pthread_rwlock_rdlock man page on DigitalUNIX

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pthread_rwlock_rdlock(3)			      pthread_rwlock_rdlock(3)

       pthread_rwlock_rdlock - Acquires a read-write lock for read access

       #include <pthread.h>

       int pthread_rwlock_rdlock(
	       pthread_rwlock_t *rwlock );

       DECthreads POSIX 1003.1c Library (

       Address of the read-write lock object to acquire for read access.

       This  routine  acquires a read-write lock for read access. If no thread
       already holds the lock for write access and there are no writers	 wait‐
       ing  to	acquire	 the  lock, the lock for read access is granted to the
       calling thread and this routine returns. If a thread already holds  the
       lock for read access, the lock is granted and this routine returns.

       A  thread  can  hold  multiple, concurrent locks for read access on the
       same read-write lock. In a given thread, for each call to this  routine
       that  successfully acquires the same read-write lock for read access, a
       corresponding call to pthread_rwlock_unlock must be issued.

       If some thread already holds the lock for  write	 access,  the  calling
       thread  will  not  acquire  the	read  lock.  If	 the  read lock is not
       acquired, the calling thread blocks until it can acquire the  lock  for
       read  access.  Results  are undefined if the calling thread has already
       acquired a lock for write access on rwlock when this routine is called.

       If the read-write lock object referenced by rwlock is not  initialized,
       the results of calling this routine are undefined.

       If  a thread is interrupted (via a Tru64 UNIX signal or an OpenVMS AST)
       while waiting for a read-write lock for read access, upon  return  from
       the  interrupt routine the thread resumes waiting for the lock as if it
       had not been interrupted.

       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 lock for read access could not be  acquired
       because	the  maximum  number  of read lock acquisitions for rwlock has
       been exceeded.  The current thread already owns the read-write lock for
       writing.	  The  value specified by rwlock does not refer to an initial‐
       ized read-write lock object.


       Functions:     pthread_rwlock_init(3),	   pthread_rwlockattr_init(3),
       pthread_rwlock_tryrdlock(3),		     pthread_rwlock_wrlock(3),

       Manuals: Guide to DECthreads and Programmer's Guide


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