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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: Interfacing with C: access/out parameters
Date: Tue, 31 Aug 2004 11:41:48 +0200
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Date: 2004-08-31T11:41:48+02:00
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Jeffrey Carter wrote:
> 1. What are the explicit timing requirements for this software?
> 
> 2. Does it fail to meet these requirements?
> 
> 3. If so, is eliminating this assignment the only way to meet the timing 
> requirements?
> 
> I have never encountered SW where these could all be answered "Yes".
> 
> Probably you don't want your software to be using C-convention types for 
> anything except the interface to C, so you'd want your thick binding to 
> have an Ada-convention type for Datum, and assign the fields of Helper 
> to it. Horrors! Multiple assignments!

Thanks for the responses and sorry for the error in the example.

As you have already guessed, I want to get rid (if possible) of the 
copy. I can't say for sure that my soft answers "yes" to your three 
questions, but evaluate for yourself:

I'm writing a (initially thin) binding for the Player/Stage robot server 
(http://playerstage.sf.net). The function we are talking about is a 
generic message passing one were messages are normally little (up to 
8kB) but could be (almost) arbitrarily bigger. Message communication 
occurs at a configurable pace but the default is 10Khz if memory serves 
well.

As you see, is a function which is used often, by other, more 
specialized communication functions. Being a binding, any code using it 
would pass by this "bottleneck".

It's for these reasons that I would want to have the optimal high level 
solution, and eliminating the copy of the returned data seems a sensible 
  desire. There is that mentioned Import_Valued_Procedure in Gnat which 
addresses this Ada shortcoming, but talking about a binding, I want it 
to be totally portable if possible.

As per the C convention types all around the place, my intention is to 
build (if time permits) a thick binding over this thin binding, so that 
can be isolated later.

Further ideas? Is there anything definitely unadvisable in my original 
solution? (The one using limited/tagged types and 'Address).

Thanks!