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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: is there a version of unix written in Ada
Date: Sat, 3 Oct 2020 10:44:59 +0300
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On 2020-10-03 9:42, Dmitry A. Kazakov wrote:
> On 03/10/2020 05:09, Randy Brukardt wrote:
>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
>> news:rl6its$10h7$1@gioia.aioe.org...
> 
>>>> [If O3 was nested in O2, then the second call to O2 could be internal.
>>>> But in that case, the first path would be impossible as O1 could not 
>>>> see O3
>>>> to call it.]
>>>>
>>>> Remember that the decision as to whether a call is internal or external
>>>> is
>>>> purely syntactic: if a protected object is given explicitly in the 
>>>> call,
>>>> one
>>>> needs to trigger the mutual exclusion mechanisms again. The only 
>>>> time one
>>>> doesn't need to do that is when the call does not include the object
>>>> (that
>>>> is, directly from the body of an operation).
>>>
>>> Even when the object in the call is statically known to be same?
>>
>> Yes. An external call *always* gets the lock again. I believe that was 
>> made
>> the rule to make it obvious as to what will happen based on the form of
>> call.
> 
> I mean this:
> 
>     protected body O is
>        procedure P1 is
>        begin
>           ...
>        end P1;
>        procedure P2 is
>        begin
>           P1;   -- OK
>           O.P1; -- Deadlock or Program_Error


That is an internal call, so no deadlock nor error.

See RM 9.5(4.e), which is this exact case.


>        end P2;
>     end O;
>