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Date: Wed, 21 Jan 2015 08:53:46 -0800 (PST)
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Subject: Re: How to: communication between multiple tasks using protected
 objects - with no polling?
From: Esa Riihonen <esa.riihonen.er@gmail.com>
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Xref: number.nntp.giganews.com comp.lang.ada:191975
Date: 2015-01-21T08:53:46-08:00
List-Id: <comp.lang.ada>

keskiviikko 21. tammikuuta 2015 2.19.43 UTC+2 Hubert kirjoitti:

... snip ...

> So my solution was to have one protected object that serves as a form of=
=20
> event buffer.
>=20
> Any section of my code that needs to communicate with the task, writes=20
> an event into the PO. The task then waits for an event in the PO. the PO=
=20
> provides these events through an entry with a  barrier that is something=
=20
> like "WHEN LENGTH( Event_Queue) > 0".

The thing is that in this special case I have in mind my 'writers' are just=
 reporting their status once in a while and have more important things to d=
o - so I don't want them blocked. If I have just one PO for the 'reader' th=
en the 'writers' might block each other and be unnecessry blocked while the=
 'reader' is going through the messages of the other 'writers'. Thus I trie=
d to build the system with one separete PO for each writer task.=20
=20
I guess that in practice the associated blocking delays are not a concern i=
n this case. But as I'm using this as an excercise for Ada I'm also concern=
ed about this 'in principle' ;)

> You can then also use a timed select statement like so:
>=20
> SELECT
>    Wait_For_Event( PO );
> OR
>    Delay 1.0;
> END SELECT
>=20
> which will time out after 1 second and allow your task to do something=20
> else before entering the select statement again in a loop. For instance=
=20
> you could check for a task entry that commands your task to halt and=20
> exit, if you want to delete the task or shut down the program

That is a good point - I probably will end up implementing the logic along =
these lines.=20

Thanks.

... snip ...