On Thu, May 10, 2012 at 10:16 AM, Chris Muller <asqueaker at gmail.com> wrote:

> >> I should add, it's already happened.  In 2009 Levente changed
> >> Object>>#identityHash to answer the scaledIdentityHash.
> >
> > Not in Squeak. Our IdentityDictionary uses scaledIdentityHash nowadays,
> but identityHash itself is left alone, answering the primitive value
> directly.
>
> I meant to say Object>>#hash, not #identityHash.
>
> So, before 12/1/2009:
>
>     true hash  "2950"
>
> but after 12/1/2009
>
>     true hash  "773324800"
>
> So, any saved persistent EToys ReferenceStream object-models files
> with true involved in the calculation of #hash prior to 2009 will now
> be goofed up unless you remember to rehash all regular Dictionary's
> after loading it.  The properties of this bug are:
>
>  - it is hidden, you had no idea it was there because no SUnit test
> can possibly catch it.  It didn't show until production.
>  - it is image-specific -- you load the file an image before
> Levente's change and everything seems fine.  What's going on?
>  - it is "intermittent" because there's a small possibility that, if
> the Dictionary were small, you might get lucky with a "hit" anyway
> when calculating the slot to start searching at
>  - it could lead to corrupt data model, because perhaps the app does
> something like #at:ifAbsentPut:, and maybe even on an
> otherwise-equivalent object, so you end up with TWO of the "same"
> object in the dictionary.  What a disaster!
>
> Now does it make sense?
>

No.  One *always* has to rehash on loading binary since one cannot
guarantee that identityHashes will be the same in the loading environment
as the saving environment.  It s a non-issue.

-- 
best,
Eliot
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20120510/f39e75d6/attachment.htm