pthread_rwlock_init(3)					     Library Functions Manual					    pthread_rwlock_init(3)

NAME

       pthread_rwlock_init - Initializes a read-write lock object.

LIBRARY

       DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

       #include <pthread.h>

       int   pthread_rwlock_init(
			     pthread_rwlock_t		  *rwlock,
			     const pthread_rwlockattr_t   *attr);

PARAMETERS

       Read-write  lock object to be initialized.  Read-write lock attributes object that defines the characteristics of the read-write lock to be
       initialized.

DESCRIPTION

       This routine initializes a read-write lock object with the attributes specified by the read-write lock attributes object specified in attr.
       A  read-write  lock  is	a synchronization object that serializes access to shared information that needs to be read frequently and written
       only occasionally.  A thread can acquire a read-write lock for shared read access or for exclusive write access.

       Upon successful completion of this routine, the read-write lock is initialized and set to the unlocked state.  If attr is set to NULL,  the
       default	read-write lock attributes are used; the effect is the same as passing the address of a default read-write lock attributes object.
       Once initialized, the lock can be used any number of times without being reinitialized.

       Results of calling this routine are undefined if attr specifies an already initialized read-write lock or if rwlock is used  without  first
       being initialized.

       If this routine returns unsuccessfully, rwlock is not initialized and the contents of rwlock are undefined.

       A  read-write  lock  is	a resource of the process, not part of any particular thread.  A read-write lock is neither destroyed not unlocked
       automatically when any thread exits.  Because read-write locks are shared, they may be allocated in heap or static memory,  but	not  on  a
       stack.

       In  cases where default read-write lock attributes are appropriate, you may use the PTHREAD_RWLOCK_INITIALIZER macro to statically initial-
       ize the lock object without calling this routine.  The effect is equivalent to dynamic initialization by a call to pthread_rwlock_init with
       attr  specified	as  NULL,  except  that no error checks are performed. Statically initialized read-write locks need not be destroyed using
       pthread_rwlock_destroy.

       Use the PTHREAD_RWLOCK_INITIALIZER macro as follows:

       pthread_rwlock_t  rwlock = PTHREAD_RWLOCK_INITIALIZER;

RETURN VALUES

       If an error condition occurs, this routine returns an integer value indicating the type of error.  Possible return values are  as  follows:
       Successful  completion.	 The  system  lacks the necessary resources to initialize the read-write lock.	The implementation has detected an
       attempt to reinitialize the read-write lock (a previously initialized, but not yet destroyed read-write lock object).  The value  specified
       by  attr  is  not a valid attributes block.  Insufficient memory exists to initialize the read-write lock.  The caller does not have privi-
       leges to perform this operation.

ERRORS

       None

RELATED INFORMATION

       Functions: pthread_rwlock_destroy(3)

       Manuals: Guide to DECthreads and Programmer's Guide

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															    pthread_rwlock_init(3)