RFR: 8355453: nsk.share.jdi.Debugee.waitingEvent() does not timeout properly

[Chris Plummer]

On Thu, 24 Apr 2025 15:34:40 GMT, Leonid Mesnik <lmesnik at openjdk.org> wrote:

>> nsk.share.jdi.Debugee.waitingEvent() takes a timeout argument. However, if the call to EventQueue.remove() times out and returns null, waitingEvent() just keep on retrying. The logic is incorrect for a null result. It should immediately throw an exception. The retry path is only meant for filtering out other events, and it updates "timeLeft' before retrying to avoid endlessly repeating the loop. 
>> 
>> Tested by running all of nsk/jdi locally on linux-x64-debug
>
> Marked as reviewed by lmesnik (Reviewer).

@lmesnik @alexmenkov I just noticed an inconsistency with my fix. If the code falls out of the while loop, it returns null, whereas the fix I added throws an exception if eventQueue.remove() times out. Initially I had fixed it by returning null here also, but the result of returning null meant an NPE in the caller in the one case I had where this code was timing out. However, that was new code I'm experimenting with that added a waitingEvent() call and didn't check the result, so it got an NPE. It seems that all other callers do check the result (via instanceof), so they would not result in an NPE. So perhaps the better choice here is to return null instead of throwing an exception.

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PR Comment: https://git.openjdk.org/jdk/pull/24839#issuecomment-2829055633