NetBSD/lib/libpthread/pthread_mutex.3

.\" $NetBSD: pthread_mutex.3,v 1.8 2016/07/05 10:04:17 wiz Exp $
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.\" ----------------------------------------------------------------------------
.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 * 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 .