[squeak-dev] The broken user interrupt, or the saga of 100000 factorial.

Bert Freudenberg bert at freudenbergs.de
Fri Jan 6 12:05:40 UTC 2012

On 23.12.2011, at 16:38, David T. Lewis wrote:

> On Fri, Dec 23, 2011 at 10:13:18AM -0500, David T. Lewis wrote:
>> On Fri, Dec 23, 2011 at 07:39:41AM -0500, Bob Arning wrote:
>>> I've seen suspicious behavior (tough time interrupting and lots of 
>>> finalization in MessageTally reports) in my 4.2 image, so I thought I'd 
>>> look at applying this fix. One thing I'm a little puzzled about: 
>>> HasNewFinalization is false in my image (I'm using a Cog that's a few 
>>> months old). Under what conditions is it true?
>> I think you have spotted a timing problem here. I put the initTestPair
>> and checkTestPair calls together in a startUp: method, which is
>> wrong because it does not give the VM an opportunity to do its
>> updates, so the results of the test are not valid.
>> This is not exactly elegant, but if you force a garbage collection
>> between initTestPair and checkTestPair, the test will work properly.
>> WeakArray class>>startUp: resuming
>> 	resuming ifFalse: [ ^self ].
>> 	"Check if new finalization is supported by the VM"
>> 	WeakFinalizationList initTestPair.
>> 	Smalltalk garbageCollect.
>> 	WeakFinalizationList checkTestPair.
>> 	self restartFinalizationProcess.
>> A better fix is needed - sorry about that. I'm not sure if I'll
>> have a chance to look at this today, but the important thing is
>> to arrange for the check to be done when the image is started,
>> but not to continue repeating the test after it has been
>> successfully performed.
> The following seems to take care of the issue without requiring
> anything to be done in the startUp: method.
>  WeakArray class>>finalizationProcess
>    | initialized |
>    initialized := false.
>    [FinalizationSemaphore wait.
>    initialized ifFalse: ["check VM capability once at image startup time"
>      WeakFinalizationList initTestPair.
>      Smalltalk garbageCollect.
>      WeakFinalizationList checkTestPair.
>      initialized := true].
>    FinalizationLock critical:
>      [FinalizationDependents do:
>        [ :weakDependent |
>        weakDependent ifNotNil:
>          [weakDependent finalizeValues]]]
>      ifError:
>      [:msg :rcvr | rcvr error: msg]] repeat
> I'll update this in the inbox. Bob, thanks for catching the error.
> Dave

Guess we should resume this discussion:

This is in trunk now, but if I uncomment the workaround in #openInterrupt:onProcess: I still can't break into 100000 factorial.

How to proceed?

- Bert -

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