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.\" $NetBSD: pthread_mutex.3,v 1.6 2012/11/12 23:11:05 uwe Exp $
.\"
.\" Copyright (c) 2002, 2010 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the author nor the names of any co-contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" ----------------------------------------------------------------------------
.Dd July 8, 2010
.Dt PTHREAD_MUTEX 3
.Os
.Sh NAME
.Nm pthread_mutex
.Nd mutual exclusion primitives
.Sh LIBRARY
.Lb libpthread
.\" ----------------------------------------------------------------------------
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_mutex_init "pthread_mutex_t * restrict mutex" \
"const pthread_mutexattr_t * restrict attr"
.Vt pthread_mutex_t mutex No = Dv PTHREAD_MUTEX_INITIALIZER;
.Ft int
.Fn pthread_mutex_destroy "pthread_mutex_t *mutex"
.Ft int
.Fn pthread_mutex_lock "pthread_mutex_t *mutex"
.Ft int
.Fn pthread_mutex_trylock "pthread_mutex_t *mutex"
.Ft int
.Fn pthread_mutex_unlock "pthread_mutex_t *mutex"
.\" ----------------------------------------------------------------------------
.Sh DESCRIPTION
The
.Fn pthread_mutex_init
function creates a new mutex, with attributes specified with
.Fa attr .
If
.Fa attr
is
.Dv NULL ,
the default attributes are used.
.Pp
The macro
.Dv PTHREAD_MUTEX_INITIALIZER
can be used to initialize a mutex when the default attributes are
appropriate and the mutex can be statically allocated.
The behavior is similar to
.Fn pthread_mutex_init
with
.Fa attr
specified as
.Dv NULL ,
except that no error checking is done.
.Pp
.\" -----
The
.Fn pthread_mutex_destroy
function frees the resources allocated for
.Fa mutex .
It is possible to reinitialize a destroyed mutex, but undefined
behavior may follow if the destroyed object is otherwise referenced.
.Pp
.\" -----
The
.Fn pthread_mutex_lock
function locks
.Fa mutex .
If the mutex is already locked, the calling thread will block until the
mutex becomes available.
The error conditions may vary depending on the type of the mutex; see
.Xr pthread_mutexattr 3
for additional details.
.Pp
The
.Fn pthread_mutex_trylock
function locks
.Fa mutex .
If the mutex is already locked,
.Fn pthread_mutex_trylock
will not block waiting for the mutex, but will return an error condition.
.Pp
.\" -----
The
.Fn pthread_mutex_unlock
function unlocks an acquired
.Fa mutex .
When operating with the default mutex type,
undefined behavior follows if a thread tries to unlock a mutex
that has not been locked by it, or if a thread tries to release
a mutex that is already unlocked.
.\" ----------------------------------------------------------------------------
.Sh RETURN VALUES
Upon success all described functions return zero.
Otherwise, an error number will be returned to indicate the error.
.Sh ERRORS
.Fn pthread_mutex_init
may fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
The system lacks the resources to initialize another mutex.
.It Bq Er EINVAL
The value specified by
.Fa attr
is invalid.
.It Bq Er ENOMEM
The process cannot allocate enough memory to initialize another mutex.
.El
.Pp
.\" -----
.Fn pthread_mutex_destroy
may fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
.Fa Mutex
is locked by another thread.
.It Bq Er EINVAL
The value specified by
.Fa mutex
is invalid.
.El
.Pp
.\" -----
.Fn pthread_mutex_lock
may fail if:
.Bl -tag -width Er
.It Bq Er EDEADLK
A deadlock would occur if the thread blocked waiting for
.Fa mutex .
.It Bq Er EINVAL
The value specified by
.Fa mutex
is invalid.
.El
.Pp
.Fn pthread_mutex_trylock
may fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
.Fa Mutex
is already locked.
.It Bq Er EINVAL
The value specified by
.Fa mutex
is invalid.
.El
.Pp
.\" -----
.Fn pthread_mutex_unlock
may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified by
.Fa mutex
is invalid.
.It Bq Er EPERM
The current thread does not hold a lock on
.Fa mutex .
.El
.\" ----------------------------------------------------------------------------
.Sh SEE ALSO
.Xr pthread 3 ,
.Xr pthread_barrier 3 ,
.Xr pthread_cond 3 ,
.Xr pthread_mutexattr 3 ,
.Xr pthread_rwlock 3 ,
.Xr pthread_spin 3
.\" ----------------------------------------------------------------------------
.Sh STANDARDS
These functions conform to
.St -p1003.1-2001 .
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