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