pthread_rwlock_trywrlock(3)				     Library Functions Manual				       pthread_rwlock_trywrlock(3)

NAME

       pthread_rwlock_trywrlock - Attempts to acquire a read-write lock for write access without waiting.

LIBRARY

       DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

       #include <pthread.h>

       int   pthread_rwlock_trywrlock(
			     pthread_rwlock_t	      *rwlock);

PARAMETERS

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

DESCRIPTION

       This routine attempts to acquire the read-write lock referenced by rwlock for write access. If any thread already holds that lock for write
       access or read access, this routine fails and returns [EBUSY] and the calling thread does not wait for the lock to become available.

       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.

       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  read-write lock could not be acquired for write access because it was already locked for write access or for
       read access.  The value specified by rwlock does not refer to an initialized read-write lock object.  The current thread already  owns  the
       read-write lock for write or read access.

ERRORS

       None

RELATED INFORMATION

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

       Manuals: Guide to DECthreads and Programmer's Guide

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														       pthread_rwlock_trywrlock(3)