RFR: 8269268: JDWP: Properly fix thread lookup assert in findThread() [v2]

[Kevin Walls]

On Thu, 24 Jun 2021 16:51:59 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Re-enable the assert that was disabled (with some overhead) by [JDK-8265683](https://bugs.openjdk.java.net/browse/JDK-8265683). Explanation is in the CR and also in comments included with the changes.
>> 
>> I tested by running `vmTestbase/nsk/jdb/suspend/suspend001/suspend001.java` and `vmTestbase/nsk/jdb/wherei/wherei001/wherei001.java` 100's of times, and did not see any failures. I also verified the original issue was still reproducible by temporarily not setting `gdata->handlingVMDeath = JNI_TRUE`, which did trigger the assert as expected.
>
> Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rename flag and make some minor adjustments.

Marked as reviewed by kevinw (Committer).

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PR: https://git.openjdk.java.net/jdk/pull/4580