[OpenJDK 2D-Dev] Fix for JDK-8139192 : Custom ImageFilters return blank images in Java 8(.45) while working in 7

[Jim Graham]

That looks good, but I wonder if it should catch all exceptions instead of just NPE.  Historically we were only catching 
NPE before we added the call to STATICIMAGEDONE, and the current filter in question turns out to throw an NPE, but if a 
filter that was commonly used with offscreen images was not expecting the STATICIMAGEDONE as was this WaterFilter, then 
they could potentially throw a wider variety of exceptions.

I'm good with NPE since that is the only case we've seen, but I'd also be good with changing line 192 to catch all 
exceptions.  Phil?

			...jim

On 5/27/16 1:32 AM, Ajit Ghaisas wrote:
> Hi Jim,
>
>     Thanks for in-depth analysis and detailed review.
>     I appreciate your concern for filtered image being blank in Java 8, while it used to work in Java 7.
>
>     Yes. I totally agree with your suggestion to do both -
>     1. Not send IMAGEERROR if there is exception from ImageFilter while processing STATICIMAGE done
>     2. At the same time, as we are consuming the exception, show the exception stacktrace.
>
>     With this fix the functionality of com.jhlabs.image.WaterFilter is restored. It does not return blank images anymore.
>     Also, as additional information, exception details are shown as a stacktrace.
>
>     Please review the updated webrev :
>     http://cr.openjdk.java.net/~aghaisas/8139192/webrev.02/
>
> Regards,
> Ajit
>
>
> -----Original Message-----
> From: Jim Graham
> Sent: Thursday, May 26, 2016 4:57 AM
> To: Sergey Bylokhov; Ajit Ghaisas; 2d-dev; Philip Race
> Subject: Re: [OpenJDK 2D-Dev] Fix for JDK-8139192 : Custom ImageFilters return blank images in Java 8(.45) while working in 7
>
> Their complaint is that the resulting image is empty - most likely because the error gets passed through and clears the image buffer.  It appears that the sequence of events is:
>
> We send SINGLEFRAMEDONE.
> - the image is displayable
> We send STATICIMAGEDONE.
> - filter throws NPE
> - image is probably still displayable
> We send ERROR
> - if it gets passed through to the toolkit image consumer then we'll clear the image buffer
> - image is no longer displayable
>
> It's hard to say for sure without having an instance of their filter in-house for testing, but previously we weren't sending the STATICDONE notice and the program was working just fine.  Since the NPE comes from their code when we send it, it shouldn't have affected any down-stream consumers, so we should be OK with just continuing on and the image should still be displayable just as if we hadn't sent the STATICDONE notice in the first place.
>
> Now, *during debugging*, they were thwarted by the fact that we ate the exception, true, but the original issue is that the image wasn't displayable at all.  We might want to do both:
>
> - not send ERROR for STATICDONE when we used to not send STATICDONE at all
> - show the exception so that someone realizes that there is a problem, even though we've made it not hurt their functionality.
>
> Does that make sense?
>
> 			...jim
>
> On 5/25/2016 1:36 PM, Sergey Bylokhov wrote:
>> On 25.05.16 23:33, Jim Graham wrote:
>>> How about option 3 -
>>>
>>> NPE before imageComplete sends an ERROR as it does now.
>>>
>>> NPE during imageComplete is ignored, both for backwards compatibility
>>> and because it is more of a "hint" than an operation that requires
>>> action from the consumer.
>>
>> I guess the case is that when we ignore this NPE(w/o any notification)
>> the users complains that the bug is in jdk.
>>
>>>
>>>             ...jim
>>>
>>> On 5/25/2016 1:31 AM, Ajit Ghaisas wrote:
>>>> Hi
>>>>
>>>>
>>>>
>>>> Bug :
>>>>
>>>> https://bugs.openjdk.java.net/browse/JDK-8139192
>>>>
>>>> Custom ImageFilters return blank images in Java 8(.45) while working
>>>> in 7
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Root cause :
>>>>
>>>> private method produce() in OffScreenImageSource.java consumes a
>>>> NullPointerException that originates from a custom ImageConsumer (a
>>>> 3^rd party image library class - com.jhlabs.image.WaterFilter)
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Analysis:
>>>>
>>>> 1. How the behavior changed between JDK7 and JK8 :
>>>>
>>>> A call to imageComplete(ImageConsumer.SINGLEFRAMEDONE) was added in
>>>> addition to imageComplete(ImageConsumer. STATICIMAGEDONE)  as a fix
>>>> for JDK-7143612.
>>>>
>>>>
>>>>
>>>> 2. What debugging revealed:
>>>>
>>>> A NullPointerException is being thrown from the library during the
>>>> call to imageComplete(ImageConsumer.STATICIMAGEDONE)
>>>>
>>>>
>>>>
>>>> 3. It looks like the fix of JDK-7143612 is valid and successive
>>>> calls to
>>>> imageComplete() are allowed.
>>>>
>>>>
>>>>
>>>> 4. The 3rd party library behavior appears incorrect (if it can not
>>>> handle subsequent calls to imageComplete(), it should de-register
>>>> itself).
>>>>
>>>> The 3rd-party library code should be fixed.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Possible modifications in JDK  :
>>>>
>>>>
>>>>
>>>> Currently, OffScreenImageSource::produce() consumes the
>>>> NullPointerException - this is incorrect and results in silent
>>>> failure of this particular image filter.
>>>>
>>>> We need to let the image filter library know that exception has
>>>> occurred in its code and not in JDK. We have two options -
>>>>
>>>>
>>>>
>>>> Option 1 : Rethrow the NullPointerException   --- It is the clearest way
>>>> to let 3^rd party library know that their code is erroneous with
>>>> latest JDK. This will change the 3^rd party image filter behavior
>>>> that generates blank image.
>>>>
>>>> Option 2 : Add a stack trace where the exception is being consumed
>>>> --- Adding stack trace provides more information regarding failure
>>>> of 3^rd party image filter with retaining the current behavior that
>>>> generates blank image.
>>>>
>>>>
>>>>
>>>> I have implemented both the options:
>>>>
>>>> Option 1: http://cr.openjdk.java.net/~aghaisas/8139192/webrev.00/
>>>>
>>>> Option 2:  http://cr.openjdk.java.net/~aghaisas/8139192/webrev.01/
>>>>
>>>>
>>>>
>>>> Request you to review both the webrevs and provide your preference.
>>>>
>>>> I will add a test to the selected webrev.
>>>>
>>>>
>>>>
>>>> Regards,
>>>>
>>>> Ajit
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>
>>