[apple/libc.git] / pthreads / pthread_rwlock_wrlock.3

.\" Copyright (c) 1998 Alex Nash
.\" 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_r/man/pthread_rwlock_wrlock.3,v 1.4 2001/10/01 16:09:09 ru Exp $
.\"
.Dd August 4, 1998
.Dt PTHREAD_RWLOCK_WRLOCK 3
.Os
.Sh NAME
.Nm pthread_rwlock_trywrlock ,
.Nm pthread_rwlock_wrlock
.Nd acquire a read/write lock for writing
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fo pthread_rwlock_trywrlock
.Fa "pthread_rwlock_t *rwlock"
.Fc
.Ft int
.Fo pthread_rwlock_wrlock
.Fa "pthread_rwlock_t *rwlock"
.Fc
.Sh DESCRIPTION
The
.Fn pthread_rwlock_wrlock
function blocks until a write lock can be acquired against
.Fa rwlock .
The
.Fn pthread_rwlock_trywrlock
function performs the same action, but does not block if the lock
cannot be immediately obtained.
.Pp
The results are undefined if the calling thread already holds the
lock at the time the call is made.
.Sh IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers.
.Sh RETURN VALUES
If successful, the
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions will return zero.
Otherwise, an error number will be returned  to indicate the error.
.Sh SEE ALSO
.Xr pthread_rwlock_trywrlock 3 ,
.Xr pthread_rwlock_unlock 3 ,
.Xr pthread_rwlock_wrlock 3
.Sh STANDARDS
The
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions are expected to conform to
.St -susv2 .
.Sh ERRORS
The
.Fn pthread_rwlock_trywrlock
function will fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
The calling thread is not able to acquire the lock without blocking.
.El
.Pp
The
.Fn pthread_rwlock_wrlock
and
.Fn pthread_rwlock_trywrlock
functions may fail if:
.Bl -tag -width Er
.It Bq Er EDEADLK
The calling thread already owns the read/write lock (for reading
or writing).
.It Bq Er EINVAL
The value specified by
.Fa rwlock
is invalid.
.It Bq Er ENOMEM
Insufficient memory exists to initialize the lock (applies to
statically initialized locks only).
.El
.Sh HISTORY
The
.Fn pthread_rwlock_wrlock
function first appeared in
.Fx 3.0 .
Commit	Line	Data
5b2abdfb A	1	.\" Copyright (c) 1998 Alex Nash
	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_r/man/pthread_rwlock_wrlock.3,v 1.4 2001/10/01 16:09:09 ru Exp $
	26	.\"
	27	.Dd August 4, 1998
	28	.Dt PTHREAD_RWLOCK_WRLOCK 3
	29	.Os
	30	.Sh NAME
224c7076 A	31	.Nm pthread_rwlock_trywrlock ,
224c7076 A	32	.Nm pthread_rwlock_wrlock
5b2abdfb A	33	.Nd acquire a read/write lock for writing
	34	.Sh SYNOPSIS
	35	.In pthread.h
	36	.Ft int
224c7076 A	37	.Fo pthread_rwlock_trywrlock
	38	.Fa "pthread_rwlock_t *rwlock"
	39	.Fc
5b2abdfb	40	.Ft int
224c7076 A	41	.Fo pthread_rwlock_wrlock
	42	.Fa "pthread_rwlock_t *rwlock"
	43	.Fc
5b2abdfb A	44	.Sh DESCRIPTION
	45	The
	46	.Fn pthread_rwlock_wrlock
	47	function blocks until a write lock can be acquired against
224c7076	48	.Fa rwlock .
5b2abdfb A	49	The
	50	.Fn pthread_rwlock_trywrlock
	51	function performs the same action, but does not block if the lock
	52	cannot be immediately obtained.
	53	.Pp
	54	The results are undefined if the calling thread already holds the
	55	lock at the time the call is made.
	56	.Sh IMPLEMENTATION NOTES
	57	To prevent writer starvation, writers are favored over readers.
	58	.Sh RETURN VALUES
	59	If successful, the
	60	.Fn pthread_rwlock_wrlock
	61	and
	62	.Fn pthread_rwlock_trywrlock
224c7076 A	63	functions will return zero.
224c7076 A	64	Otherwise, an error number will be returned to indicate the error.
5b2abdfb A	65	.Sh SEE ALSO
	66	.Xr pthread_rwlock_trywrlock 3 ,
	67	.Xr pthread_rwlock_unlock 3 ,
	68	.Xr pthread_rwlock_wrlock 3
	69	.Sh STANDARDS
	70	The
	71	.Fn pthread_rwlock_wrlock
	72	and
	73	.Fn pthread_rwlock_trywrlock
	74	functions are expected to conform to
	75	.St -susv2 .
	76	.Sh ERRORS
	77	The
	78	.Fn pthread_rwlock_trywrlock
	79	function will fail if:
	80	.Bl -tag -width Er
	81	.It Bq Er EBUSY
	82	The calling thread is not able to acquire the lock without blocking.
	83	.El
	84	.Pp
	85	The
	86	.Fn pthread_rwlock_wrlock
	87	and
	88	.Fn pthread_rwlock_trywrlock
	89	functions may fail if:
	90	.Bl -tag -width Er
	91	.It Bq Er EDEADLK
	92	The calling thread already owns the read/write lock (for reading
	93	or writing).
	94	.It Bq Er EINVAL
	95	The value specified by
224c7076	96	.Fa rwlock
5b2abdfb A	97	is invalid.
	98	.It Bq Er ENOMEM
	99	Insufficient memory exists to initialize the lock (applies to
	100	statically initialized locks only).
	101	.El
	102	.Sh HISTORY
	103	The
	104	.Fn pthread_rwlock_wrlock
	105	function first appeared in
	106	.Fx 3.0 .