Re: Composing tasks and protected objects

[Jeffrey Carter <spam@spam.com>]

Florian Weimer wrote:
> Suppose I want to write a selective accept which reads messages from a
> queue, and also support a special entry call to reload the
> configuration.

You need all calls to go the same way. Right now you're trying to do 
something like

+----------+          +----------+          +----------+
|          |          |          |          |          |
|     Q    |<--Get----|  Server  |<--Shut---|     ?    |
|          |          |          |   Down   |          |
|          |          |          |<--Reload-|          |
|          |          |          |          |          |
+----------+          +----------+          +----------+

where arrows indicate direction of call. This won't work, but it will 
work if you can turn that call to Get around. For this, you need a 
forwarder between the Queue and Server:

+----------+       +----------+       +----------+       +----------+
|          |       |          |       |          |       |          |
|     Q    |<-Get--| Forwarder|--Msg->|  Server  |<-Etc--|     ?    |
|          |       |          |       |          |       |          |
+----------+       +----------+       +----------+       +----------+

Now your task can look like

select
    accept Msg (Message : in ...) do
       Current_Message := Message;
    end Msg;

    Process_Message (Current_Message);
or
    ... -- as in your example
end select;

The only difficulty is terminating the Forwarder.

-- 
Jeff Carter
"Go and boil your bottoms."
Monty Python & the Holy Grail
01