USLEEP(P)						     POSIX Programmer's Manual							 USLEEP(P)

NAME

       usleep - suspend execution for an interval

SYNOPSIS

       #include <unistd.h>

       int usleep(useconds_t useconds);

DESCRIPTION

       The usleep() function shall cause the calling thread to be suspended from execution until either the number of realtime microseconds speci-
       fied by the argument useconds has elapsed or a signal is delivered to the calling thread and its action	is  to	invoke	a  signal-catching
       function or to terminate the process.  The suspension time may be longer than requested due to the scheduling of other activity by the sys-
       tem.

       The useconds argument shall be less than one million. If the value of useconds is 0, then the call has no effect.

       If a SIGALRM signal is generated for the calling process during execution of usleep() and if the SIGALRM signal is being ignored or blocked
       from  delivery, it is unspecified whether usleep() returns when the SIGALRM signal is scheduled. If the signal is being blocked, it is also
       unspecified whether it remains pending after usleep() returns or it is discarded.

       If a SIGALRM signal is generated for the calling process during execution of usleep(), except as a result of a prior call to  alarm(),  and
       if  the SIGALRM signal is not being ignored or blocked from delivery, it is unspecified whether that signal has any effect other than caus-
       ing usleep() to return.

       If a signal-catching function interrupts usleep() and examines or changes either the time a SIGALRM  is	scheduled  to  be  generated,  the
       action associated with the SIGALRM signal, or whether the SIGALRM signal is blocked from delivery, the results are unspecified.

       If a signal-catching function interrupts usleep() and calls siglongjmp() or longjmp() to restore an environment saved prior to the usleep()
       call, the action associated with the SIGALRM signal and the time at which a SIGALRM signal is scheduled to be generated are unspecified. It
       is also unspecified whether the SIGALRM signal is blocked, unless the process' signal mask is restored as part of the environment.

       Implementations	may place limitations on the granularity of timer values. For each interval timer, if the requested timer value requires a
       finer granularity than the implementation supports, the actual timer value shall be rounded up to the next supported value.

       Interactions between usleep() and any of the following are unspecified:

	      nanosleep()
	      setitimer()
	      timer_create()
	      timer_delete()
	      timer_getoverrun()
	      timer_gettime()
	      timer_settime()
	      ualarm()
	      sleep()

RETURN VALUE

       Upon successful completion, usleep() shall return 0; otherwise, it shall return -1 and set errno to indicate the error.

ERRORS

       The usleep() function may fail if:

       EINVAL The time interval specified one million or more microseconds.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications are recommended to use nanosleep() if  the	Timers	option	is  supported,	or  setitimer(),  timer_create(),  timer_delete(),
       timer_getoverrun(), timer_gettime(), or timer_settime() instead of this function.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       alarm()	,  getitimer() , nanosleep() , sigaction() , sleep() , timer_create() , timer_delete() , timer_getoverrun() , the Base Definitions
       volume of IEEE Std 1003.1-2001, <unistd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								 USLEEP(P)