Re: CICS/400

Hello Jon,

Am 11.08.2023 um 20:19 schrieb Jon Paris <jon.paris@xxxxxxxxxxxxxx>:

For anyone who has ever done S/36 MRT programming CICS is pretty simple.

For those who grew up on the S/38 / AS/400 with the "why should I have to worry about state information?) mentality it is much harder. In some ways it is the same reason that programmers with that background have difficulty getting their heads around web programming. S/36 MRT programmers find the web a breeze!

I know the underlying concept about "conversional transaction" from web server applications (Apache). The client connects, places a request, Apache serves that, feeds back the data and the connection is closed. No state is retained within the web server.
If there is another — related — request to be served, the client is supposed to supply some kind of information so the software being in use "behind" Apache can assign the correct pseudo state (aka: user is already logged in, etc.) Most often, this is handled by web cookies. The client always sends back the cookie and the server has an id or other "state" saved locally to recognize the new request being related to a "session", a series of many requests.

Apache has a set of "workers" (threads or forked processes) where a main dispatcher thread or forked process listening on the TCP port(s) in question for incoming requests and passes those on to already running workers. No need to expensively start and end workers for each request.

While it's indeed easy for me to understand how this works for http, I have not yet enough insight into CICS or 3270 to understand how this works inside CICS and which role 3270 peculiarities play.

But it's fascinating that again IBM has been first with that, before Tim Berners-Lee pushed "start" on the "change the world" button.

:wq! PoC