pthread_rwlock_tryrdlock man page on HP-UX

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pthread_rwlock_rdlock(3T)			     pthread_rwlock_rdlock(3T)

NAME
       pthread_rwlock_rdlock(),	 pthread_rwlock_tryrdlock()  - lock or attempt
       to lock a read-write lock for reading

SYNOPSIS
PARAMETERS
	      rwlock	Pointer to the read-write lock to be locked for	 read‐
			ing.

DESCRIPTION
       The  function  applies a read lock to the read-write lock object refer‐
       enced by rwlock.	 The calling thread shall acquire a  read  lock	 if  a
       writer  does  not hold the lock and there are no writers blocked on the
       lock.  It is unspecified whether the calling thread acquires  the  lock
       when  a writer does not hold the lock and there are writers waiting for
       the lock.  If a writer holds the lock, the  calling  thread  shall  not
       acquire	the  read lock.	 If the read lock is not acquired, the calling
       thread blocks (that is, it does not return from the call) until it  can
       acquire	the  lock.   Results  are undefined if the calling thread cur‐
       rently owns a write lock on rwlock.

       Implementations shall be allowed to favor writers over readers to avoid
       writer starvation.

       A  thread  may  hold multiple concurrent locks on rwlock (that is, suc‐
       cessfully call the function n times). If so, the	 thread	 must  perform
       the matching unlocks (that is, it must call the function n times).

       The  function applies a read lock as in the function with the exception
       that the function fails if any thread holds a write lock on  rwlock  or
       there are writers blocked on rwlock.

       Results	are  undefined	if  any	 of these functions are called with an
       uninitialized read-write lock.

       If a signal is delivered to a thread waiting  for  a  read-write	 lock,
       upon  return  from  the signal handler, the thread shall resume waiting
       for the read-write lock as if it was not interrupted.

RETURN VALUE
       Upon successful completion, and return zero. Otherwise, an error number
       is returned to indicate the error (the variable is not set).

ERRORS
       If  any	of the following occur, the function returns the corresponding
       error number:

	      [EBUSY]	     The read-write lock rwlock could not be  acquired
			     for  reading  because  a writer holds the lock or
			     was blocked on it.

       For each of the following conditions, if the condition is detected, the
       and functions return the corresponding error number:

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

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

	      [EAGAIN]	     The  read	lock could not be acquired because the
			     maximum number of read locks for rwlock has  been
			     exceeded. This error is not detected on HP-UX.

AUTHOR
       and were developed by X/Open.

SEE ALSO
       pthread_rwlock_init(3T),			   pthread_rwlock_destroy(3T),
       pthread_rwlock_trywrlock(3T),		    pthread_rwlock_wrlock(3T),
       pthread_rwlock_unlock(3T).

STANDARDS CONFORMANCE
				Pthread Library	     pthread_rwlock_rdlock(3T)
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