[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 *file"
.Ft int
.Fn ftrylockfile "FILE *file"
.Ft void
.Fn funlockfile "FILE *file"
.Sh DESCRIPTION
These functions provide explicit application-level locking
of stdio FILE objects.
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 object for each operation.
.Pp
The
.Fn flockfile
function acquires an exclusive lock on the specified object.
If another thread has already locked the object,
.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 an object 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 object.
Each time
.Fn flockfile
is called on the object, the count is incremented,
and each time
.Fn funlockfile
is called on the object, 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 object 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
ad3c9f2a	40	.Fn flockfile "FILE *file"
9385eb3d	41	.Ft int
ad3c9f2a	42	.Fn ftrylockfile "FILE *file"
9385eb3d	43	.Ft void
ad3c9f2a	44	.Fn funlockfile "FILE *file"
9385eb3d	45	.Sh DESCRIPTION
ad3c9f2a A	46	These functions provide explicit application-level locking
ad3c9f2a A	47	of stdio FILE objects.
9385eb3d A	48	They can be used to avoid output from multiple threads being interspersed,
9385eb3d A	49	input being dispersed among multiple readers, and to avoid the overhead
ad3c9f2a	50	of locking the object for each operation.
9385eb3d A	51	.Pp
	52	The
	53	.Fn flockfile
ad3c9f2a A	54	function acquires an exclusive lock on the specified object.
ad3c9f2a A	55	If another thread has already locked the object,
9385eb3d A	56	.Fn flockfile
	57	will block until the lock is released.
	58	.Pp
	59	The
	60	.Fn ftrylockfile
	61	function is a non-blocking version of
	62	.Fn flockfile ;
	63	if the lock cannot be acquired immediately,
	64	.Fn ftrylockfile
	65	returns non-zero instead of blocking.
	66	.Pp
	67	The
	68	.Fn funlockfile
ad3c9f2a	69	function releases the lock on an object acquired by an earlier call to
9385eb3d A	70	.Fn flockfile
	71	or
	72	.Fn ftrylockfile .
	73	.Pp
	74	These functions behave as if there is a lock count associated
ad3c9f2a	75	with each object.
9385eb3d A	76	Each time
9385eb3d A	77	.Fn flockfile
ad3c9f2a	78	is called on the object, the count is incremented,
9385eb3d A	79	and each time
9385eb3d A	80	.Fn funlockfile
ad3c9f2a	81	is called on the object, the count is decremented.
9385eb3d A	82	The lock is only actually released when the count reaches zero.
	83	.Sh RETURN VALUES
	84	The
	85	.Fn flockfile
	86	and
	87	.Fn funlockfile
	88	functions return no value.
	89	.Pp
	90	The
	91	.Fn ftrylockfile
	92	function
ad3c9f2a	93	returns zero if the object was successfully locked,
9385eb3d A	94	non-zero otherwise.
	95	.Sh SEE ALSO
	96	.Xr getc_unlocked 3 ,
	97	.Xr putc_unlocked 3
	98	.Sh STANDARDS
	99	The
	100	.Fn flockfile ,
ad3c9f2a	101	.Fn ftrylockfile ,
9385eb3d A	102	and
	103	.Fn funlockfile
	104	functions conform to
	105	.St -p1003.1-2001 .