pthread_rwlock_wrlock(3)				     Library Functions Manual					  pthread_rwlock_wrlock(3)

NAME

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

LIBRARY

       DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

       #include <pthread.h>

       int   pthread_rwlock_wrlock(
			     pthread_rwlock_t	      *rwlock);

PARAMETERS

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

DESCRIPTION

       This  routine attempts to acquire a read-write lock for write access.  If any thread already has acquired the lock for write access or read
       access, the lock is not granted and the calling thread blocks until it can acquire the lock. A thread can hold  only  one  lock	for  write
       access on a read-write lock.

       Results	are  undefined	if  the  calling  thread  holds the read-write lock (whether for read or write access) at the time 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 write  access,  upon  return
       from the interrupt routine the thread resumes waiting for the lock as if it had not been interrupted.

       Realtime applications can encounter priority inversion when using read-write locks. The problem occurs when a high-priority thread acquires
       a read-write lock that is about to be unlocked (that is, posted) by a low-priority thread, but the low-priority thread is  preempted  by  a
       medium-priority	thread.  This scenario leads to priority inversion in that a high-priority thread is blocked by lower-priority threads for
       an unlimited period of time.  During system design, realtime programmers must take into account the possibility of priority  inversion  and
       can  deal with it in a number of ways, such as by having critical sections that are guarded by read-write locks execute at a high priority,
       so that a thread cannot be preempted while executing in its critical section.

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 current thread already owns the read-write lock for write or read access.	The value specified by rwlock does
       not refer to an initialized read-write lock object.

ERRORS

       None

RELATED INFORMATION

       Functions:      pthread_rwlock_init(3),	    pthread_rwlockattr_init(3),       pthread_rwlock_rdlock(3),       pthread_rwlock_trywrlock(3),
       pthread_rwlock_unlock(3)

       Manuals: Guide to DECthreads and Programmer's Guide

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															  pthread_rwlock_wrlock(3)