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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Finalization of library level tasks
Date: Thu, 26 Apr 2018 18:43:04 +0200
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Xref: reader02.eternal-september.org comp.lang.ada:51729
Date: 2018-04-26T18:43:04+02:00
List-Id: <comp.lang.ada>

On 2018-04-26 18:22, Jeffrey R. Carter wrote:
> On 04/26/2018 01:54 AM, Randy Brukardt wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>>>
>>> The only place RM explains 'Callable is in ARM C.7.1:riddle:
>>
>> Interesting. It should be declared somewhere. Anyway, the rule is that
>> T'Callable = True unless the task is completed. See 9.3 for the 
>> definition
>> of completed.
> 
> 'Callable and the concept of "callable" are defined at ARM 9.9(2): 
> "T'Callable Yields the value True when the task denoted by T is 
> callable, and False otherwise; a task is callable unless it is completed 
> or abnormal."

Literally it means "can be called". In

task body T is
begin
    select
       accept X;
    or terminate;
    end select;
end T;

X cannot be called when the master awaits termination of T. Thus 
*logically* T is not callable when terminate will be selected.

Surely there could be another attribute with a different name, or a 
predefined entry to be accepted when the master is waiting. Or both.

Among with finalization deadlock another problem of terminate 
alternative is that there is not rendezvous. Surely programmers wish do 
be able to do explicit cleanup on termination without misusing 
controlled objects:

    select
       ...
    or terminate do
       ... -- Complete task
       end terminate;
    end select;

[ Yes, we want to be able to requeue terminate and to make entry calls 
from there. ]

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de