1.\" $NetBSD: usleep.3,v 1.22 2024/05/15 13:12:04 riastradh Exp $ 2.\" 3.\" Copyright (c) 1986, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)usleep.3 8.1 (Berkeley) 6/4/93 31.\" 32.Dd April 22, 2024 33.Dt USLEEP 3 34.Os 35.Sh NAME 36.Nm usleep 37.Nd suspend execution for interval of microseconds 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In unistd.h 42.Ft int 43.Fn usleep "useconds_t microseconds" 44.Sh DESCRIPTION 45.Bf -symbolic 46This interface is obsoleted by 47.Xr nanosleep 2 . 48.Ef 49.Pp 50The 51.Fn usleep 52function 53suspends execution of the calling process 54until either the number of microseconds specified by 55.Fa microseconds 56have elapsed or a signal is delivered to the calling process and its 57action is to invoke a signal catching function or to terminate the 58process. 59The suspension time may be longer than requested due to the 60scheduling of other activity by the system. 61.Sh RETURN VALUES 62On successful completion, 63.Fn usleep 64returns 0. 65Otherwise, it returns \-1 and sets 66.Va errno 67to indicate the error. 68.Sh ERRORS 69The 70.Fn usleep 71function may fail if: 72.Bl -tag -width Er 73.It Bq Er EINTR 74.Nm 75was interrupted by the delivery of a signal. 76.El 77.Sh SEE ALSO 78.Xr nanosleep 2 , 79.Xr sleep 3 80.Sh STANDARDS 81The 82.Fn usleep 83function conforms to 84.St -xpg4.2 . 85It later appeared in the 86.Tn POSIX 87standard, but in 88.St -p1003.1-2004 89it was marked as legacy and the use of 90.Xr nanosleep 2 91was recommended instead. 92The 93.St -p1003.1-2008 94revision removed 95.Fn usleep 96from the specification. 97.Sh HISTORY 98The 99.Fn usleep 100function appeared in 101.Bx 4.3 . 102.Sh CAVEATS 103In 104.St -p1003.1-2004 , 105.Nm 106was limited to values of 107.Fa microseconds 108less than one million. 109Some implementations, including 110.Nx 111before 10.1, fail immediately with 112.Er EINVAL 113\(em and don't sleep at all \(em if 114.Fa microseconds 115is one million or greater. 116