1.\" $NetBSD: pthread_mutex.3,v 1.6 2012/11/12 23:11:05 uwe Exp $ 2.\" 3.\" Copyright (c) 2002, 2010 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 16.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 17.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 18.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 19.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 20.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 21.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 22.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 23.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 24.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 25.\" POSSIBILITY OF SUCH DAMAGE. 26.\" 27.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com> 28.\" All rights reserved. 29.\" 30.\" Redistribution and use in source and binary forms, with or without 31.\" modification, are permitted provided that the following conditions 32.\" are met: 33.\" 1. Redistributions of source code must retain the above copyright 34.\" notice, this list of conditions and the following disclaimer. 35.\" 2. Redistributions in binary form must reproduce the above copyright 36.\" notice, this list of conditions and the following disclaimer in the 37.\" documentation and/or other materials provided with the distribution. 38.\" 3. Neither the name of the author nor the names of any co-contributors 39.\" may be used to endorse or promote products derived from this software 40.\" without specific prior written permission. 41.\" 42.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND 43.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 44.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 45.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 46.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 47.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 48.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 49.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 50.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 51.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 52.\" SUCH DAMAGE. 53.\" 54.\" ---------------------------------------------------------------------------- 55.Dd July 8, 2010 56.Dt PTHREAD_MUTEX 3 57.Os 58.Sh NAME 59.Nm pthread_mutex 60.Nd mutual exclusion primitives 61.Sh LIBRARY 62.Lb libpthread 63.\" ---------------------------------------------------------------------------- 64.Sh SYNOPSIS 65.In pthread.h 66.Ft int 67.Fn pthread_mutex_init "pthread_mutex_t * restrict mutex" \ 68"const pthread_mutexattr_t * restrict attr" 69.Vt pthread_mutex_t mutex No = Dv PTHREAD_MUTEX_INITIALIZER; 70.Ft int 71.Fn pthread_mutex_destroy "pthread_mutex_t *mutex" 72.Ft int 73.Fn pthread_mutex_lock "pthread_mutex_t *mutex" 74.Ft int 75.Fn pthread_mutex_trylock "pthread_mutex_t *mutex" 76.Ft int 77.Fn pthread_mutex_unlock "pthread_mutex_t *mutex" 78.\" ---------------------------------------------------------------------------- 79.Sh DESCRIPTION 80The 81.Fn pthread_mutex_init 82function creates a new mutex, with attributes specified with 83.Fa attr . 84If 85.Fa attr 86is 87.Dv NULL , 88the default attributes are used. 89.Pp 90The macro 91.Dv PTHREAD_MUTEX_INITIALIZER 92can be used to initialize a mutex when the default attributes are 93appropriate and the mutex can be statically allocated. 94The behavior is similar to 95.Fn pthread_mutex_init 96with 97.Fa attr 98specified as 99.Dv NULL , 100except that no error checking is done. 101.Pp 102.\" ----- 103The 104.Fn pthread_mutex_destroy 105function frees the resources allocated for 106.Fa mutex . 107It is possible to reinitialize a destroyed mutex, but undefined 108behavior may follow if the destroyed object is otherwise referenced. 109.Pp 110.\" ----- 111The 112.Fn pthread_mutex_lock 113function locks 114.Fa mutex . 115If the mutex is already locked, the calling thread will block until the 116mutex becomes available. 117The error conditions may vary depending on the type of the mutex; see 118.Xr pthread_mutexattr 3 119for additional details. 120.Pp 121The 122.Fn pthread_mutex_trylock 123function locks 124.Fa mutex . 125If the mutex is already locked, 126.Fn pthread_mutex_trylock 127will not block waiting for the mutex, but will return an error condition. 128.Pp 129.\" ----- 130The 131.Fn pthread_mutex_unlock 132function unlocks an acquired 133.Fa mutex . 134When operating with the default mutex type, 135undefined behavior follows if a thread tries to unlock a mutex 136that has not been locked by it, or if a thread tries to release 137a mutex that is already unlocked. 138.\" ---------------------------------------------------------------------------- 139.Sh RETURN VALUES 140Upon success all described functions return zero. 141Otherwise, an error number will be returned to indicate the error. 142.Sh ERRORS 143.Fn pthread_mutex_init 144may fail if: 145.Bl -tag -width Er 146.It Bq Er EAGAIN 147The system lacks the resources to initialize another mutex. 148.It Bq Er EINVAL 149The value specified by 150.Fa attr 151is invalid. 152.It Bq Er ENOMEM 153The process cannot allocate enough memory to initialize another mutex. 154.El 155.Pp 156.\" ----- 157.Fn pthread_mutex_destroy 158may fail if: 159.Bl -tag -width Er 160.It Bq Er EBUSY 161.Fa Mutex 162is locked by another thread. 163.It Bq Er EINVAL 164The value specified by 165.Fa mutex 166is invalid. 167.El 168.Pp 169.\" ----- 170.Fn pthread_mutex_lock 171may fail if: 172.Bl -tag -width Er 173.It Bq Er EDEADLK 174A deadlock would occur if the thread blocked waiting for 175.Fa mutex . 176.It Bq Er EINVAL 177The value specified by 178.Fa mutex 179is invalid. 180.El 181.Pp 182.Fn pthread_mutex_trylock 183may fail if: 184.Bl -tag -width Er 185.It Bq Er EBUSY 186.Fa Mutex 187is already locked. 188.It Bq Er EINVAL 189The value specified by 190.Fa mutex 191is invalid. 192.El 193.Pp 194.\" ----- 195.Fn pthread_mutex_unlock 196may fail if: 197.Bl -tag -width Er 198.It Bq Er EINVAL 199The value specified by 200.Fa mutex 201is invalid. 202.It Bq Er EPERM 203The current thread does not hold a lock on 204.Fa mutex . 205.El 206.\" ---------------------------------------------------------------------------- 207.Sh SEE ALSO 208.Xr pthread 3 , 209.Xr pthread_barrier 3 , 210.Xr pthread_cond 3 , 211.Xr pthread_mutexattr 3 , 212.Xr pthread_rwlock 3 , 213.Xr pthread_spin 3 214.\" ---------------------------------------------------------------------------- 215.Sh STANDARDS 216These functions conform to 217.St -p1003.1-2001 . 218