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f1a1da6c 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
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	18	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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	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	.\"
2546420a	25	.\" $FreeBSD$
f1a1da6c A	26	.\"
	27	.Dd August 4, 1998
	28	.Dt PTHREAD_RWLOCK_WRLOCK 3
	29	.Os
	30	.Sh NAME
2546420a A	31	.Nm pthread_rwlock_wrlock ,
2546420a A	32	.Nm pthread_rwlock_trywrlock
f1a1da6c A	33	.Nd acquire a read/write lock for writing
	34	.Sh SYNOPSIS
	35	.In pthread.h
	36	.Ft int
2546420a	37	.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock"
f1a1da6c	38	.Ft int
2546420a	39	.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock"
f1a1da6c A	40	.Sh DESCRIPTION
	41	The
	42	.Fn pthread_rwlock_wrlock
	43	function blocks until a write lock can be acquired against
2546420a	44	.Fa lock .
f1a1da6c A	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.
2546420a A	60	Otherwise an error number will be returned
2546420a A	61	to indicate the error.
f1a1da6c A	62	.Sh ERRORS
	63	The
	64	.Fn pthread_rwlock_trywrlock
	65	function will fail if:
	66	.Bl -tag -width Er
	67	.It Bq Er EBUSY
	68	The calling thread is not able to acquire the lock without blocking.
	69	.El
	70	.Pp
	71	The
	72	.Fn pthread_rwlock_wrlock
	73	and
	74	.Fn pthread_rwlock_trywrlock
	75	functions may fail if:
	76	.Bl -tag -width Er
	77	.It Bq Er EDEADLK
	78	The calling thread already owns the read/write lock (for reading
	79	or writing).
	80	.It Bq Er EINVAL
	81	The value specified by
2546420a	82	.Fa lock
f1a1da6c A	83	is invalid.
	84	.It Bq Er ENOMEM
	85	Insufficient memory exists to initialize the lock (applies to
	86	statically initialized locks only).
	87	.El
2546420a A	88	.Sh SEE ALSO
	89	.Xr pthread_rwlock_init 3 ,
	90	.Xr pthread_rwlock_rdlock 3 ,
	91	.Xr pthread_rwlock_tryrdlock 3 ,
	92	.Xr pthread_rwlock_unlock 3
	93	.Sh STANDARDS
	94	The
	95	.Fn pthread_rwlock_wrlock
	96	and
	97	.Fn pthread_rwlock_trywrlock
	98	functions are expected to conform to
	99	.St -susv2 .
f1a1da6c A	100	.Sh HISTORY
	101	The
	102	.Fn pthread_rwlock_wrlock
	103	function first appeared in
	104	.Fx 3.0 .