TRUE 
on success and FALSE on failure, by default generating an 
exception. The flags argument is a bitwise disjunction of 
these flags:
SIO_INPUTSIO_OUTPUTSIO_INPUT for details. 
If neither SIO_OUTPUT nor SIO_INPUT is given t 
may not be a pair.SIO_TRYLOCKFALSE if the stream cannot be locked immediately. No 
error is generated.SIO_NOERRORThe returned stream is owned by the calling thread using PL_acquire_stream().