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.\" $FreeBSD$ 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 LIBRARY 35.Lb libc_r 36.Lb libpthread 37.Lb libthr 38.Sh SYNOPSIS 39.In pthread.h 40.Ft int 41.Fn pthread_rwlock_wrlock "pthread_rwlock_t *lock" 42.Ft int 43.Fn pthread_rwlock_trywrlock "pthread_rwlock_t *lock" 44.Sh DESCRIPTION 45The 46.Fn pthread_rwlock_wrlock 47function blocks until a write lock can be acquired against 48.Fa lock . 49The 50.Fn pthread_rwlock_trywrlock 51function performs the same action, but does not block if the lock 52cannot be immediately obtained. 53.Pp 54The results are undefined if the calling thread already holds the 55lock at the time the call is made. 56.Sh IMPLEMENTATION NOTES 57To prevent writer starvation, writers are favored over readers. 58.Sh RETURN VALUES 59If successful, the 60.Fn pthread_rwlock_wrlock 61and 62.Fn pthread_rwlock_trywrlock 63functions will return zero. 64Otherwise an error number will be returned 65to indicate the error. 66.Sh ERRORS 67The 68.Fn pthread_rwlock_trywrlock 69function will fail if: 70.Bl -tag -width Er 71.It Bq Er EBUSY 72The calling thread is not able to acquire the lock without blocking. 73.El 74.Pp 75The 76.Fn pthread_rwlock_wrlock 77and 78.Fn pthread_rwlock_trywrlock 79functions may fail if: 80.Bl -tag -width Er 81.It Bq Er EDEADLK 82The calling thread already owns the read/write lock (for reading 83or writing). 84.It Bq Er EINVAL 85The value specified by 86.Fa lock 87is invalid. 88.It Bq Er ENOMEM 89Insufficient memory exists to initialize the lock (applies to 90statically initialized locks only). 91.El 92.Sh SEE ALSO 93.Xr pthread_rwlock_init 3 , 94.Xr pthread_rwlock_rdlock 3 , 95.Xr pthread_rwlock_tryrdlock 3 , 96.Xr pthread_rwlock_unlock 3 97.Sh STANDARDS 98The 99.Fn pthread_rwlock_wrlock 100and 101.Fn pthread_rwlock_trywrlock 102functions are expected to conform to 103.St -susv2 . 104.Sh HISTORY 105The 106.Fn pthread_rwlock_wrlock 107function first appeared in 108.Fx 3.0 . 109