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