martin@macadam.mqcs.mq.oz.au (Martin Foord) (11/06/90)
Is the smallest interval of sleep time the integer 1? Is there anyway of sleeping from a C program for a smaller period of time ? Martin.
gwyn@smoke.brl.mil (Doug Gwyn) (11/06/90)
In article <725@macuni.mqcc.mq.oz> martin@macadam.mqcs.mq.oz.au (Martin Foord) writes: >Is the smallest interval of sleep time the integer 1? Is there anyway of >sleeping from a C program for a smaller period of time ? The first thing you need to be aware of is that all you can specify is a MINIMUM amount of delay; the actual delay will depend on scheduling issues such as system load, and could be arbitrarily large if you're unlucky. There is no standard library function that you can count on in all environments for "napping" (the usual name for short sleeps). The following code is adapted from my System V emulation support for 4BSD and exploits the 4BSD select() system call. On System V you might be able to use poll() in a similar way. /* _nap -- support routine for 4.2BSD system call emulations last edit: 29-Oct-1984 D A Gwyn */ extern int _select(); int _nap( usec ) /* returns 0 if ok, else -1 */ long usec; /* delay in microseconds */ { static struct /* `timeval' */ { long tv_sec; /* seconds */ long tv_usec; /* microsecs */ } delay; /* _select() timeout */ delay.tv_sec = usec / 1000000L; delay.tv_usec = usec % 1000000L; return _select( 0, (long *)0, (long *)0, (long *)0, &delay ); }
lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall) (11/07/90)
In article <14347@smoke.brl.mil> gwyn@smoke.brl.mil (Doug Gwyn) writes: : In article <725@macuni.mqcc.mq.oz> martin@macadam.mqcs.mq.oz.au (Martin Foord) writes: : >Is the smallest interval of sleep time the integer 1? Is there anyway of : >sleeping from a C program for a smaller period of time ? : : The first thing you need to be aware of is that all you can specify is a : MINIMUM amount of delay; the actual delay will depend on scheduling : issues such as system load, and could be arbitrarily large if you're : unlucky. The second thing you need to be aware of is that it doesn't necessarily specify the MINIMUM delay either. If you say sleep(1), some implementations will sleep till the top of the next second, which could be a very small fraction of a second away. So sleep(n) sleeps a minimum of n-1 seconds on such machines. In terms of portability, sleep(1) is virtually worthless (except in a statistical sense) without knowing when in the second it's going to sleep. Machines on which alarm() is implemented using setitimer() do not appear to have this problem. It's possible it's been fixed elsewhere too--some of my databanks haven't been updated in quite some time. I could even be getting confused with other OS's. Caveat Programmor. Larry Wall lwall@jpl-devvax.jpl.nasa.gov
prc@erbe.se (Robert Claeson) (11/08/90)
In a recent article martin@macadam.mqcs.mq.oz.au (Martin Foord) writes: >Is the smallest interval of sleep time the integer 1? Is there anyway of >sleeping from a C program for a smaller period of time ? In general, yes. But Xenix and System V Release 3.2-4.0 has the "nap()" function, which allow sub-second sleeps. Some systems has a "usleep()" function for the same purpose. System V Release 3.0 and 3.1 can be tricked into doing this with the "poll()" system call, and BSD systems can be fooled into doing this using the poll-like "select()" system call. Came to think of it, nap() and usleep() are probably implemented as system calls on most systems. -- Robert Claeson |Reasonable mailers: rclaeson@erbe.se ERBE DATA AB | Dumb mailers: rclaeson%erbe.se@sunet.se Jakobsberg, Sweden | Perverse mailers: rclaeson%erbe.se@encore.com Any opinions expressed herein definitely belongs to me and not to my employer.
root@tndsyd.oz (Berny Goodheart) (11/08/90)
Or: UNIX Curses Explained --- Berny Goodheart -- ISBN 0 13 931957 3 Prentice Hall -- Just published.