FreeBSD 11.0 - man page for usleep (freebsd section 3)
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USLEEP(3) BSD Library Functions Manual USLEEP(3)
usleep -- suspend process execution for an interval measured in microseconds
Standard C Library (libc, -lc)
The usleep() function suspends execution of the calling process until either microseconds
microseconds have elapsed or a signal is delivered to the process and its action is to
invoke a signal-catching function or to terminate the process. System activity may lengthen
the sleep by an indeterminate amount.
This function is implemented using nanosleep(2) by pausing for microseconds microseconds or
until a signal occurs. Consequently, in this implementation, sleeping has no effect on the
state of process timers, and there is no special handling for SIGALRM.
The usleep() function returns the value 0 if successful; otherwise the value -1 is returned
and the global variable errno is set to indicate the error.
The usleep() function will fail if:
[EINTR] A signal was delivered to the process and its action was to invoke a sig-
The usleep() function appeared in 4.3BSD.
BSD February 13, 1998 BSD
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