[Zope] Zope Persistence (was: XML-RPC within ZOPE)

[Chris McDonough]

I don't understand the problem.  How is using XML-RPC incompatible  
with persistence?  What are you trying to exclude?

- C


On Dec 16, 2005, at 6:40 AM, Jan-Ole Esleben wrote:

> Thanks; this is a problem we are well aware of. Our solution is to
> increase the amount of workers, obviously.
>
> However, I'm increasingly getting a feeling that for a rather big
> range of unlikely situations that are nonetheless to be expected, Zope
> doesn't work _at all_. In a WebServices setting, situations like the
> one I described, with one server calling back to another server within
> a call from that latter server and both not knowing anything about the
> implementation of the other, it would most certainly be extremely hard
> to foresee the exact setup of such situations and impossible to
> exclude them for persistent objects that actually _do_ change state
> (unlike mine). The solution is to not have state in your objects, and
> thus lose instantly most of what Zope is.
>
> However, as I see it, the problem is that what Zope actually _is_
> (i.e. mostly the ZODB) is an unhealthy way of coupling data and
> implementation (which is _exactly_ why my implementation didn't work
> immediately). This of course comes from its origins in TTW development
> where there wouldn't actually have been many user made products.
>
> Please tell me if I'm wrong with my assumption above, and why. I'm not
> trying to be inflamatory, this just has me really worried.
>
> Ole
>
>
> 2005/12/15, Dieter Maurer <dieter at handshake.de>:
>> Jan-Ole Esleben wrote at 2005-12-11 19:10 +0100:
>>> Is it at all impossible to use XML-RPC _within_ a ZOPE architecture?
>>
>> In principle yes.
>>
>> Be careful however: it is easy to introduce deadlocks!
>>
>>   When during request processing you call back into the same
>>   Zope via XML-RPC, the calling out request will not complete
>>   until the XML-RPC returns a result (this always holds for
>>   calls, XML-RPC or other, to an external or internal server).
>>
>>   Zope has a limited amount of workers (the default is 4) able
>>   to execute requests. If there are no free workers, requests
>>   have to wait for one.
>>
>>   Now imagine that as many requests arrive as there are workers
>>   and each of them wants to perform an XML-RPC against the
>>   same Zope. Then you have a deadlock: none of the XML-RPC requests
>>   will finish, because there are no free workers. An no worker
>>   will ever become free again, because each of them waits for
>>   its XML-RPC to finish.
>>
>> Therefore, you should directly call internal resources (rather
>> than use XML-RPC).
>>
>>
>> --
>> Dieter
>>
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