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usleep(3) [bsd man page]

USLEEP(3)						     Library Functions Manual							 USLEEP(3)

usleep - suspend execution for interval SYNOPSIS
usleep(useconds) unsigned useconds; DESCRIPTION
The current process is suspended from execution for the number of microseconds specified by the argument. The actual suspension time may be an arbitrary amount longer because of other activity in the system or because of the time spent in processing the call. The routine is implemented by setting an interval timer and pausing until it occurs. The previous state of this timer is saved and restored. If the sleep time exceeds the time to the expiration of the previous timer, the process sleeps only until the signal would have occurred, and the signal is sent a short time later. This routine is implemented using setitimer(2); it requires eight system calls each time it is invoked. A similar but less compatible function can be obtained with a single select(2); it would not restart after signals, but would not interfere with other uses of setitimer. SEE ALSO
setitimer(2), getitimer(2), sigpause(2), ualarm(3), sleep(3), alarm(3) NOTES (PDP-11) On the PDP-11, setitimer(2) rounds the number of microseconds up to seconds resolution, therefore usleep doesn't give you any more resolu- tion than sleep(3). Select(2) offers clock resolution (usually 60Hz in the U.S.A. and 50Hz elsewhere) and so should be used instead. 4.3 Berkeley Distribution August 26, 1988 USLEEP(3)

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USLEEP(3)						     Linux Programmer's Manual							 USLEEP(3)

usleep - suspend execution for microsecond intervals SYNOPSIS
#include <unistd.h> void usleep(unsigned long usec); int usleep(unsigned long usec); /* SUSv2 */ DESCRIPTION
The usleep() function suspends execution of the calling process for usec microseconds. The sleep may be lengthened slightly by any system activity or by the time spent processing the call. RETURN VALUE
None (BSD). Or: 0 on success, -1 on error (SUSv2). ERRORS
EINTR Interrupted by a signal. EINVAL usec is not smaller than 1000000. (On systems where that is considered an error.) CONFORMING TO
BSD 4.3. The SUSv2 version returns int, and this is also the prototype used by glibc 2.2.2. Only the EINVAL error return is documented by SUSv2. NOTES
The interaction of this function with SIGALRM and other timer functions such as sleep(), alarm(), setitimer(), nanosleep() is unspecified. This function is obsolete. Use nanosleep(2) or setitimer(2) instead. SEE ALSO
alarm(2), getitimer(2), nanosleep(2), select(2), setitimer(2), sleep(3) 2001-04-02 USLEEP(3)
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