RFR: 8256811: Delayed/missed jdwp class unloading events [v17]

[Serguei Spitsyn]

On Thu, 21 Jul 2022 04:11:05 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> > The following RN is related to this question:
> > https://bugs.openjdk.org/browse/JDK-8256558
> > It explicitly says: `SetNotificationMode can be used to explicitly flush ObjectFree events, if needed.`
> 
> That wasn't quite what I was getting at. My comment / question was much more general. If you call SetEventNotificationMode() to disable a specific event, once it returns are you guaranteed that no more events will be delivered. This means that if JVMTI was in the middle of calling the event handler at the same time that SetEventNotificationMode() is called, then before returning, SetEventNotificationMode() will block until the event handler returns.

There is no such general guarantee with calls to the `SetEventNotificationMode`. It is not in the `JVM TI` spec. My view of the `JVM TI `design is that it is up to the native agents to provide synchronization if needed. For instance, I spent some time in the past to fix several problems related to the `JDWP` agent shutdown as the `WRONG_PHASE` error code was appearing in the middle of an event handler execution.

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PR: https://git.openjdk.org/jdk/pull/9168