<AWT Dev> Review request for 8165829: Android Studio 2.x crashes with NPE at sun.lwawt.macosx.CAccessibility.getAccessibleIndexInParent

[Anton Tarasov]

On 9/15/2016 1:50 PM, Sergey Bylokhov wrote:

> On 15.09.16 13:38, Anton Tarasov wrote:
>> The difference is that getAccessibleParent may return "null" to native
>> which is expected and handled, whereas getAccessibleIndexInParent may
>> throw NPE which is unexpected and not handled.
>> The problem occurs when unboxing null to a primitive wrapper
>> (Integer/Boolean etc). I've changed only those methods.
>>
>>> I think that it will be strange if getLocationOnScreen() will return
>>> null? Probably the old invokeAndWait(Callable,Component) should be
>>> updated to use this def value?
>>
>> The new invokeAndWait returns _requested_ default value which seems
>> better in general.
>
> Yes, and my suggestion was to use the new method and default values 
> everywhere instead of invokeAndWait(Callable,Component).

But the default value for a reference would be null, there's no need to 
request something else, unlike for primitive wrappers.

Or your idea is to force passing a def value anyway?

Anton.

>>> On 15.09.16 12:45, Anton Tarasov wrote:
>>>> Hello,
>>>>
>>>> Please review the fix:
>>>>
>>>> bug: https://bugs.openjdk.java.net/browse/JDK-8165829
>>>> webrev: http://cr.openjdk.java.net/~ant/JDK-8165829/jdk9/webrev.0
>>>>
>>>> (The bug is currently closed as “not an issue”, which is not quite 
>>>> true.
>>>> So once and if the fix is approved I can take the ownership of the 
>>>> bug).
>>>>
>>>> The problem is this. Sometimes when a frame is closed there may 
>>>> appear a
>>>> race condition:
>>>>
>>>> - removeNotify() is called on the frame on EDT and it removes all the
>>>> events associated with the frame from the event queue.
>>>>
>>>> - The frame is requested by accessibility via the CAccessibility 
>>>> static
>>>> methods (like CAccessibility.getAccessibleIndexInParent). Those 
>>>> methods
>>>> are called from native on AppKit thread and they perform via
>>>> invokeAndWait. The latter is wrapped with an InvocationEvent whose
>>>> source is set to the frame. But, once the event is put on the event
>>>> queue, it's purged by the removeNotify() call. As the result,
>>>> invokeAndWait returns null. Then, in some of the mentioned methods
>>>> 'null' is unboxed to a primitive 'int' or 'boolean' which results 
>>>> in NPE
>>>> propagated to native. On the native side, the NPE is not properly
>>>> handled and is just re-thrown.
>>>>
>>>> I don't have a simple and safe solution for the race. So, I suggest to
>>>> fix the NPE/crash at least.
>>>>
>>>> Thanks,
>>>> Anton.
>>>>
>>>>
>>>
>>>
>>
>
>