usleep(2)

DESCRIPTION

The usleep() function will cause the calling thread to be suspended from execution until either the number of real-time microseconds specified 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 activities by the system, or because of the time spent in processing the call.

The useconds argument must be less than 1,000,000. 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 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 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's 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 will 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

On successful completion, usleep() returns 0. Otherwise, it returns -1 and sets errno to indicate the error.

ERRORS

The usleep() function may fail if:

APPLICATION USAGE

The usleep() function is included for its historical usage. The setitimer() function is preferred over this function. Multi-threaded applications are recommended to use nanosleep() instead of usleep(). usleep() is also a thread canceling point.

SEE ALSO

alarm(2), getitimer(2), nanosleep(2), sigaction(2), sleep(3C), timer_create(2), timer_delete(2), timer_getoverrun(2), timer_gettime(2), timer_settime(2), <unistd.h>.

CHANGE HISTORY

First released in Issue 4, Version 2.