RFR: JDK-8317920: JDWP-agent sends broken exception event with onthrow option [v4]

[Johannes Bechberger]

On Tue, 17 Oct 2023 21:37:05 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Yes, so the current way is probably ok?
>> 
>> IDEs like IntelliJ properly handle the exception event that is sent and don't report an error, so I don't see a problem.
>
>> On the other hand, I think if the debug agent requires that a handler be in place (as a result of the debugger creating and enabling the EventRequest) in order for onthrow to send the event, then the handler creation might come too late, and the event will get filtered out.
> 
> I was thinking that maybe suspend=y is the way around this for the debugger. This will cause the debug agent to do a SUSPEND_ALL before sending the ExceptionEvent. However, the event could still be received by the debugger before the debugger has setup the ExceptionRequest. The only thing suspend=y is really doing here is ensuring that all threads get suspended when the event is generated. In fact that makes it even more important that the debugger process the event. Otherwise it won't be doing eventSet.resume(), and execution will come to a stand still.
> 
> I think we might just be stuck with what we have now. My main concern then is that it is neither spec'd nor documented well. I'll file a separate CR to cover that.

I'm happy to help with any documentation efforts, as the lack of proper documentation is probably one of the reasons why the adoption was so low over the last twenty years.

The documentation should tell the potential users about the possible issues with this option.

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PR Review Comment: https://git.openjdk.org/jdk/pull/16145#discussion_r1362829727