Re: Question about the need for requeue as described in Rationale

[progers@acm.org]

In <31E16C28.3BE2@csehp3.mdc.com>, "James A. Squire" <m193884@CSEHP3.MDC.COM> writes:
>progers@ACM.ORG wrote:
>
>> Requeue is needed to deal with the difficulties associated with
>> "avoidance synchronization", which is the model used in Ada.
>> The most illustrative example IMHO is the lack
>> of expressive power of guard conditions in select statements:
>> the conditions may not refer to the formal parameters of the
>> accept statements they control.  Thus you sometimes have to
>> to do two rendezvous instead of one, and this leads to a
>> number of other difficulties: the race conditions and potential
>> for abort mentioned elsewhere.
>
>How is this different from barrier conditions on protected entries and
>procedures?

The same issue applies to protected entry barriers (protected
procedures don't have barriers).


>> See
>>
>>         A Problem With Ada and Resource Allocation, Ada
>>         Letters, vol. 3, no. 4 from 1984,
>>
>> or better yet, to hear how requeue works,
>>
>>         Burns & Wellings' Concurrency In Ada,
>>         Cambridge University Press, 1995
>
>I don't have access to either of these references.  Could you be a
>little more lucid?  The thrust of what you are saying went right by me.

Well, I think I was lucid when I wrote that :) but maybe I could have been
less succinct!  In any case, I strongly suggest you get access to the
Burns' and Wellings book, since you seem interested in the subject.

>--
>James Squire
>MDA Avionics Tools & Processes
>ja_squire@csehp3.mdc.com
>Opinions expressed here are my own and NOT my company's
>"one of these days I'm going to better myself by going to Knight school"
>"You'll be a web knight instead of a web page!"



pat
---------------
Patrick Rogers
progers@acm.org