1.\" Copyright (c) 2003 Tim J. Robbins 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd January 10, 2003 28.Dt FLOCKFILE 3 29.Os 30.Sh NAME 31.Nm flockfile , 32.Nm ftrylockfile , 33.Nm funlockfile 34.Nd "stdio locking functions" 35.Sh LIBRARY 36.Lb libc 37.Sh SYNOPSIS 38.In stdio.h 39.Ft void 40.Fn flockfile "FILE *stream" 41.Ft int 42.Fn ftrylockfile "FILE *stream" 43.Ft void 44.Fn funlockfile "FILE *stream" 45.Sh DESCRIPTION 46These functions provide explicit application-level locking of stdio streams. 47They can be used to avoid output from multiple threads being interspersed, 48input being dispersed among multiple readers, and to avoid the overhead 49of locking the stream for each operation. 50.Pp 51The 52.Fn flockfile 53function acquires an exclusive lock on the specified stream. 54If another thread has already locked the stream, 55.Fn flockfile 56will block until the lock is released. 57.Pp 58The 59.Fn ftrylockfile 60function is a non-blocking version of 61.Fn flockfile ; 62if the lock cannot be acquired immediately, 63.Fn ftrylockfile 64returns non-zero instead of blocking. 65.Pp 66The 67.Fn funlockfile 68function releases the lock on a stream acquired by an earlier call to 69.Fn flockfile 70or 71.Fn ftrylockfile . 72.Pp 73These functions behave as if there is a lock count associated 74with each stream. 75Each time 76.Fn flockfile 77is called on the stream, the count is incremented, 78and each time 79.Fn funlockfile 80is called on the stream, the count is decremented. 81The lock is only actually released when the count reaches zero. 82.Sh RETURN VALUES 83The 84.Fn flockfile 85and 86.Fn funlockfile 87functions return no value. 88.Pp 89The 90.Fn ftrylockfile 91function 92returns zero if the stream was successfully locked, 93non-zero otherwise. 94.Sh SEE ALSO 95.Xr getc_unlocked 3 , 96.Xr putc_unlocked 3 97.Sh STANDARDS 98The 99.Fn flockfile , 100.Fn ftrylockfile 101and 102.Fn funlockfile 103functions conform to 104.St -p1003.1-2001 . 105