USLEEP(P) POSIX Programmer's Manual USLEEP(P)NAMEusleep - 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 func‐
tion or to terminate the process. The suspension time may be longer
than requested due to the scheduling of other activity by the system.
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 execu‐
tion 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 execu‐
tion 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 causing
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 sig‐
nal is blocked from delivery, the results are unspecified.
If a signal-catching function interrupts usleep() and calls sig‐
longjmp() 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 unspec‐
ified. 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 val‐
ues. 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 ALSOalarm() , getitimer() , nanosleep() , sigaction() , sleep() ,
timer_create() , timer_delete() , timer_getoverrun() , the Base Defini‐
tions 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 Technology
-- 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)
