Today I've had "fun" trying to fix a problem with our software (that uses
many processes running at various priorities). Due to the use of a
WeakIdentitykeyDictionary I was running into problems witht the dictionary
having multiple identical keys... not pleasant, especially when it gets to
around 27000 entries (should be 20).

I have traced the problem to the fact that finalisation is not thread-safe
with respect to access of said dictionary. As a fix I have implemented a
#critical: method on the WeakArray class that evaluates the given block with
a #critical: call on the FinalizationLock of WeakArray.

Access to the weak dictionary is now wrapped with a WeakArray critical:
[...] and the problems have, thankfully, disappeared.

I can post a Mantis entry for this if you all think it is appropriate. Just
wondering how many other places in existing Squeak code might trip up on
this.

Regards, Gary.