[OpenJDK 2D-Dev] [10] RFR: JDK-8188083- NPE in java.awt.image.FilteredImageSource.startProduction

[Philip Race]

The screenshot shows you directly calling this method in your test which
the documentation says you are not supposed to do.
So I am not able to be 100% sure that the test you have re-creates what
the submitter saw .. in his stack trace you have below it seems to be valid.

But to have a NPE at line 181 is odd.

  181             proxies.put(ic, imgf);


What is null ? proxies was just initialised in this same method so
I don't see how it can be null unless something elsewhere is
resetting it to null.

The only place I see that is removeConsumer

  138     public synchronized void removeConsumer(ImageConsumer ic) {
  139         if (proxies != null) {
  140             ImageFilter imgf =  proxies.get(ic);
  141             if (imgf != null) {
  142                 src.removeConsumer(imgf);
  143                 proxies.remove(ic);
  144                 if (proxies.isEmpty()) {
  145                     proxies = null;
  146                 }
  147             }
  148         }
  149     }

Now that method is synchronized .. OK so I think it might make sense
to mark the additional methods synchronized too but then I automatically
worry about introducing a deadlock.

I can't say for sure that you have done so however and likely there
are no nested locks here so it is probably OK but please run as many
tests as you can find to try to ensure that.

Adding or removing sychronized is binary compatible but since
these are public API methods you should still do a CSR
before pushing if this ends up being the approved fix.

-phil.




On 10/25/17, 11:58 PM, Prahalad Kumar Narayanan wrote:
> Hello Sergey
>
> Thank you for the suggestion.
>
> I 've updated JBS with below information.
>     1 . Stack trace information as provided by submitter-
>          java.lang.NullPointerException
>              at java.awt.image.FilteredImageSource.startProduction(FilteredImageSource.java:181)
>              at java.awt.image.FilteredImageSource.startProduction(FilteredImageSource.java:183)
>              at sun.awt.image.ImageRepresentation.startProduction(ImageRepresentation.java:732)
>              at sun.awt.image.ToolkitImage.addWatcher(ToolkitImage.java:221)
>      2. Screenshot showing the occurrence of the exception at FilteredImageSource.java: 181.
>              . The image also shows the test passing with JDK10 containing the fix on VM running Linux Ubuntu x64.
>
> Thank you
> Have a good day
>
> Prahalad N.
>
> -----Original Message-----
> From: Sergey Bylokhov
> Sent: Thursday, October 26, 2017 12:05 PM
> To: Prahalad Kumar Narayanan; 2d-dev
> Subject: Re: [OpenJDK 2D-Dev] [10] RFR: JDK-8188083- NPE in java.awt.image.FilteredImageSource.startProduction
>
> Hi, Prahalad.
> Can you please add a stack trace which include a line numbers to the bug report? Currently it is unclear in what line an exception is occurred.
>
> On 25/10/2017 21:07, Prahalad Kumar Narayanan wrote:
>> Hello Everyone
>>
>> Good day to you.
>>
>> Kindly review a fix for the bug
>>       Bug ID: JDK-8188083
>>       Description: Null Pointer Exception in
>> java.awt.image.FilteredImageSource.startProduction
>>
>> Root Cause
>>       . FilteredImageSource implements ImageProducer interface
>>       . All the methods of FilteredImageSource operate on a common data -HashTable, but only a few are synchronized methods.
>>       . Thus, when synchronized&  un-synchronized methods access / modify the hash table in a multi-threaded scenario, it renders the class vulnerable to this exception.
>>
>> Exception occurrence
>>       . The submitter has mentioned that there is no test-case to reproduce to this issue.
>>       . Luckily I was able to observe this issue with a "crude" test code
>>             . The test triggered 7k threads in an ExecutorService randomly adding/ removing/ invoking startProduction on FilteredImageSource object.
>>             . I didn't feel it robust enough to be added as a part of regression tests. I tried optimizing the test but in vain.
>>             . Hence the test code isn't added to the webrev.
>>
>> Details on the Fix:
>>       . The concerned methods have been "synchronized" in the fix.
>>       . No new regression failures were observed with this change.
>>
>> Kindly review the change and provide your feedback.
>> In addition, kindly suggest whether this requires CSR as it adds "synchronized" to method signature.
>>
>> Review Link: http://cr.openjdk.java.net/~pnarayanan/8188083/webrev.00/
>>
>> Thank you for your time in review
>> Have a good day
>>
>> Prahalad N.
>>
>>
>>
>>
>>
>
> --
> Best regards, Sergey.
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