with his project

True. One could learn much about programming finding out how select() works, as it is quite complex.

Quote:

Originally posted by orgcandman
(IE: He was sleeping because some other process was writing to a file that he wanted to read from so he guessed that it was done writing after X seconds, etc...)

Well, yes, but that is either just your guess, or you know more about his specific project than what's in this thread.