(PHP 5)
streamWrapper::stream_lock — Advisory file locking
$operation
   )
   This method is called in response to flock(), when
   file_put_contents() (when flags
   contains LOCK_EX),
   stream_set_blocking() and when closing the stream
   (LOCK_UN).
  
operation
       operation is one of the following:
       
LOCK_SH to acquire a shared lock (reader).
         
        LOCK_EX to acquire an exclusive lock (writer).
         
        LOCK_UN to release a lock (shared or exclusive).
         
        LOCK_NB if you don't want
          flock() to block while locking.
          (not supported on Windows)
         
        
   Returns TRUE on success or FALSE on failure.
  
   Emits E_WARNING if call to this method fails (i.e. not implemented).