RFR: 8392: Memory view on MacOS keeps reverting to aggregate trace list

[Marcus Hirt]

Annoying issue.

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Commit messages:
 - Tracking and making the future cancellable for model updates
 - 8392: Fixing listener effect race by having one listener

Changes: https://git.openjdk.org/jmc/pull/647/files
  Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=647&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8392
  Stats: 23 lines in 2 files changed: 16 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jmc/pull/647.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/647/head:pull/647

PR: https://git.openjdk.org/jmc/pull/647