pthread_rwlock_rdlock(3)				     Library Functions Manual					  pthread_rwlock_rdlock(3)

NAME

       pthread_rwlock_rdlock - Acquires a read-write lock for read access.

LIBRARY

       DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

       #include <pthread.h>

       int   pthread_rwlock_rdlock(
			     pthread_rwlock_t	      *rwlock);

PARAMETERS

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

DESCRIPTION

       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
       waiting 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.

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 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 ini-
       tialized read-write lock object.

ERRORS

       None

RELATED INFORMATION

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

       Manuals: Guide to DECthreads and Programmer's Guide

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															  pthread_rwlock_rdlock(3)