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Newsgroups: comp.lang.ada
Date: Thu, 29 Oct 2015 05:38:36 -0700 (PDT)
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Subject: Re: Asynchronicity and Promises
From: brbarkstrom@gmail.com
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Xref: news.eternal-september.org comp.lang.ada:28112
Date: 2015-10-29T05:38:36-07:00
List-Id: <comp.lang.ada>

On Wednesday, October 28, 2015 at 2:46:37 PM UTC-4, Dmitry A. Kazakov wrote:
> 
> > There's an interesting blog on Asynchronicity and Promises at
> [...] 
> > I think we've had some discussion in other e-mail threads here.
> > As far as I've been able to follow the discussion, we don't seem
> > to have settled the issue about how Ada could handle contract
> > "Promises" - although it looked like we had begun to converge
> > on some useful potential approaches.
> 
> Ada had this since Ada 95 in the form of a protected object. Protected 
> object's state is waitable. That gives you everything you need to design 
> things described. They are not 100% asynchronous because the caller waits 
> for the callee at some point anyway.
> 
> As a side note, usefulness of this approach is questionable. I can judge, 
> because this sort of objects and asynchronous execution has been used in 
> the middleware for 20+ years. A lot of use cases to be sure. It is 
> certainly neither natural nor composable and works at the low level only. 
> To be honest, I know no better way, but you must clearly understand 
> limitations of the approach, e.g. a total lack of scalability. Ada's 
> concurrency model has much more to offer and at the higher level as well.
> 
> P.S. What wonders me is that the author is seemingly unaware of 30+ years 
> of OS having asynchronous I/O and waitable objects. Just google for Windows 
> GetOverlappedResult.
> 
> -- 

Thanks for the response.  I'll take a look.

Bruce B.