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From: kilgallen@eisner.decus.org (Larry Kilgallen)
Subject: Re: In Exception ?
Date: 1998/04/10
Message-ID: <1998Apr10.073734.1@eisner>#1/1
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Date: 1998-04-10T00:00:00+00:00
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In article <6gkafp$p31@drn.newsguy.com>, nabbasi@earthlink.net writes:

> Now, as I said, I did not know if one can associate an Ada procedure with
> a system interrupt. i.e. in the VMS example, I do not know if one can 
> make a VMS system service from Ada and pass an address of an Ada procedure
> to be called as an AST (say when the IO is completed). Since certainly
> one can call VMS system services from Ada (there is an Ada binding for
> that), I would think one can also do the above in Ada, but it been long
> time since I played on VMS so I can be wrong.

One can, indeed, do that, but DEC Ada recommends another approach.

> This sort of thing on VMS is not uncommon (programming with AST's), and it is
> flexible also, but needs careful programming to avoid problems with
> synchronizations between normal flow of code, and the AST flow of code.

A special AST_ENTRY construct allows the DEC Ada programmer to specify
an AST routine, but have that routine executed in normal (non-AST) mode
sometime after the AST fires.  This allows use of the AST mechanism in
concert with the synchronization rules of the Ada language.

Larry Kilgallen