RFR: 8281615: Deadlock caused by jdwp agent [v4]

[David Holmes]

On Thu, 17 Feb 2022 02:11:13 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> I agree. This code is called when the debug agent receives a CLASS_UNLOAD EventRequest (which the debug agent handles by requesting JVMTI GC_FINISH events). So there is nothing that prevents `classTrack_processUnloads()` from being called at the same time.
>
> In that case the `classTrack_processUnloads` is racing with the `classTrack_activate` call. I would not expect it to be possible to generate an event in relation to this before things have been "activated". But moving on ...

Okay I see from later comments that in fact no such race exists, but we have to synchronize with cbTrackingObjectFree

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PR: https://git.openjdk.java.net/jdk/pull/7461