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From: Brad Moore <brad.moore@shaw.ca>
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Subject: Re: Timeouts in Ada
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Date: 2014-07-25T10:15:29-06:00
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On 2014-07-25 3:11 AM, AdaMagica wrote:
> On Thursday, July 24, 2014 5:37:39 PM UTC+2, Robert A Duff wrote:
>
>> It makes perfect sense to enqueue on multiple entries.
>> In fact, "select call_1 or delay..." enqueues twice (once on
>> the entry call, and once on the timer queue).
>
> That wasn't my point. I just indicated the model.
>
>> Regarding your analogy: There's a supermarket near me where they have
>> just one queue, and the person at the head of the queue takes the first
>> available cash point.  In a sense, they're enqueued on multiple cash
>> points.  ;-)  Like the multi-way call proposed (and rejected) for Ada 9X,
>> they only use one.
>
> That's a very sensible service - I often wish supermarkets here had this model. I find this only in airport counters.
>
> But this is not the same as
>
>>     select
>>       call_1(params);
>>     or
>>       call_2(params);
>>     or
>>       delay 10;
>>     end select;
>
> In your supermarket, there is just one queue, and on the top, you are dispatched to a free cash point, and all of those do the same.
>
> In that multiple select above, the different entries all would/could do different things. In your model: You queue before a gasoline station, a shoemaker, a hardware shop, an accomodation broker; you enter the first free of those.
>

I think Randy's point (or at least one of them) is that the programmer 
can already emulate this easily enough with existing Ada syntax (with a 
bit more effort admittedly) so on top of the other reasons for not 
implementing this, there is less motivation to introduce special syntax 
when the existing syntax already provides a way to achieve the same effect.

eg.

     - Declare two tasks, one whose body calls entry Call1 and the other 
whose body calls Call2.

     - Then instead of the select statement above, write:

    delay 10.0;
    abort T1;
    abort T2;

Brad