GDSX (Extended General Device Support) Manual

LINE^HANDLER Example, Design

Extended General Device Support (GDSX) Manual—529931-001

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Basic Structure of LINE^HANDLER Code

A LINE^HANDLER task starts when TSCODE calls the LINE^HANDLER procedure.

After any necessary initialization processing, the task runs in a continuous loop,

reading from its $RECEIVE-like queue, never doing a RETURN to TSCODE, as shown

in Figure 7-4. TSCODE uses a nonpreemptive type of task scheduling so USCODE

must voluntarily give up control before TSCODE switches to the next ready task.

At different points you may give up control to TSCODE; for example, when you do a

WAIT^EVENT, your task is suspended, but you never actually exit from the

LINE^HANDLER procedure. A LINE^HANDLER task is stopped by TSCODE when

the GDSX process is stopped (see the last commands in Section 6, LINE^HANDLER

Example, Running and Managing) or when TSCODE receives a message from SCF to

stop a LINE object or stop a LINE task with no openers.

This simple LINE^HANDLER is multithreaded. In the loop, the first thing done is a

^READUPDATE (not a Guardian READUPDATE) on the $RECEIVE-like queue with a

file number in the variable in^queue^file^num, which is passed when this task is

created. This queue receives all messages sent from the DEVICE^HANDLER tasks.

Unlike a ^READUPDATE in a DEVICE^HANDLER task, a ^READUPDATE in a

LINE^HANDLER task does not cause TSCODE to put data into a buffer specified in

the call. Data must be accessed by way of the IOCB provided through a call to

^LISTEN.