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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.
.Pp
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.
.Pp
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.
.Bl -tag -width Er
.It Bq Er EINTR
.Nm
was interrupted by the delivery of a signal.
.It 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 alarm 3 ,
.Xr sigpause 3 ,
.Xr sleep 3 ,
.Xr ualarm 3
.Sh STANDARDS
The
.Fn usleep
function conforms to
.St -xpg4.2 .
.Sh HISTORY
The
.Fn usleep
function appeared in 
.Bx 4.3 .