\" $NetBSD: pthread_mutex.3,v 1.12 2025/02/10 20:40:55 riastradh Exp $
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\" ----------------------------------------------------------------------------
Dd June 12, 2016
Dt PTHREAD_MUTEX 3
Os
Sh NAME
Nm pthread_mutex ,
Nm pthread_mutex_init ,
Nm pthread_mutex_destroy ,
Nm pthread_mutex_lock ,
Nm pthread_mutex_trylock ,
Nm pthread_mutex_unlock ,
Nm pthread_mutex_timedlock ,
Nm pthread_mutex_getprioceiling ,
Nm pthread_mutex_setprioceiling
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 successfully 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 .

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