On Tue, Sep 27, 2011 at 5:18 PM, Levente Uzonyi <leves@elte.hu> wrote:

On Tue, 27 Sep 2011, Mariano Martinez Peck wrote:

Hi. With this latest new #rehash there is a problem. I took Levente changes
from Squeak.
@Levente: the same happens in squeak so this may interest you.

The #rehash is right now

rehash

� | newInstance |
� newInstance := self species new: self basicSize - 1. "Make sure it has
the same capacity"
� 1 to: self basicSize do: [ :index |
� � � (self basicAt: index) ifNotNil: [ :key |
� � � � � newInstance at: key put: (array at: index) ] ].
� self copyFrom: newInstance

The problem is that #new: does:

new: numberOfElements
� "Create an instance large enough to hold numberOfElements without
growing. Note that the basic size must be a power of 2. It is VITAL (see
grow) that size gets doubled if numberOfElements is a power of 2"

� | size |
� size := self sizeFor: numberOfElements.
� ^(self basicNew: size) initialize: size

And #sizeFor: �does:

sizeFor: numberOfElements
� "Return the minimum capacity of a dictionary that can hold
numberOfElements elements. At least 25% of the array must be empty and the
return value must be a power of 2."

� ^1 bitShift: (numberOfElements * 4 // 3) highBit

So....the problem is that you always increase the size of the MD. So when
you do:
�newInstance := self species new: self basicSize - 1. "Make sure it has the
same capacity"
if fact you are creating a MD of a different size, which means that the
capacity is different and hence, using #copyFrom: �will create inconsisten
MD loosing methods, which causes the crash now.

You could add a

� newInstance capacity = self capacity
� � � ifTrue: [ self copyFrom: newInstance ]
� � � ifFalse: [ self becomeForward: newInstance ]

but that doesn't make sense because you always increase, so you will end up
using always the become.

I guess you can change to this:

� newInstance := self species new: self size. "Make sure it has the same
capacity"

but the problem is if in the future we change again #sizeFor.

So....I think a correct solution could be something like this:

� newInstance := (self species basicNew: self basicSize) initialize: self
basicSize. "Make sure it has the same capacity"

or..move that to MethodDict class side and do:

� newInstance := (self species newWithExactBasicSize: self basicSize)
"Make sure it has the same capacity"


newWithExactBasicSize: basicSize

� ^(self basicNew: basicSize) initialize: basicSize


what do you think ?

Nice find. I think your last suggestion is the way to go, though I'd call the method #newWithCapacity: instead of #newWithExactBasicSize:.

Thanks, I also think the better solution is the last one. Ok, I will take the suggestion of #newWithCapacity:
Now...what I am not sure is whether we could have this problem in another place apart from #rehash:.
For example, what about #removeAll:�� ?

If you can help me with that...

Cheers!

�

Levente

Cheers



On Sun, Sep 18, 2011 at 8:13 PM, Mariano Martinez Peck <
marianopeck@gmail.com> wrote:

On Sun, Sep 18, 2011 at 5:40 PM, Nicolas Cellier <
nicolas.cellier.aka.nice@gmail.com> wrote:

I'm not quite sure it is correct.
The problem is if another Process want to use this MethodDictionary
while it is in an inconsistent state...
Or if you are rehashing on of the MethodDictionary which contains one
of the methods used by the rehashing itself.

Interesting. Thanks Nicolas for the pointer.

See recent changes from Levente in trunk.

heheheheh it seems Levente is still reading the Pharo mailing list.
So...I took his commits of today, and I have made a Pharo change set.
I have put all the information here:
http://code.google.com/p/pharo/issues/detail?id=4826

Basically, he used #copyFrom: which is primitive and hence it avoids the
inconsistent state.

If someone can check the changeset and give the OK, we can integrate it.

Thanks a lot

�Nicolas

2011/9/17 Mariano Martinez Peck <marianopeck@gmail.com>:

On Sat, Sep 17, 2011 at 10:26 PM, Nicolas Cellier
<nicolas.cellier.aka.nice@gmail.com> wrote:

2011/9/17 Mariano Martinez Peck <marianopeck@gmail.com>:

Hi guys. I was checking MethodDictionary >> rehash and this is

terribly

slow
because of the #become. Then I saw #rehashWithoutBecome �but it

answers

a
different instance. I need a #rehash that does the rehash in the real
object
and answers self. So...I need the regular #rehash but I want to avoid
the
#become. Is that possible somehow?

This is the current implementation:

rehashWithoutBecome

� �| newInstance |
� �newInstance := self species new: self basicSize - 1. "Make sure

it

has
the same capacity"
� �1 to: self basicSize do: [ :index |
� � � �(self basicAt: index) ifNotNil: [ :key |
� � � � � �newInstance at: key put: (array at: index) ] ].
� �^newInstance

I am terrible bad with Collection and friends, but cannot we do
soemthing
like this:

rehashWithoutBecome

� �| newInstance |
� �newInstance := self species new: self basicSize - 1. "Make sure

it

has
the same capacity"

� �1 to: self basicSize do: [ :index |
� � � �(self basicAt: index) ifNotNil: [ :key |
� � � � � �newInstance at: key put: (array at: index) ] ].

� �1 to: newInstance basicSize do: [ :index |
� � � �(newInstance basicAt: index) ifNotNil: [ :key |
� � � � � �self at: key put: (newInstance array at: index) ] ].

� �^ self

I guess you should at least also copy the nil entries...
Maybe something like

1 to: newInstance basicSize do: [ :index |
� � � �self basicAt: index put: (newInstance basicAt: index).
� � � �array at: index put: (newInstance array at: index)].

Good point. So....I was not that mistaken ;)
I have just replaced CompiledMethod >> hash �with this new method and at
least all the tests in MethodDictionaryTest are green.
Do you think this implementation is correct or there can be problems?
because it is really MUCH faster than the original one.

Thanks in advance

Thanks for any help.


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