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

["James A. Squire" <m193884@CSEHP3.MDC.COM>]

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?

> 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.
--
James Squire
MDA Avionics Tools & Processes
ja_squire@csehp3.mdc.com
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