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From Tim Ellison <t.p.elli...@gmail.com>
Subject Re: [jira] Commented: (HARMONY-6009) [classlib][beans] NPE launching swingset2 example
Date Wed, 19 Nov 2008 10:34:14 GMT


Kevin Zhou wrote:
> Tim Ellison wrote:
>> Hi Kevin,
>>
>> Kevin Zhou wrote:
>>  
>>> I think this defect may be a thread-safe problem.
>>> I read HARMONY's PropertyChangeSupport code and found that:
>>> It employs ArrayList to store the property change listeners which is not
>>> thread-safe.
>>> This defect occurs in a private doFirePropertyChange method.
>>> This method may asynchronously use the list of
>>> PropertyChangeListener, which
>>> contains a null value when modification (add or remove) of the list
>>> has not
>>> finished.
>>>     
>>
>> Yes, I put in some trace code and there is a null stored in the
>> globalListeners list which causes the NPE.
>>
>> However, I don't see where that null could have been stored.  Can you
>> suggest what part of the code has stored the null in there?  Every add
>> to the list first checks for null.  I'll take a look and see if I can
>> catch it in the test.
>>
>> I won't apply your 'check-for-null' patch since I think that just masks
>> the underlying problem.
>>
>> Regards,
>> Tim
>>
>>   
> Hi Tim,
> This patch doesn't only check-for-null.
> It also changes the private doFirePropertyChange method to synchronized
> method. This may resolve the asynchronous operation on globalListeners
> list.

Yes, I saw that. How will that help?

> I will try to find what part of the code has stored the null.
> Due to license cares, I think it difficult to find the setting-null code
> which may be inside SwingSet2.jar.

But the globalListeners is a private variable, so the only way it can be
given a null element is if the code successfully calls a method that
adds a null, or we let the private List escape.  I don't see either of
those in the Beans code, do you?  Clearly I'm missing something for this
to happen.

Regards,
Tim

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