pthread_mutexattr_settype(3P)			 pthread_mutexattr_settype(3P)

NAME    [Toc]    [Back]

     pthread_mutexattr_settype,	pthread_mutexattr_gettype - set/get a mutex
     attribute object's	type

C SYNOPSIS    [Toc]    [Back]

     #include <pthread.h>

     int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type);

     int pthread_mutexattr_gettype(pthread_mutexattr_t *attr, int *type);

DESCRIPTION    [Toc]    [Back]

     These functions manipulate	a mutex	attribute object referenced by attr
     which has been previously created by pthread_mutexattr_init().

     The function pthread_mutexattr_settype() defines the type of mutex.  The
     type value	may be one of PTHREAD_MUTEX_NORMAL, PTHREAD_MUTEX_ERRORCHECK,
     PTHREAD_MUTEX_RECURSIVE, PTHREAD_MUTEX_SPINBLOCK_NP, or
     PTHREAD_MUTEX_DEFAULT.

     The function pthread_mutexattr_gettype() stores into the memory
     referenced	by type	the mutex type associated with the named mutex
     attribute object.	The default type is PTHREAD_MUTEX_DEFAULT.

     A mutex with a type attribute of PTHREAD_MUTEX_DEFAULT or
     PTHREAD_MUTEX_NORMAL works	as a simple mutual exclusion lock with no
     error checking.  A	thread attempting to relock a mutex of this type will
     deadlock.

     A mutex with a type attribute of PTHREAD_MUTEX_ERRORCHECK is a simple
     mutual exclusion lock with	error checking.	 A thread attempting to	relock
     a mutex of	this type will return an error.	 A thread attempting to	unlock
     a mutex that another thread has locked will return	an error.  A thread
     attempting	to unlock a mutex that has not been locked will	return an
     error.

     A mutex with a type attribute of PTHREAD_MUTEX_RECURSIVE is a simple
     mutual exclusion lock with	error checking that also allows	a single
     thread to recursively lock	the mutex.  In this case there must be a
     matching number of	unlocks	by the thread before the mutex can be
     released.	A thread attempting to unlock a	mutex that another thread has
     locked will return	an error.  A thread attempting to unlock a mutex that
     has not been locked will return an	error.

     A mutex with a type attribute of PTHREAD_MUTEX_SPINBLOCK_NP is a mutual
     exclusion lock which spins	for a configurable amount of time then blocks.
     The mutex continues to spin then block until the lock is obtained.	 An
     environment variable is provided to tune this type	of mutex. The
     environment variable MTX_SPINS is used to control the number of times the
     lock is tried before blocking.  The default value is set to 600. When a
     thread unlocks a spinblock	mutex, it clears the lock word then issues an
     unblock if	there are waiters for the lock.	Once a blocked thread is



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pthread_mutexattr_settype(3P)			 pthread_mutexattr_settype(3P)



     awakened, it still	needs to try to	acquire	the lock. Thread priority is
     therefore not preserved with this type of mutex. Also,
     pthread_mutexattr_setprioceiling()	and pthread_mutexattr_setprotocol()
     cannot be used with this type of mutex.

DIAGNOSTICS    [Toc]    [Back]

     The mutex attribute type functions	return zero on success;	otherwise, an
     error number is returned:

     [EINVAL]	    The	value specified	by type	is invalid.

     [EINVAL]	    The	value specified	by type	is PTHREAD_MUTEX_SPINBLOCK_NP
		    and	pthread_mutexattr_setprioceiling() or
		    pthread_mutexattr_setprotocol() has	already	been called
		    for	the mutex.

SEE ALSO    [Toc]    [Back]

     pthread_mutex_lock(3P), pthread_mutexattr_init(3P),
     pthread_mutexattr_setprotocol(3P).


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