NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

       #include <pthread.h>

       int pthread_rwlock_tryrdlock(
               pthread_rwlock_t *rwlock );

LIBRARY    [Toc]    [Back]

       DECthreads POSIX 1003.1c Library (libpthread.so)

PARAMETERS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       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 routine
       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 corresponding 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    [Toc]    [Back]

       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 maximum
       number of read  lock  acquisitions  for  rwlock  has  been
       exceeded.

ERRORS    [Toc]    [Back]

       None

SEE ALSO    [Toc]    [Back]

       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



                                      pthread_rwlock_tryrdlock(3)