ReRe: why isolated components

Laszlo Varga <>
Fri Aug 22 14:14:03 CEST 2003


Hello,
it seems that we are getting understand each other.
At least we have no clear idea about what Joe want to have.
Really, it seems that the motivation is to have something
process based fault tolerancy or robustness or at least stability.
UBF is also behind the scene, what makes me suspicious.

Maybe I'm mistaken, but the main point in UBF - I think- the C level,
the contract. It makes an UBF contract much more strict then an IDL.
In other words, it specifies the dynamic behaviour while IDLs-are just static.

Is not the THING about building a contract-specified component system?

If it were, i'd like it.

Thanks for your time
Laszlo
 
> 
> Laszlo Varga wrote:
> > thanks for the "answer". Right, isolation reduces the (possible) complexity,
> > but is that the motivation for the wrapper project?
> 
> Well, *that* is another issue.
> 
> I don't know Joe's thoughts on the subject, but my impression is that 
> it's about coping with failures.
> If a subroutine crashes, or if it just detects an abnormal condition and 
> logs it, this is behaviour that punches right through to the top levels 
> of the application. The "let it crash" philosophy of Erlang says: if a 
> component fails, let if fail, and don't burden the caller (or service 
> requester or whatever you name it) with analysis of the crash details, 
> just tell it that the request failed.
> The toplevel may be unable to cope with the situation, but then passing 
> up crash details will introduce lots of coupling just for the rare case 
> of a crash - the resulting design mess just isn't worth the benefits.
> 
> Other languages handle this via exceptions.
> Eiffel got this right: Eiffel exceptions are unsuitable for passing up 
> information on a crash (apart from diagnostic information that helps 
> programmers and debuggers; there's no channel for passing up information 
> that would help the top-level to analyze the error).
> Java and C++ got it wrong: they make it all too easy to pass up 
> information that allows the caller to continue. The net result being 
> that exceptions create an additional, quite tight coupling between low 
> and high levels of the system. (It's no good if the top-level of a 
> system tries to handle an InternetConnectionFailure exception just 
> because an Internet resource wasn't available ten call levels below it...)
> 
> Erlang's idea is to separate the layers of processing into separate 
> processes, and to let the process crash. The advantage is that this 
> quite nicely handles any memory leaks that might occur on lower levels 
> (even garbage-collected languages can leak memory: when calling out into 
> C, or when accumulating larger and larger structures).
> I consider it a disadvantage that this interleaves the issues of crash 
> protection and asynchronous message passing. However, my Erlang 
> experience is *very* limited, so please consider the latter just an 
> uninformed opinion.
> 
> HTH
> Jo
> 




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