On Thu, Dec 31, 2009 at 2:33 AM, Marcus Denker <marcus.denker@inria.fr> wrote:

On Dec 31, 2009, at 9:50 AM, St�phane Ducasse wrote:

> Probably the changes of Martin von Lowis.

Yes. The changeset had code to migrate all instances... it might be that the debugger's use
of WeakKeyDictionary was added by Eliot? This would explain why it was not migrated.

Yes, DebuggerMethodMap is mine. A DebuggerMethodMap maps between the vector of temp names in the lower right-hand debugger window and temp locations in method activations. This is much more complex using closures tan blue-book blocks since in-scope temps are spread from a closure through its nested closures out to the home method. The cache holds the maps for the most recent N methods inspected with the debugger (N=16). The cache is weak so as not to hold onto methods that get deleted or redefined.

As far as registering the cache for finalization or not, I would defer to someone familiar with Squeak weak collections. I think I'm right in thinking that in VW a weak dictionary will be automatically finalized and will keep its tally correct. One only needs to register for finalization if something needs to happen besides simply removing elements. So when I implemented this in Squeak I could easily have got things wrong.

I suggest to just do the reset in a postscript in one of the next updates, and it's fixed.

> I imagine that when marcus is bad from holidays he can tell us more.
>

I'm back... kind of. Decided not to travel to south germany this morning after moving boxes
for 3 days... better to have an IKEA-unboxing-relaxing-reading-emails-hacking-weekend.

Marcus

> Now I try to reproduce it in 11128.
>
> I put a self halt in a method and execute the method.
> And I got no problem.
> After I tried to select 'self halt' + doit in the debugger itself and it worked too.
>
> Did you have a way reproduce it systematically ?
>
> Stef
> On Dec 31, 2009, at 4:17 AM, Martin McClure wrote:
>
>> This one's pretty nasty.
>>
>> Symptom:
>>
>> The debugger in recent and current 1.1 images is completely broken.
>>
>> To reproduce (save your image first!):
>>
>> "self halt" doit. It goes into an infinite loop, and if there's a way to
>> get out of that without killing the VM I'd like to know about it. Alt-.
>> works, but just tries to open another debugger, which goes into another
>> infinite loop, etc.
>>
>>
>>
>> Cause:
>>
>> DebuggerMethodMap>MapCache is a WeakIdentityKeyDictionary, but it is
>> corrupt. It has an array of 22 nils, expired is 0, so it contains
>> nothing, but tally=16.
>>
>> This causes MapCache to lie about its size.
>>
>> This drives DebuggerMethodMap class>>cacheDebugMap:forMethod: into an
>> infinite loop, the whileTrue: condition is always true, it keeps trying
>> to remove non-existent elements to get the size to be less than 16 but
>> the size is always 16.
>>
>> I don't see any obvious code paths to get into this state. I suspect it
>> may have been left in this state when weak collections were updated with
>> the new code not too long ago.
>>
>>
>> Cure:
>>
>> In an inspector, set tally=0. Debuggers then work again.
>>
>> Not sure how to package this as a slice, so I'll leave the update to
>> someone else, and get back to hashing, which was hard when every
>> walkback froze my system :-)
>>
>>
>> Regards,
>>
>> -Martin
>>
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>
>
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