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Revision 1.4, Wed Apr 30 13:10:51 2008 UTC (11 years, 7 months ago) by martin
Convert TNF licenses to new 2 clause variant
.\" $NetBSD: flockfile.3,v 1.4 2008/04/30 13:10:51 martin Exp $ .\" .\" Copyright (c) 2003 The NetBSD Foundation, Inc. .\" All rights reserved. .\" .\" This code is derived from software contributed to The NetBSD Foundation .\" by Klaus Klein. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS .\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR .\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS .\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR .\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF .\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS .\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN .\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd January 28, 2003 .Dt FLOCKFILE 3 .Os .Sh NAME .Nm flockfile , .Nm ftrylockfile , .Nm funlockfile .Nd stdio stream locking functions .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In stdio.h .Ft void .Fn flockfile "FILE *file" .Ft int .Fn ftrylockfile "FILE *file" .Ft void .Fn funlockfile "FILE *file" .Sh DESCRIPTION The .Fn flockfile , .Fn ftrylockfile , and .Fn funlockfile functions provide applications with explicit control of locking of stdio stream objects. They can be used by a thread to execute a sequence of I/O operations as a unit, without interference from another thread. .Pp Locks on stdio streams are recursive, and a lock count is maintained. stdio streams are created unlocked, with a lock count of zero. After successful acquisition of the lock, its count is incremented to one, indicating locked state of the stdio stream. Each subsequent relock operation performed by the owner thread increments the lock count by one, and each subsequent unlock operation performed by the owner thread decrements the lock count by one, allowing matching lock and unlock operations to be nested. After its lock count is decremented to zero, the stdio stream returns to unlocked state, and ownership of the stdio stream is relinquished. .Pp The .Fn flockfile function acquires the ownership of .Fa file for the calling thread. If .Fa file is already owned by another thread, the calling thread is suspended until the acquisition is possible (i.e., .Fa file is relinquished again and the calling thread is scheduled to acquire it). .Pp The .Fn ftrylockfile function acquires the ownership of .Fa file for the calling thread only if .Fa file is available. .Pp The .Fn funlockfile function relinquishes the ownership of .Fa file previously granted to the calling thread. Only the current owner of .Fa file may .Fn funlockfile it. .Sh RETURN VALUES If successful, the .Fn ftrylockfile function returns 0. Otherwise, it returns non-zero to indicate that the lock cannot be acquired. .Sh SEE ALSO .Xr getc_unlocked 3 , .Xr getchar_unlocked 3 , .Xr putc_unlocked 3 , .Xr putchar_unlocked 3 .Sh STANDARDS The .Fn flockfile , .Fn ftrylockfile and .Fn funlockfile functions conform to .St -p1003.1-2001 . .Sh BUGS The design of these interfaces does not allow for addressing the problem of priority inversion.