NetBSD/lib/libpthread/pthread_mutex.3

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.\" $NetBSD: pthread_mutex.3,v 1.5 2010/07/09 10:55:11 wiz Exp $
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.\" Copyright (c) 1997 Brian Cully <shmit@kublai.com>
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.\" modification, are permitted provided that the following conditions
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.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
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.\" ----------------------------------------------------------------------------
.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"
.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"
.Pp
.Va pthread_mutex_t mutex = Dv PTHREAD_MUTEX_INITIALIZER;
.\" ----------------------------------------------------------------------------
.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 .