[apple/libc.git] / stdio / FreeBSD / flockfile.3

.\" Copyright (c) 2003 Tim J. Robbins
.\" All rights reserved.
.\"
.\" 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 AUTHOR 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 AUTHOR 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.
.\"
.\" $FreeBSD: src/lib/libc/stdio/flockfile.3,v 1.3 2003/01/13 01:29:14 tjr Exp $
.\"
.Dd January 10, 2003
.Dt FLOCKFILE 3
.Os
.Sh NAME
.Nm flockfile ,
.Nm ftrylockfile ,
.Nm funlockfile
.Nd "stdio locking functions"
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft void
.Fn flockfile "FILE *stream"
.Ft int
.Fn ftrylockfile "FILE *stream"
.Ft void
.Fn funlockfile "FILE *stream"
.Sh DESCRIPTION
These functions provide explicit application-level locking of stdio streams.
They can be used to avoid output from multiple threads being interspersed,
input being dispersed among multiple readers, and to avoid the overhead
of locking the stream for each operation.
.Pp
The
.Fn flockfile
function acquires an exclusive lock on the specified stream.
If another thread has already locked the stream,
.Fn flockfile
will block until the lock is released.
.Pp
The
.Fn ftrylockfile
function is a non-blocking version of
.Fn flockfile ;
if the lock cannot be acquired immediately,
.Fn ftrylockfile
returns non-zero instead of blocking.
.Pp
The
.Fn funlockfile
function releases the lock on a stream acquired by an earlier call to
.Fn flockfile
or
.Fn ftrylockfile .
.Pp
These functions behave as if there is a lock count associated
with each stream.
Each time
.Fn flockfile
is called on the stream, the count is incremented,
and each time
.Fn funlockfile
is called on the stream, the count is decremented.
The lock is only actually released when the count reaches zero.
.Sh RETURN VALUES
The
.Fn flockfile
and
.Fn funlockfile
functions return no value.
.Pp
The
.Fn ftrylockfile
function
returns zero if the stream was successfully locked,
non-zero otherwise.
.Sh SEE ALSO
.Xr getc_unlocked 3 ,
.Xr putc_unlocked 3
.Sh STANDARDS
The
.Fn flockfile ,
.Fn ftrylockfile
and
.Fn funlockfile
functions conform to
.St -p1003.1-2001 .
Commit	Line	Data
9385eb3d A	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: src/lib/libc/stdio/flockfile.3,v 1.3 2003/01/13 01:29:14 tjr Exp $
	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
	46	These functions provide explicit application-level locking of stdio streams.
	47	They can be used to avoid output from multiple threads being interspersed,
	48	input being dispersed among multiple readers, and to avoid the overhead
	49	of locking the stream for each operation.
	50	.Pp
	51	The
	52	.Fn flockfile
	53	function acquires an exclusive lock on the specified stream.
	54	If another thread has already locked the stream,
	55	.Fn flockfile
	56	will block until the lock is released.
	57	.Pp
	58	The
	59	.Fn ftrylockfile
	60	function is a non-blocking version of
	61	.Fn flockfile ;
	62	if the lock cannot be acquired immediately,
	63	.Fn ftrylockfile
	64	returns non-zero instead of blocking.
65	.Pp
66	The
67	.Fn funlockfile
68	function releases the lock on a stream acquired by an earlier call to
69	.Fn flockfile
70	or
71	.Fn ftrylockfile .
72	.Pp
73	These functions behave as if there is a lock count associated
74	with each stream.
75	Each time
76	.Fn flockfile
77	is called on the stream, the count is incremented,
78	and each time
79	.Fn funlockfile
80	is called on the stream, the count is decremented.
81	The lock is only actually released when the count reaches zero.
82	.Sh RETURN VALUES
83	The
84	.Fn flockfile
85	and
86	.Fn funlockfile
87	functions return no value.
88	.Pp
89	The
90	.Fn ftrylockfile
91	function
92	returns zero if the stream was successfully locked,
93	non-zero otherwise.
94	.Sh SEE ALSO
95	.Xr getc_unlocked 3 ,
96	.Xr putc_unlocked 3
97	.Sh STANDARDS
98	The
99	.Fn flockfile ,
100	.Fn ftrylockfile
101	and
102	.Fn funlockfile
103	functions conform to
104	.St -p1003.1-2001 .