[squeak-dev] The Inbox: Collections-cbc.812.mcz

Eliot Miranda eliot.miranda at gmail.com
Mon Nov 19 03:16:46 UTC 2018

Hi Chris,

On Fri, Nov 16, 2018 at 3:11 PM Chris Muller <ma.chris.m at gmail.com> wrote:

> > Chris,
> > If/when we implement this, the idea is to rehash the collection using:
> >     HashedCollection rehashAll
> > Will this adverse affect your MagmaDictionary's?
> No, but it won't help them at all, either.
> Does anyone know if ReferenceStream automatially rehashes Dictionary's
> and Sets when it materializes them?  If not, then the impact of
> changing the hash calculation is much higher than if they do.

It has to, because:  Since Object>>#= and Object>>#hash fall back on #==
and #identityHash, then Dictionary, Set et al instances are potentially
affected by identity.  Therefore on reconstructing a Dictionary,. Set et al
instance an unpickler must rehash (*).

(*) unless it verifies that all elements implement their own #= and #hash,
which is intractable in practice; the only ways I can see of verifying that
an object does not use #== or #identityHash in its #= and #hash methods are

a) to analyze the code (impossible for a non-AI unpickler) or,
b) construct a shallow copy of an object (since lots of #= implementations
short-cut via "^self == other or: [...") and simulate #= and #hash, t5o see
if #== or #identityHash is sent

Either of these would slow down unpicking enormously; rehashing invokes #=
and #hash any way, but at full execution speed.

> Magma does, so no action should be needed for regular Sets and
> Dictionary's.
> > Or will those be handled some other way?
> However, Magma has another special dictionary called a MagmaDictionary
> which is designed to be larger than RAM.  It maintains a reference to
> its 'session', which communicates with the server to access the large
> dictionary contents straight from the disk.  If I have Intervals in
> any of these, I'll have to manually plan to rebuild them from scratch
> with a utility script(s), because they don't support rehashing the way
> small, in-memory HashedCollections do.
>  - Chris

best, Eliot
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