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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: is there a version of unix written in Ada
Date: Fri, 2 Oct 2020 22:14:49 -0500
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"J-P. Rosen" <rosen@adalog.fr> wrote in message 
news:rl6lka$ccv$1@dont-email.me...
>
> Le 02/10/2020 à 08:56, Dmitry A. Kazakov a écrit :
>> On 02/10/2020 07:36, J-P. Rosen wrote:
>>
>>> To continue on Randy's response: mutual exclusion is not blocking.
>>> "Blocking" (as in "potentially blocking operation") means "being put on
>>> a queue", i.e. when the waiting time is potentially unbounded.
>>
>> It would be a poor definition, because deadlock in not bounded as well.
>> If jumping from one protected object to another is legal, we can
>> construct a deadlock out of mutual exclusion.
> But this would necessarily involve an "external call to the same
> protected object", which is defined as a potentially blocking operation.

Note that such an operation doesn't really block, it is a deadlocking 
operation; Ada lumped it into "potentially blocking" in order to save some 
definitional overhead. (A mistake, in my view, it should simply have been 
defined to raise Program_Error or maybe Tasking_Error.) "Potentially 
blocking", in normal use, means something else.

                 Randy.