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.Dd January 10, 2003 26.Dt FLOCKFILE 3 27.Os 28.Sh NAME 29.Nm flockfile , 30.Nm ftrylockfile , 31.Nm funlockfile 32.Nd "stdio locking functions" 33.Sh LIBRARY 34.Lb libc 35.Sh SYNOPSIS 36.In stdio.h 37.Ft void 38.Fn flockfile "FILE *stream" 39.Ft int 40.Fn ftrylockfile "FILE *stream" 41.Ft void 42.Fn funlockfile "FILE *stream" 43.Sh DESCRIPTION 44These functions provide explicit application-level locking of stdio streams. 45They can be used to avoid output from multiple threads being interspersed, 46input being dispersed among multiple readers, and to avoid the overhead 47of locking the stream for each operation. 48.Pp 49The 50.Fn flockfile 51function acquires an exclusive lock on the specified stream. 52If another thread has already locked the stream, 53.Fn flockfile 54will block until the lock is released. 55.Pp 56The 57.Fn ftrylockfile 58function is a non-blocking version of 59.Fn flockfile ; 60if the lock cannot be acquired immediately, 61.Fn ftrylockfile 62returns non-zero instead of blocking. 63.Pp 64The 65.Fn funlockfile 66function releases the lock on a stream acquired by an earlier call to 67.Fn flockfile 68or 69.Fn ftrylockfile . 70.Pp 71These functions behave as if there is a lock count associated 72with each stream. 73Each time 74.Fn flockfile 75is called on the stream, the count is incremented, 76and each time 77.Fn funlockfile 78is called on the stream, the count is decremented. 79The lock is only actually released when the count reaches zero. 80.Sh RETURN VALUES 81The 82.Fn flockfile 83and 84.Fn funlockfile 85functions return no value. 86.Pp 87The 88.Fn ftrylockfile 89function 90returns zero if the stream was successfully locked, 91non-zero otherwise. 92.Sh SEE ALSO 93.Xr getc_unlocked 3 , 94.Xr putc_unlocked 3 95.Sh STANDARDS 96The 97.Fn flockfile , 98.Fn ftrylockfile 99and 100.Fn funlockfile 101functions conform to 102.St -p1003.1-2001 . 103