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NAME    [Toc]    [Back]

       pthread_rwlock_rdlock  -  Acquires  a  read-write lock for
       read access

SYNOPSIS    [Toc]    [Back]

       #include <pthread.h>

       int pthread_rwlock_rdlock(
               pthread_rwlock_t *rwlock );

LIBRARY    [Toc]    [Back]

       DECthreads POSIX 1003.1c Library (libpthread.so)

PARAMETERS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       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    [Toc]    [Back]

       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 readwrite
 lock for writing.  The  value  specified  by  rwlock
       does not refer to an initialized read-write lock object.

ERRORS    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

       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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