On Sat, Sep 17, 2022 at 10:29 AM Ed Jaffe <edja...@phoenixsoftware.com> wrote:
> On 9/17/2022 2:06 AM, Abe Kornelis wrote: > > Starting with reentrant programming seems a pretty tough call. > > Not sure why re-entrant programming should be considered heavy lifting. > Would not any assembler course teach about USING? > For me, the biggest problem in making something reentrant is if I need to use a DCB. There is no way, that I know of, to generate a DCB in a GETMAIN'd area. For ACB, there is a GENACB. Too bad z/OS cannot access non-VSAM datasets using an ACB. From what I've read, z/VSE can in some instances. I now like to write "pure" code. That is, code which does not modify anything in the CSECT. All modifiable data is in GETMAIN'd storage (OK, actually I use STORAGE OBTAIN in HLASM). > > A typical non-reentrant program has a single code/data segment and a > single USING. > > A typical reentrant program has two segments: one for code and one for > data -- each with its own USING. This has been common practice on other > platforms (e.g., Intel) for decades. > > If I were to teach an HLASM course, I can envisage my very first > recommended program organization diagram showing both a code and a data > segment and never once suggesting at any time during the class that code > and data can be (or ever historically were) mixed. Example: > > | R12 -> .---------. R13 -> .---------. > | | | | | > | | Code | | Data | > | | Segment | | Segment | > | | | | | > | '---------' '---------' > > > Baseless should - I guess - pose less of a challenge. > > Agreed. I would not make mention of based branches until the more > advanced portions of the class. > > > -- > Phoenix Software International > Edward E. Jaffe > 831 Parkview Drive North > El Segundo, CA 90245 > https://www.phoenixsoftware.com/ > >
