freebsd man page for usleep

USLEEP(3)						   BSD Library Functions Manual 						 USLEEP(3)

NAME
     usleep -- suspend process execution for an interval measured in microseconds

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     int
     usleep(useconds_t microseconds);

DESCRIPTION
     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.

RETURN VALUES
     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.

ERRORS
     The usleep() function will fail if:

     [EINTR]		A signal was delivered to the process and its action was to invoke a signal-catching function.

SEE ALSO
     nanosleep(2), sleep(3)

HISTORY
     The usleep() function appeared in 4.3BSD.

BSD
								 February 13, 1998							       BSD