USLEEP(P) POSIX Programmer's Manual USLEEP(P)
usleep - suspend execution for an interval
int usleep(useconds_t useconds);
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-
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:
Upon successful completion, usleep() shall return 0; otherwise, it shall return -1 and set errno to indicate the error.
The usleep() function may fail if:
EINVAL The time interval specified one million or more microseconds.
The following sections are informative.
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.
alarm() , getitimer() , nanosleep() , sigaction() , sleep() , timer_create() , timer_delete() , timer_getoverrun() , the Base Definitions
volume of IEEE Std 1003.1-2001, <unistd.h>
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 .
/The Open Group 2003 USLEEP(P)