[squeak-dev] Re: Odd performance characteristics of symbol creation

Adrian Lienhard adi at netstyle.ch
Thu May 7 07:47:35 UTC 2009


Thanks Nicolas!

As expected, the performance graph is constant with your fix.

Your tests cover a lot of cases. Anything in particular one should  
test before integrating the fix?

Cheers,
Adrian

On May 7, 2009, at 01:45 , Nicolas Cellier wrote:

> Wait, there is a bug in scanFor: fixCollisionsFrom: does not recycle
> the first nil and scanFor: then loops indefinitely :( see
> http://bugs.squeak.org/view.php?id=7350 for update
>
> 2009/5/7 Andreas Raab <andreas.raab at gmx.de>:
>> Nicolas Cellier wrote:
>>>
>>> Created http://bugs.squeak.org/view.php?id=7350
>>
>> Thanks, this is great. Is this approach applicable to weak  
>> dictionaries as
>> well?
>>
>
> Should inquire, but it's getting late...
>
>> Cheers,
>> - Andreas
>>
>>> 2009/5/6 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>:
>>>>
>>>> Ah, I forgot to accept one change!
>>>> It's even better if we decrease the tally when recycling a nil  
>>>> slot in
>>>> #fixCollisionsFrom:
>>>>
>>>> Nicolas
>>>>
>>>> 2009/5/6 Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>:
>>>>>
>>>>> Though I have tried to attack it with some tricky combinations,  
>>>>> I did
>>>>> not found a problem with current implementation.
>>>>> It was funny to see how nil is handled as any other object in  
>>>>> WeakSet
>>>>> fixCollisionsFrom: (scanFor: nil works).
>>>>>
>>>>> However, it's a pity not to recycle all those nils until next  
>>>>> grow!
>>>>> Here comes a little trial for recycling reclaimed nil slots in  
>>>>> Pharo
>>>>> (seems compatible with 3.10.2).
>>>>> No guarantee... Note there is no WeakSet tests in Pharo nor 3.10.2
>>>>> currently :(
>>>>>
>>>>> Nicolas
>>>>>
>>>>> 2009/5/6 Andreas Raab <andreas.raab at gmx.de>:
>>>>>>
>>>>>> Nicolas Cellier wrote:
>>>>>>>
>>>>>>> Take this example:
>>>>>>
>>>>>> Ah, good point. (it works fine with o1 = 'g' and o2 = o3 = o4 =  
>>>>>> 'd').
>>>>>> The
>>>>>> thing is that the test in WeakSet>>add: was misleading - it  
>>>>>> tests for
>>>>>> nil
>>>>>> where scanFor: searches only for flag.
>>>>>>
>>>>>> Cheers,
>>>>>> - Andreas
>>>>>>
>>>>>>> ws := WeakSet new.
>>>>>>> array := WeakSet new instVarAt: (WeakSet allInstVarNames  
>>>>>>> indexOf:
>>>>>>> 'array').
>>>>>>> o1 hash \\ array size + 1 -> 1.
>>>>>>> o2 hash \\ array size + 1 -> 2.
>>>>>>> o3 hash \\ array size + 1 -> 1.
>>>>>>> ws add: o1; add: o2; add: o3.
>>>>>>>
>>>>>>> o1 := o2 := nil.
>>>>>>> Smalltalk garbageCollect.
>>>>>>> "o1 and o2 are reclaimed."
>>>>>>> (array at: 1) -> nil.
>>>>>>> (array at: 2) -> nil.
>>>>>>>
>>>>>>> o4 hash \\ array size + 1 -> 1.
>>>>>>> ws add o4.
>>>>>>> (array at: 1) -> o4.
>>>>>>>
>>>>>>> (ws includes: o3) -> false.
>>>>>>>
>>>>>>> I will try and build a test case. Should be easy with Fractions.
>>>>>>>
>>>>>>> 2009/5/6 Andreas Raab <andreas.raab at gmx.de>:
>>>>>>>>
>>>>>>>> Nicolas Cellier wrote:
>>>>>>>>>
>>>>>>>>> Isn't that dangerous if you don't fixCollisionsFrom: index ?
>>>>>>>>
>>>>>>>> Why would it? All this does is avoiding to update the tally  
>>>>>>>> ivar if
>>>>>>>> we're
>>>>>>>> replacing a previously reclaimed entry with a new value. And  
>>>>>>>> I don't
>>>>>>>> think
>>>>>>>> that #fixCollisionsFrom: even looks at tally.
>>>>>>>>
>>>>>>>> Cheers,
>>>>>>>> - Andreas
>>>>>>>>
>>>>>>>>> Nicolas
>>>>>>>>>
>>>>>>>>> 2009/5/6 Andreas Raab <andreas.raab at gmx.de>:
>>>>>>>>>>
>>>>>>>>>> Adrian Lienhard wrote:
>>>>>>>>>>>
>>>>>>>>>>> I haven't had time to look into this very closely yet but  
>>>>>>>>>>> maybe
>>>>>>>>>>> somebody
>>>>>>>>>>> else already knows what is going on. My guess is that the
>>>>>>>>>>> NewSymbols
>>>>>>>>>>> weak
>>>>>>>>>>> set is repeatedly grown since tally is not decreased if  
>>>>>>>>>>> the GC
>>>>>>>>>>> removes
>>>>>>>>>>> a
>>>>>>>>>>> weak element.
>>>>>>>>>>
>>>>>>>>>> That's an excellent guess. Try changing WeakSet to e.g.,
>>>>>>>>>>
>>>>>>>>>> WeakSet>>atNewIndex: index put: aValue
>>>>>>>>>> "Add newValue at the given index. Don't increment tally
>>>>>>>>>> if current slot is nil since a previous value has been  
>>>>>>>>>> collected"
>>>>>>>>>> (array at: index) ifNil:[^array at: index put: aValue].
>>>>>>>>>> ^super atNewIndex: index put: aValue
>>>>>>>>>>
>>>>>>>>>> Cheers,
>>>>>>>>>> - Andreas
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>
>>>
>>
>>
>>
>




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