On 21/06/2022 5:39 am, Charles Mills wrote:
Nay! Rexx passes everything by value, both to internal and to external functions. So
passing <context> will give the assembler code 200 zero bytes to play with but
it will go away on return.
Pass by value doesn't matter. I've done this before and just checked the
code. From 1993, a lifetime ago when I still used REXX. Here's the man
page that get's printed to the terminal if you call it as a TSO command.
It's a KSDS I/O function
which passes back the address of the ACB on open which is then passed
back as a context handle.
The vsamio program can be called as a function from a REXX
EXEC to allow access to VSAM KSDS datasets or invoked from TSO
with no parameters for Help information.
Format;
acb = vsamio(O,ddname) /* Open for read */
acb = vsamio(U,ddname) /* Open for update */
acb = vsamio(X,ddname) /* Open for Alt. Index */
retcod = vsamio(C,acb) /* Close */
record = vsamio(R,acb,key) /* Read with key */
record = vsamio(G,acb,key) /* Read with generic key */
record = vsamio(N,acb,oa_rpl) /* Read next */
record = vsamio(P,acb,oa_rpl) /* Read previous */
retcod = vsamio(W,acb,record) /* Write record */
retcod = vsamio(E,acb,key) /* Erase record */
REXX variables set by function;
oa_rc - VSAM return code (R15 value) or vsamio error code
oa_ec - VSAM error code (R0 value)
oa_rpl - Set following Read Key for Read Next
if oa_rc = 0 then ...... /* Check completion */
And it is unnecessary. I know of no need for persistent storage. Perhaps it is worth persisting the
STIMER MF=L and friends. (I have not yet done detail design. If indicated I will use name/token to
do the persisting. There is also a persistent "user" pointer in the "environment
block" that Rexx maintains and passes, so that is perhaps a better alternative. I have some
detail design work to do.)
The pseudocode is otherwise on target. I would add (watch the line wrap!)
When Left(Res, 1) = 'T'
/* Rexx PARSE command from Res */
/* Re-parametize or whatever is indicated by the command */
Iterate
end
end
/* Close files, clean up and terminate */
The ECB is in MVS-managed storage but it is apparently user-key.
I won't "persist" the STIMER; I will cancel it when I get an F or a P. F should
be infrequent enough that there is little wasted overhead in cancelling the STIMER and
presumably re-starting it. If the caller wants to resume the remaining interval it can
readily enough keep the absolute wakeup time desired and do the necessary arithmetic.
OTOH I guess F could return the remaining interval but that neglects any time spent
processing the F. For P of course the remaining interval is irrelevant.
Whoever mentioned Rexx variables moving around was on target. Rexx's internal storage
management is a black box. It may well move stuff around from time to time. As I say,
everything is passed by value. And there is no C ampersand operator. I know of no way to
get the address of a Rexx variable. Actually, now that I think about it, I have used
IRXEXCOM which returns Rexx variable data "in bulk" to an assembler routine,
but I do not recall the details. It may pass the actual address, not a copy of the value
-- I don't recall.
Charles
-----Original Message-----
From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] On Behalf
Of David Crayford
Sent: Monday, June 20, 2022 11:10 AM
To:IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: Some UNIX file usage questions
I think I understand what Charles is doing.
context = copies('00'x,200) <-- state for HLASM program
wait_time = 30
do forever
res = console(context, wait_time)
select
when res = 'T' then iterate
when res = 'P' then leave
otherwise ...
end
end
On 21/06/2022 1:58 am, Paul Gilmartin wrote:
I'll correct my earlier misstatement. You did not say you were the client;
merely "-n-house".
On Mon, 20 Jun 2022 10:41:25 -0700, Charles Mills wrote:
The ECB is not in the Rexx. It is in MVS-owned storage IIRC.
I believe ECBs routinely occupy user-owned storage.
-----Original Message-----
...
... Well, the actual parameter passed by the Rexx is continuously accessible to
the Assembler. It is of course possible to access any Rexx variable from
assembler, but I see no need. If I understand your question, the answer is No.
I took "continuously accessible" to mean accessible by concurrent tasks even
after
the Assembler returns to Rexx.
That depends on the AFAIK undocumented behavior of Rexx storage
management. What happens if Rexx compacts variable storage, thereby
moving an ECB? Rexx spurns concurrency.
"ECB" for example. The Devil's advocate was envisioning using the parameter
passed by Rexx as working storage. Which is OK until returning to Rexx.
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