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.Dd November 4, 1997 .Dt USLEEP 3 .Os BSD 4.3 .Sh NAME .Nm usleep .Nd suspend execution for interval of microseconds .Sh SYNOPSIS .Fd #include <unistd.h> .Ft int .Fn usleep "useconds_t microseconds" .Sh DESCRIPTION The .Fn usleep function suspends execution of the calling process for .Fa microseconds of time. System activity or time spent in processing the call may lengthen the sleep slightly.
p This routine is implemented using .Xr nanosleep 2 ; it requires one system call each time it is invoked. A similar but less compatible function can be obtained with a single .Xr select 2 ; such a function would not restart after signals, and also does not interfere with other uses of .Xr setitimer (not that .Fn usleep interferes with interval timers anymore.) .Sh RETURN VALUE If the .Fn usleep function returns because the requested time has elapsed, the value returned will be zero.
p If the .Fn usleep function returns due to the delivery of a signal, the value returned will be the -1, and the global variable .Va errno will be set to indicate the interruption. .Sh ERRORS If any of the following conditions occur, the .Nm function shall return -1 and set .Va errno to the corresponding value. l -tag -width Er t Bq Er EINTR .Nm was interrupted by the delivery of a signal. t Bq Er EINVAL .Fa useconds specified a value of 1,000,000 or more microseconds. .El .Sh SEE ALSO .Xr getitimer 2 , .Xr nanosleep 2 , .Xr setitimer 2 , .Xr sigpause 2 , .Xr alarm 3 .Xr sleep 3 , .Xr ualarm 3 , .Sh STANDARDS The .Fn function conforms to .St -xpg4.2 . .Sh HISTORY The .Fn usleep function appeared in x 4.3 .