[squeak-dev] identityHash bits not incremented for new objects?
Mariano Martinez Peck
marianopeck at gmail.com
Mon Aug 1 07:47:57 UTC 2011
Hi Igor. Does the same test work correctlly in a interpreter VM? because I
ObjectMemory >> newObjectHash
"Answer a new 16-bit pseudo-random number for use as an identity hash."
lastHash := 13849 + (27181 * lastHash) bitAnd: 65535.
In which case, it seems that every new hash will be different than the
But NewObjectMemory >> newObjectHash
"Derive the new object hash from the allocation pointer. This is less
using lastHash because it avoids the read-modify-write cycle to update
Since the size of eden is a power of two and larger than the hash range
a well-distributed and fairly random set of values."
^freeStart >> BytesPerWord
so...I have no idea, but maybe for two consequently allocated objects, the
instVar freeStart can remain with the same value ?
On Mon, Aug 1, 2011 at 8:43 AM, Igor Stasenko <siguctua at gmail.com> wrote:
> I found that #testBecomeIdentityHash sometimes failing, sometimes not.
> It seems like VM 'forgets' to produce different identityHash bits for
> two consequently allocated objects,
> while test assumes that they are always different.
> If i insert a statement (see the code), test no longer fails.
> "Note. The identity hash of both objects seems to change after the
> | a b c d |
> a := 'ab' copy.
> b := 'cd' copy.
> >>> [ b identityHash = a identityHash ] whileTrue: [ b := b copy ].
> c := a.
> d := b.
> a become: b.
> assert: a identityHash = c identityHash;
> assert: b identityHash = d identityHash;
> deny: a identityHash = b identityHash.
> A simple piece of code reveals the problem:
> (1 to: 20) collect: [:i |
> 'ab' copy basicIdentityHash ] #(954 954 955 955 956 956 957 957 958
> 958 959 959 960 960 961 961 962 962 963 963)
> Best regards,
> Igor Stasenko AKA sig.
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