pthread_rwlock_tryrdlock(3)				     Library Functions Manual				       pthread_rwlock_tryrdlock(3)

NAME

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

LIBRARY

       DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

       #include <pthread.h>

       int   pthread_rwlock_tryrdlock(
			     pthread_rwlock_t	      *rwlock);

PARAMETERS

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

DESCRIPTION

       This routine attempts to acquire a read-write lock for read access, but does not wait for the lock if it not immediately available.

       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  rou-
       tine returns.

       If  some  thread  already holds the lock for write access, the calling thread will not acquire the read lock.  Results are undefined if the
       calling thread has already acquired a lock for write access on rwlock when this routine is called.

       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 the read-write lock object referenced by rwlock is not initialized, the results of calling this routine are undefined.

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 read access because another thread  already  acquired  it	for  write
       access  or  is blocked and waiting for it for write 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 writing.  The lock for read access could not be acquired because the maxi-
       mum 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_rdlock(3), pthread_rwlock_wrlock(3), pthread_rwlock_unlock(3)

       Manuals: Guide to DECthreads and Programmer's Guide

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														       pthread_rwlock_tryrdlock(3)