Basic EOV is transparent, but if you have the "unlike attributes" bit set, things happen that you must be aware of.
-- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Discussion List [[email protected]] on behalf of Michael Stein [[email protected]] Sent: Saturday, March 20, 2021 11:51 AM To: [email protected] Subject: Re: Overlapped I/O completion On Fri, Mar 19, 2021 at 08:08:28PM -0500, Paul Gilmartin wrote: > On Fri, 19 Mar 2021 21:50:57 +0000, Seymour J Metz wrote: > > >> Is there any reason to do a WAIT before the CHECK? > >EOV processing. Normally a CHECK just waits on the ECB and does a minimal amount of processing. If there is some sort of error, end of file, or EOV case then it can take longer. EOV processing can involve an internal CLOSE/OPEN say for example the next dataste in a concatenation. This take much more time than just checking an ECB for 7F (I/O complete normally). If you had lots of work which was independent you could do other work after the READ(s) and before any WAIT or CHECK. Then after doing some other work, you could test the ECB in the DECB to see if was done. If it's done you could issue CHECK knowing that it usually won't delay you. And process that block and then issue another READ. If you ran out of work to do and none of your pending READs had completed You could (for example) issue a WAIT with a list of ECBs which included your pending READs along with other unrelated work which is pending. When you wake you check the ECBs and do more processing related to whatever got done... By doing this you can get other processing done while the READs are running. You still need to issue CHECK for each READ but you avoid the explicit WAIT inside of CHECK but not the error processing or EOV/EOF processing. > It was long ago and I no longer have the code. IIRC, I coded a CHECK, > but never a WAIT. It was specialized code, and I may not have accounted > for EOV. EOV would be transparent, just a delay. > What ill at EOV befalls a programmer who codes a CHECK but not a WAIT. Nothing. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
