Dennis, here's the IBM book on the issue. Not terribly helpful but it gives you the basic idea.

The idea is that if the entry on the data queue is *DSPF, then READ the display file, otherwise do whatever the entry says (which in this business case would be to upadte the data and WRITE the display file).


Great to hear it's possible, Jack. Care to elaborate on _how_ one would
post updates to the 5250 screen (barring status messages, which are too
limited to satisfy the need) without flicker, flash, or disruption to user
input? That is a challenge for which I have never seen a solution with the
(naturally-blocking) 5250 display.

Dennis Lovelady
"Never lend books, for no one ever returns them. The only books I have in
my library are those that other folks have lent me."
-- Anatole France

Not only possible with RPG and 5250- it's been possible since IBM
enabled display files to post status changes to data queues. FWIW, I
believe that feature was introduced on the System 38 from the research
I did supporting an such an application 12 years ago. Said app was at
least 10 years old at that time.

Was an undocumented maintenance nightmare until I used object auditing
to trace through the event chains, but I came to appreciate it as one
of the most elegant designs I've seen implemented on the platform.

... for this kind of application, you would need 2 parts:
- a runtime supporting registration of listeners (windows, xwindows
something comparable as Javascript based for a browser interface)
- a programming language supporting Multithreading (remark: rpg with
is not possible)
most of this is done with Java, C# and C++

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