GDSX Manual

DEVICE^HANDLER Example, Design
Extended General Device Support (GDSX) Manual–134303
5-7
USKELEX Example Code
At different points the task may give up control to TSCODE, for example, when the task
does a ^AWAITIO following a ^WRITEREAD, the task is suspended, but there is no
actual exit from the DEVICE^HANDLER procedure. A task is stopped by TSCODE if
TSCODE receives a message from SCF to stop the SU, if TSCODE receives a message
from a requester thread to close the terminal to which it is mapped, or if the task stops
itself through a call to STOP^TASK.
This simple example program behaves like a single-threaded process (although
multithreaded operation is possible within a DEVICE^HANDLER task). In the loop,
the first thing done is a ^READUPDATE (not a Guardian READUPDATE) on pseudo-
$RECEIVE, which always has a file number of 0. Then there is logic to determine what
kind of request has been picked up from pseudo-$RECEIVE. (The types of requests
involved, while typical of a passthrough program, are example specific; other
applications might have more message-oriented requests.)
Datastream conversion is done at PROCESS REQUEST DATA in Figure 5-3, before
issuing a ^WRITE or ^WRITEREAD to the IOP. After a ^WRITEREAD or ^READ
there will be data coming back from the IOP. Although this example does not perform
incoming datastream translation, such processing could be included at the place in the
figure marked PROCESS REPLY DATA. CONTROL and SETMODE messages
picked up on the pseudo-$RECEIVE are simply passed on to the IOP.
Although every one of the I/O procedures used is inherently a nowait operation, from the
task’s point of view, the DEVICE^HANDLER uses waited I/O, because each of the I/O
calls is followed immediately with a ^AWAITIO, effectively making it a waited
operation.
USKELEX Example Code
This subsection examines the USKELEX source code. A complete listing is shown in
Appendix B. Example 5-1 shows the global declarations, which are typical for a user
source file. Global data within the common^data block can be referenced and updated
by both TSCODE and USCODE, while global data within the user^private data block
can be referenced and updated only by USCODE tasks.