RFR: 8291650: Add delay to ClassUnloadEventTest before exiting to give time for JVM to send all events before VMDeath

[Serguei Spitsyn]

On Mon, 1 Aug 2022 21:02:39 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

> Near the end of the test, the debuggee forces a GC so ClassUnloadEvents will be generated, and then the debuggee immediately exits. However, the ClassUnloadEvents might not be sent out before the VMDeath is generated, and it prevents delivery of any more events. A short delay after the GC should give the JVM time to deliver the ClassUnloadEvents first.
> 
> Note, I was not able to reproduce this issue, so I'm not 100% sure this will fix it. It does turn up in CI testing, so this seems worth trying to see if we still see it during CI.

This looks okay to me.
However, it can be still unreliable.
Is there a way to check-wait for the expected class unload events?

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PR: https://git.openjdk.org/jdk/pull/9708