[Twisted-Python] Shared resource manioulation example

[vitaly at synapticvision.com]

Of course its up to me to determine if it's a data collision or not,
but I was thinking may be Twisted can provide me with some already  
existing mechanism of its own. After all its already a pretty massive  
and complicated framework with tons of capabilities ...

But I'd like to get back to the point of the question: if at some  
point EventA callbacks and EventB callbacks need to work on the same  
global variable, than what would be a Twisted way (if exist) to  
prevent data collision ?

Thank you.

Quoting Nitro <nitro at dr-code.org>:

> Am 28.05.2010, 20:34 Uhr, schrieb <vitaly at synapticvision.com>:
>
>> hi,
>>
>> Callbacks serialization is clear to me.
>>
>> I'll try to rephrase the question: two requests are incoming for
>> reactor()
>> to handle. Each request has its own chain of callbacks.
>> At some point one of the requests need to update the same
>> global data structure, and another request need to delete from the same
>> global data structure.
>> So theoretically, correct me if I wrong, will be a data collision.
>> If it is, than how can I prevent it? Example please.
>
> It will go like this:
>
> reactor loop:
>
> 1) receive Event A
>     - fire deferred callback
>     - deferred callback does data[key] = value
> 2) receive Event B
>      - fire deferred callback
>      - del data[key]
>
> So one event is processed after another. Determining if it's a data
> collision is up to you. E.g. you could use something like a revision
> number. Each time you change the dictionary, increase it by one. Then if
> you try to change the dictionary and the client gave a different revision
> id then the last one, you know there is a collision.
> What you do sounds very much like database transactions. Those are not
> easy to do. One example is the ZODB which can do what you want. For
> example via BTrees. But I guess there are more lightweight systems which
> do what you want, too. It all depends where you want to go with your app.
> That's up to you though and not really a question in regards to twisted or
> networking.
>
> -Matthias
>
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