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Newsgroups: comp.lang.ada
Subject: Re: process blocking
References: <41400af9$1@dnews.tpgi.com.au>
 <mailman.6.1094729905.390.comp.lang.ada@ada-france.org>
 <41404385$1@dnews.tpgi.com.au>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: Thu, 09 Sep 2004 20:09:12 +0200
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Date: 2004-09-09T20:11:08+02:00
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"P Hull" writes:
> Oh i was not looking for a static solution. pMain is visible to all
> tasks p1..pn. The first task (i.e. one of p1..pn based upon some
> timing mechanism) will rendezvous with pMain and seizes pMain. And
> once pi has finished whatever it wants to do with pMain, some other
> task within p1..pn will then next rendezvous with pMain and seize
> it, and once finished .. etc etc
>
> I know this should be simple to implement. Thanks for any help

Why does pMain have to be a task?  Could it not be a protected object
instead?  Then, the task pi would call a procedure or entry in the
protected object.  While that procedure or entry is executing, other
tasks that also want to execute a procedure or entry in pMain must
wait.

Here is an example:

protected pMain is
   procedure Seize_And_Do_Whatever;
private
   Protected_Data : Integer;
end pMain;

protected body pMain is
   procedure Seize_And_Do_Whatever is
   begin
      Protected_Data := 42;
   end Seize_And_Do_Whatever;
end pMain;

Now, any task pi can call pMain.Seize_And_Do_Whatever.  The processing
takes place in the task pi; pi is not blocked.  If another task, pj,
wants to call pMain.Seize_And_Do_Whatever, it waits.

See the reference manual section 9.4 for more details.

[1] http://www.adaic.org/standards/ada95.html
[2] http://www.adaic.org/standards/95lrm/html/RM-9-4.html

-- 
Ludovic Brenta.