Index for Section 3

Alphabetical listing for P

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

DESCRIPTION
  This routine acquires a read-write lock for read access.  If a thread
  already holds the lock for read access, the lock is granted and this
  routine returns.  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.

  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
  corrresponding 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
  signal handler 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:

  0	    Successful completion.

  [EINVAL]  The value specified by rwlock does not refer to an initialized
	    read-write lock object.

  [EDEADLCK]
	    The current thread already owns the read-write lock for writing.

  [EAGAIN]  The lock for read access could not be acquired because the
	    maximum number of read lock acquisitions for rwlock has been
	    exceeded.

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