At  4:44 PM 2/2/96 +0000, Tom Emerson wrote:
>THEN I started looking through the intrinsics, interprocess communications,
>etc. handbooks on the latest CD rom and found EXACTLY what I was looking for
> -- an "interrupt" service routine!  You can use FCONTROL(message-file, 48,
>interrupt-handler-address) to specify a routine that handles incoming
>messages when the processor is "busy" with another part of the program (such
>as waiting for a terminal or socket read to complete)
 
There are some gotchas with this:
 
1. Most system code can't be interrupted. The exceptions are IOWAIT and
PAUSE. So you'll still have to do nowait I/O on the terminal in order to
get what you want. The soft interrupt will not interrupt an FREAD.
 
2. I'm dealing right now with some bizarre happenings in soft interrupts.
Specifically, if you're using a generic IOWAIT as well as soft interrupts,
you sometimes get an IOWAIT completion on the file for which you have the
soft interrupt enabled. After that, you get a soft interrupt, but the
IOWAIT in the soft interrupt handler returns "No no-wait I/O pending"
because the I/O has already been completed by the IOWAIT. The response
center is looking for a solution; I'm not hopeful since the engineer
assigned to the call did not understand the function of an FCONTROL 48 -- I
had to explain it to him.
 
3. If your soft interrupt routine might be called from privileged code, you
must enable soft interrupts from privileged mode.
 
-- Bruce
 
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