RFR: 8352088: Call of com.sun.jdi.ThreadReference.threadGroups() can lock up target VM [v6]

[Chris Plummer]

> Calling ThreadGroupReference.groups() from an event handler can cause a deadlock. Details in first comment. Tested with :jdk_lang on all supported platforms and tier1, tier2, tier3, and tier5 svc testing.

Chris Plummer has updated the pull request incrementally with one additional commit since the last revision:

  undo change that wasn't suppose to be committed.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24236/files
  - new: https://git.openjdk.org/jdk/pull/24236/files/3d241742..977ecf15

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24236&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24236&range=04-05

  Stats: 16 lines in 1 file changed: 0 ins; 16 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/24236.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24236/head:pull/24236

PR: https://git.openjdk.org/jdk/pull/24236