Hi Igor. Does the same test work correctlly in a interpreter VM? because I can see: ObjectMemory >> newObjectHash "Answer a new 16-bit pseudo-random number for use as an identity hash." lastHash := 13849 + (27181 * lastHash) bitAnd: 65535. ^ lastHash In which case, it seems that every new hash will be different than the previous one. But NewObjectMemory >> newObjectHash "Derive the new object hash from the allocation pointer. This is less costly than using lastHash because it avoids the read-modify-write cycle to update lastHash. Since the size of eden is a power of two and larger than the hash range this provides a well-distributed and fairly random set of values." <inline: true> ^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@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.
testBecomeIdentityHash "Note. The identity hash of both objects seems to change after the become:"
| 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.
self 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.
-- Mariano http://marianopeck.wordpress.com