Synopsis
#include <unistd.h>
int usleep(useconds_t useconds);
Status
Partially implemented
Conformance
IEEE Std 1003.1, 2004
Description
The usleep() function shall 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 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 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 thread'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 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()
The usleep() function need not be reentrant. A function that is not required to be reentrant is not required to be
thread-safe.
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.
Tests
Untested
Known bugs
None