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From: CTips <ctips@bestweb.net>
Newsgroups: comp.lang.ada,comp.realtime,comp.software-eng
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Tue, 08 Mar 2005 21:43:47 -0500
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Xref: g2news1.google.com comp.lang.ada:8904 comp.realtime:1097
 comp.software-eng:4654
Date: 2005-03-08T21:43:47-05:00
List-Id: <comp.lang.ada>

Martin Dowie wrote:
> CTips wrote:
> 
>> Will that generate:
>>   L0:
>>       lwlock temp,&Value
>>       add    temp,temp,1
>>       stwcond temp,&Value
>>       if( failed ) goto L0;
>> or will it generate something much more heavy-weight.
> 
> 
> If you need that particular assembler then you'd best write it yourself. 
> I don't know of any language that could guarentee what assembler is 
> produced following a compilation.
> 
> Cheers
> 
> -- Martin

But isn't it interesting that Ada can't express this?

Roughly speaking, Ada provides synchronous message passing and 
(non-nested?) monitors as first class constructs. This means that
  - it doesn't support asynchronous communication
  - it doesn't support any number of lock-free algorithms
Also, Ada's only scheduling/queing discipline is FIFO with priorities 
(and priorities are only available if the RT annex is actually 
implemented). If I want to do earliest-deadline first, well, how do I go 
about doing it?

Note that in most C compilers (NOT C++), it is possible to write the 
atomic increment code using inline assembler for the lwlock and stwcond 
and expect the code to be compiled correctly, and for the optimizations 
to optimize the code "correctly" (where correctly means that they'll do 
stuff like constant propagation etc. but won't change the atomic nature 
of the increment).

Also, its possible to use the full power of C and still co-exist with 
libraries that provide threading models of various kinds (e.g. POSIX).