.\" $NetBSD: pthread_mutex.3,v 1.9 2016/10/30 23:26:33 kamil 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 .\" 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 June 12, 2016 .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" .Ft int .Fn pthread_mutex_timedlock "pthread_mutex_t *__restrict mutex" "const struct timespec *__restrict timeout" .Ft int .Fn pthread_mutex_getprioceiling "const pthread_mutex_t * __restrict mutex" "int * __restrict prioceiling" .Ft int .Fn pthread_mutex_setprioceiling "pthread_mutex_t * __restrict mutex" \ "int prioceiling" "int * __restrict old_ceiling" .\" ---------------------------------------------------------------------------- .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. .Pp .\" ----- The .Fn pthread_mutex_timedlock function shall lock the mutex object referenced by .Fa mutex . If the mutex is already locked, the calling thread shall block until the mutex becomes available in the .Fn pthread_mutex_lock function. If the mutex cannot be locked without waiting for another thread to unlock the mutex, this wait shall be terminated when the specified timeout expires. The timeout shall expire when the absolute time specified by .Fa timeout passes, as measured by the clock on which timeouts are based. .Pp .\" ----- The .Fn pthread_mutex_getprioceiling function shall return the current priority ceiling of the mutex. .Pp .\" ----- The .Fn pthread_mutex_setprioceiling function shall either lock the mutex if it is unlocked, or block until it can sucessfully lock the mutex, then it shall change the mutex's priority ceiling and release the mutex. When the change is successful, the previous value of the priority ceiling shall be returned in .Fa old_ceiling . The process of locking the mutex need not adhere to the priority protect protocol. If .Fn pthread_mutex_setprioceiling function fails, the mutex priority ceiling shall not be changed. .\" ---------------------------------------------------------------------------- .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 .Pp .\" ----- .Fn pthread_mutex_timedlock may fail if: .Bl -tag -width Er .It Bq Er EINVAL The mutex was created with the protocol attribute having the value .Dv PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex current priority ceiling; or the process or thread would have blocked, and the .Fa timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million. .It Bq Er ETIMEDOUT The mutex could not be locked before the specified timeout expired. .El .Pp .\" ----- The .Fn pthread_mutex_getprioceiling and .Fn pthread_mutex_setprioceiling functions may fail if: .Bl -tag -width Er .It Bq Er EINVAL The priority requested by .Fa prioceiling is out of range; or the value specified by .Fa mutex does not refer to a currently existing mutex. .It Bq Er EPERM The caller does not have the privilege to perform the operation. .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 .