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Date: Tue, 18 Sep 2007 17:35:19 +0200
From: Daniel Fagerstrom <danielf@nada.kth.se>
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Subject: Re: pipelineComponent scope troubles
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Grzegorz Kossakowski skrev:
> Giacomo Pati pisze:
>   
>> Yes, clean my M2 repo.
>>
>>     
>>> of problematic behaviour in order to help anyhow.
>>>       
>> Still have the problems. With scpre="request" I got the stack trace after the first request found
>> at http://people.apache.org/~giacomo/request-log4j-2.log
>>     
>
> I fear that we got stuck. Without working code exhibiting your problem I cannot help any further.
>   
Don't know if you are going to like it ;) Have you studied how you prove 
algorithm correctness yet? If not, the idea is that you give a  formal 
definition of the precondition of the algorithm, what is true about 
input data before you run the algorithm. You also describe the post 
condition, what is supposed to be true about the output of the 
algorithm. The you use your creativity and state an invariant, something 
that will be true about the state variables of the algorthm at all time 
through the execution. Then the remaining and rather mechanical step is 
to show that the precondition and the operations leads to the invariant, 
that loops or recursions preserve the invariant and that the invariant 
together with the stop condition leads to the postcondition.

OK, doing the above in a formal way, would require an completely 
unrealistic amount of work for the object model and the pipeline scope. 
But following the general scheme in an unformal way is often quite 
helpful for understanding and describing complex algorthms.

So, getting to the point, what I propose is that you describe in a 
semiformal way what is supposed to be true about stack and other state 
before enetering the scope, during the scope and when leaving it. This 
will be helpful both for you and for the rest of us for being able to 
see if your approach and code is correct.

Now, the above can seem like a rather indirect and inneficient way to 
find the problem behind the bug that Giacomo found. For code in general 
it isn't the way to go. But for things like building execution machines 
for languages (as in the current case) my experience strongly suggest 
that what I propose is the most efficient way to go.

/Daniel