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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: How to get Ada to ?cross the chasm??
Date: Sun, 6 May 2018 22:02:46 +0300
Organization: Tidorum Ltd
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Xref: reader02.eternal-september.org comp.lang.ada:52049
Date: 2018-05-06T22:02:46+03:00
List-Id: <comp.lang.ada>

On 18-05-06 12:53 , Dmitry A. Kazakov wrote:
> On 2018-05-06 10:34, Niklas Holsti wrote:
    ...
>> Moving the focus back to Ada, efficient applicative data structures
>> are interesting for real-time systems because they could reduce
>> locking/blocking times: a "reader task" could quickly grab a (logical)
>> immutable copy of a large data structure and read the data at its own
>> speed, without interfering with "writer" tasks that transform their
>> own (logical) copies of the data structure.
>
> You need to merge incoherent copies at some point later. More removed
> the point is, more difficult it becomes and more expensive could be a
> rollback, in case something happens.

One of the beauties of applicative data structures is that there is no 
need to roll back changes to a structure; if you keep a reference to the 
original structure, it remains valid (using more memory, of course).

The paper that Paul Rubin referenced has a nice example: when they 
changed their compiler's control-flow graph into an applicative 
structure, they could let the compiler perform some potential 
optimizations eagerly and early, before the optimization is known to be 
valid; if it turns out to be invalid, it can be "rolled back" simply by 
discarding the optimized version of the control-flow graph and returning 
to the un-optimized version.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .