From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00
	autolearn=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!gandalf.srv.welterde.de!news.jacob-sparre.dk!franka.jacob-sparre.dk!pnx.dk!.POSTED.rrsoftware.com!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Real tasking problems with Ada.
Date: Fri, 4 Aug 2017 18:16:33 -0500
Organization: JSA Research & Innovation
Message-ID: <om2v8i$dfj$1@franka.jacob-sparre.dk>
References: 
 <9e51f87c-3b54-4d09-b9ca-e3c6a6e8940a@googlegroups.com><olp0qn$ua6$1@franka.jacob-sparre.dk><f9e87130-3f08-43c4-8cc6-9e164a6da954@googlegroups.com>
 <ly4ltpqdrm.fsf@pushface.org>
Injection-Date: Fri, 4 Aug 2017 23:16:34 -0000 (UTC)
Injection-Info: franka.jacob-sparre.dk;
 posting-host="rrsoftware.com:24.196.82.226";
	logging-data="13811"; mail-complaints-to="news@jacob-sparre.dk"
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.7246
Xref: news.eternal-september.org comp.lang.ada:47592
Date: 2017-08-04T18:16:33-05:00
List-Id: <comp.lang.ada>

"Simon Wright" <simon@pushface.org> wrote in message 
news:ly4ltpqdrm.fsf@pushface.org...
> Robert Eachus <rieachus@comcast.net> writes:
>
>> Sigh! Get_Id as defined is heavy only because of the default initial 
>> value:
>>
>>    function Get_CPU
>>       (T   : Ada.Task_Identification.Task_Id :=
>>                  Ada.Task_Identification.Current_Task)
>>            return CPU_Range;
>
> Would it have been reasonable to have used Null_Task_Id to mean 'the
> current task'? (this is a trick used in FreeRTOS at least).

There are rules about when Current_Task is not well-defined (or can raise 
Program_Error, as it is a bounded error to call it in some places). By using 
that here, we don't have to repeat them in every place that might care about 
the current task. If  you used Null_Task_Id as a placeholder, you would have 
to say that Get_CPU is not well-defined (or even when it can raise 
Program_Error).

You'd also lose the null value for representing "no task", which seems to be 
a common requirement for any kind of type.

Thus, that's not the worst idea, but it would be a pain to define and 
possibly would cause issues for anything that needs to represent "no task" 
(such as the default initialization of a data structure).

                                     Randy.