Thanks Dieter, Tim and Rob
Informative, amusing and insightful - I'll carefully read and see how I can apply to my project.
-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of D*B
Sent: Thursday, November 20, 2014 2:03 AM
To: Midrange Systems Technical Discussion
Subject: RE: Is job x running
... for a data warehouse load process, we've needed multiple conditions, what could run together. We wrote a SRVPGM (not too complcated) with following procedures
getMutex(name, wait){
if syncobj with name not exists create
try to lock the syncobj with specified wait if not possible in time throw exception (send escape message via QMHSNDPM store locks in some array }
releaseAll(){
free all locks
}
If you need more than one lock (we needed this for some sophisticated
schedules) be carefull with deadlocks. It's easier to avoid deadlocks, than handling. simply define an order to get more than one: they have to be sorted by alphabet. e.g. if someone has a lock to 'HUGO', he could get 'MARTHA'. If he tries to get 'ADAM' throw an exception.
We used a special lockfile and inserted a record with name as one keyfield and held the lock using commitment controll to release all we specified commit (so this must run in a named ACTGRP only used for this SRVPGM.
Advantage of this is, that you could see the sequence of aquired locks in journal (if you use a FlipFlop mechanism := an int column created with contents 1 multiplied by -1 for eych update).
If you need more flexibility, to release only a single lock, still holding others (releaseMutex(name)) , some lightweight syncobjects are better.
The QUSLOBJ and the write some info to a DTAARA/FILE I wouldn't recommend.
The first is not correct, if more than one is trying to run at the same time, maybe none of them will win, worst case blocking each other. The second is incorrect too, if a job dies you would have to do some manual repair before it could run next time.
Dieter
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