On 2 August 2011 14:18, Henrik Johansen <[email protected]> wrote:
>
> On Aug 1, 2011, at 8:43 53AM, Igor Stasenko 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.
>
> What is the point of this test in the first place?
> To me it seems to test whether a VM's implementation of become: adheres to
> some properties.
> At least, VM bugs in traversal of references during become is the only way I
> could see the two first asserts EVER being false.
>
> As for the last assert (well, deny actually), in the context of what it's
> supposed to test as established above, it seems to me to say a VM should
> never give the same identityHash to subsequently copied objects. Which means
> a) It has nothing to do with become and identityHash, thus is in the test.
> b) Is this a property any code actually rely on?
>
> If not, why would we assert such a restriction on the VM implementation, or
> is it harmless?
>
> Either way, modifying the test to iterate till they ARE different, would make
> it meaningless in either case (and possible infinite loop in case of a really
> bad VM).
>
There is strong reason to test identityHashes, because VM should
preserve an identity hash for oops.
But of course test is wrong , because to test that , it should be like
following:
| a b hash1 hash2 |
a := 'ab' copy.
b := 'cd' copy.
hash1 := a identityHash.
hash2 := b identityHash.
a become: b.
self
assert: a identityHash = hash1;
assert: b identityHash = hash2.
--
Best regards,
Igor Stasenko AKA sig.
