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pthread_mutex_lock(3P)					pthread_mutex_lock(3P)

NAME    [Toc]    [Back]

     pthread_mutex_init, pthread_mutex_lock, pthread_mutex_trylock,
     pthread_mutex_unlock, pthread_mutex_destroy - mutual exclusion locks

C SYNOPSIS    [Toc]    [Back]

     #include <pthread.h>

     int pthread_mutex_init(pthread_mutex_t *mutex,
	  const	pthread_mutexattr_t *attr);

     int pthread_mutex_lock(pthread_mutex_t *mutex);

     int pthread_mutex_trylock(pthread_mutex_t *mutex);

     int pthread_mutex_unlock(pthread_mutex_t *mutex);

     int pthread_mutex_destroy(pthread_mutex_t *mutex);

DESCRIPTION    [Toc]    [Back]

     Mutual exclusion locks (mutexes) are used to serialize the	execution of
     threads through critical sections of code which access shared data.  A
     successful	call for a mutex lock via pthread_mutex_lock() or
     pthread_mutex_trylock() will cause	another	thread that tries to acquire
     the same mutex via	pthread_mutex_lock() to	wait until the owning thread
     calls pthread_mutex_unlock().  The	wait could mean	that the thread	is
     blocked immediately or if the mutex type is PTHREAD_MUTEX_SPINBLOCK_NP,
     the thread	will spin first	then block.

   Initialize    [Toc]    [Back]
     Mutexes may be initialized	either dynamically, by calling
     pthread_mutex_init(), or statically, via the macro

     The personality of	the mutex is determined	by the attribute structure
     attr passed with the call to pthread_mutex_init().	 These attributes are
     set by calls to pthread_mutexattr_init() and the various pthread mutex
     attribute functions.  If attr is null (or the mutex is statically
     initialized), the default attributes are used.

   Lock	and Unlock
     A mutex lock protects shared data from simultaneous access	by multiple
     threads.  A thread	that calls pthread_mutex_lock()	will wait until	it can
     gain exclusive ownership of a mutex, and retains ownership	until it calls
     pthread_mutex_unlock().  Only the thread that locked a mutex should
     unlock it.	 When the mutex	is unlocked, if	there are any threads waiting
     for the mutex the relative	priorities of the blocked threads and the
     scheduling	policy determines which	thread next acquires the mutex.	 When
     a thread unlocks a	PTHREAD_MUTEX_SPINBLOCK_NP type	of mutex, it issues an
     unblock if	there are waiters for the lock.	However, once a	blocked	thread
     is	awakened, it still needs to try	to acquire the lock. Thread priority
     is	therefore not preserved	with this type of mutex.

									Page 1

pthread_mutex_lock(3P)					pthread_mutex_lock(3P)

     If	a thread waiting for a mutex receives a	signal,	upon return from the
     signal handler, the thread	resumes	waiting	for the	mutex as if there was
     no	interrupt.

   Destroy    [Toc]    [Back]
     The routine pthread_mutex_destroy() uninitializes the mutex object
     referenced	by mutex.

DIAGNOSTICS    [Toc]    [Back]

     All of the	mutex functions	return zero if successful; otherwise, an error
     number is returned.

     pthread_mutex_lock() can return the following errors:

     [EDEADLK]	    The	current	thread already owns the	mutex. The mutex type

     [EINVAL]	    The	mutex was initialized as type PTHREAD_PRIO_PROTECT and
		    the	calling	thread's priority was greater than the mutex's
		    priority ceiling.

     pthread_mutex_trylock() can return	the following errors:

     [EBUSY]	    The	mutex is currently held	by another thread.

     [EINVAL]	    The	mutex was initialized as type PTHREAD_PRIO_PROTECT and
		    the	calling	thread's priority was greater than the mutex's
		    priority ceiling.

     pthread_mutex_unlock() can	return the following error:

     [EPERM]	    The	current	thread does not	own the	mutex.	The mutex type

     pthread_mutex_destroy() can return	the following error:

     [EBUSY]	    The	mutex is currently held	by any thread.

SEE ALSO    [Toc]    [Back]

     pthread_cond_init(3P), pthread_mutexattr_init(3P),
     pthread_mutexattr_setprioceiling(3P), pthread_mutexattr_setprotocol(3P),
     pthread_mutexattr_setpshared(3P), pthread_mutexattr_settype(3P).

									PPPPaaaaggggeeee 2222
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