thread-local data

[Diez B. Roggisch]

Emanuele D'Arrigo schrieb:
> Hi everybody,
> 
> Assuming a snippet such as:
> 
> threadLocalData = threading.local()
> threadLocalData.myDictionary = self.myDictionary
> 
> is it correct to say that threadLocalData.myDictionary is NOT a thread-
> local -copy- of self.myDictionary but it's actually pointing to the
> same object?

Yes, it's pointing to the same object, and it thus makes the whole 
purpose of threadlocal moot. Use a global.

 > If that's the case, and assuming I want to iterate over the dictionary
 > without it changing under my nose while I'm in the loop, would it be
 > better to encase the whole loop in lock-protected section or  would it
 > be better to make a copy of the dictionary first and then iterate over
 > that one? Given that in this particular thread I do not want to modify
 > the dictionary, conceptually a copy would work. But would making
 > thread-local copy be just as slow as making the whole loop thread
 > safe?

As MRAB pointed out - it depends. My gut feeling on this is that the 
copy-approach is fastest. Or even faster, if you can cope with keys 
getting lost while processing them:


for key in self.myDictionary.keys():
     try:
        value = self.myDictionary[key]
     except KeyError:
        pass


Diez