pthread_rwlock_init(3T) 												   pthread_rwlock_init(3T)

NAME

       pthread_rwlock_init(), pthread_rwlock_destroy() - initialize or destroy a read-write lock

SYNOPSIS

PARAMETERS

	      rwlock	Pointer to the read-write lock to be initialized or destroyed.

	      attr	Pointer  to  the  attributes  object  that  defines  the characteristics of the read-write lock to be initialized.  If the
			pointer is NULL, default attributes are used.

DESCRIPTION

       initializes the read-write lock referenced by rwlock with the attributes attr.  If attr is NULL, the default read-write lock attributes are
       used.   Upon  successful  initialization,  the  state of the read-write lock becomes initialized and unlocked.  Attempting to initialize an
       already initialized read-write lock object results in undefined behavior.

       The macro can be used to initialize read-write locks which are statically allocated.  The effect is equivalent to dynamic initialization by
       a  call	to  with the attr parameter specified as NULL, except that no error checks are performed.  The read-write lock will be initialized
       with default attributes.

       If the process-shared attribute in the read-write lock attributes object referenced by attr is defined as the read-write lock must be allo-
       cated  such  that  the  processes sharing the read-write lock has access to it.	This may be done through the memory-mapping functions (see
       mmap(2)) or shared memory functions (see shmget(2)).

       destroys the read-write referenced by rwlock.  This function may set rwlock to an invalid value.  The  destroyed  read-write  lock  can	be
       reinitialized using the function If the read-write lock is referenced after destruction in any read-write lock call, the resulting behavior
       is undefined.

       A read-write lock should be destroyed only when no threads are currently using it.  Destroying a read-write lock which is currently in  use
       results in undefined behavior.

RETURN VALUE

       Upon successful completion, and returns zero.  Otherwise, an error number is returned to indicate the error (the variable is not set).

ERRORS

       If any of the following occur, the function returns the corresponding error number:

	      The necessary resources (other than memory) to initialize
			     rwlock are not available.

	      rwlock	     is an already initialized read-write lock.  However, getting for reinitializing the rwlock cannot be expected all the
			     time since the behavior of reinitializing the rwlock is undefined.

	      The value specified by
			     rwlock or attr is invalid.

	      There is insufficient memory available in which to initialize the
			     read-write lock rwlock.

	      The caller does not have the privilege to perform the operation.

       If any of the following occur, the function returns the corresponding error number:

	      rwlock	     is currently locked or being used by other threads.

	      The value specified by
			     rwlock is invalid.

WARNINGS

       The space for the read-write lock must to be allocated before calling Undefined behavior may result if the process-shared attribute of attr
       is and the space allocated for the read-write lock is not accessible to cooperating threads.

AUTHOR

       and were developed by X/Open.

SEE ALSO

       pthread_rwlock_rdlock(3T),	   pthread_rwlock_tryrdlock(3T),	  pthread_rwlock_trywrlock(3T), 	pthread_rwlock_unlock(3T),
       pthread_rwlock_wrlock(3T).

STANDARDS CONFORMANCE

								  Pthread Library					   pthread_rwlock_init(3T)