Path: utzoo!attcan!uunet!wyse!vsi1!ames!pasteur!ucbvax!CITHEX.CALTECH.EDU!carl
From: carl@CITHEX.CALTECH.EDU (Carl J Lydick)
Newsgroups: comp.os.vms
Subject: Re: Event flags and AST
Message-ID: <880724121644.144e@CitHex.Caltech.Edu>
Date: 24 Jul 88 19:21:50 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 28


 > I am stuck with the following problem and I think that I am
 > overlooking something. Part one of my problem was rather easy,
 > problem is really with part 2.  Here it comes:
 > 
 >  1. I needed to "synchronize" the running of several processes. Those
 > processes were SPAWNed from different accounts IN THE SAME GROUP. It
 > was easy enough to create a (temporary) event flag cluster that all
 > these processes shared and make 'em all wait for a specific event
 > flag.  I did this using two very simple programs that I called WAIT
 > and SIGNAL. Essentially when SIGNAL is run, the WAIT program quits
 > running (the event flag is set). 
 >  2. What I need to do is the following:
 >     I need to declare an AST routine in a program. The AST routine
 > should be called when (preferably) an event flag is set. Problem is I
 > could not find a way to let the  program run - apparently you must
 > WAIT for the event flag to be set. I need to let the program run and
 > be interrupted by an event flag being set. 

I don't know how to solve part 2 given that you're using the mechanism of
part 1.  However, depending on how close the synchronization needs to be,
I have a suggestion for another way of doing things:

You could set up mailboxes for each process to be synchronized, and instead
of using event flags, have each process issue a $QIO to its mailbox with
your AST routine as the completion AST routine.  Make sure the AST routine
queues another I/O request to the mailbox.  Then have the process that
would have set the event flag write to each of the mailboxes instead.