RFR: CODETOOLS-7902923: jcstress: Eliminate dependency on Executors/Futures in forked VMs

[Aleksey Shipilev]

Forked VMs are executing the tests, and they are inherently using some concurrency primitives that might be under the test. Executors/Futures are the examples of such primitives. Since the jcstress uses are simple, we might as well do the hand-rolled implementations on bare Threads. This would improve test fidelity.

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Commit messages:
 - Avoid Executors/Futures

Changes: https://git.openjdk.java.net/jcstress/pull/51/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jcstress&pr=51&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7902923
  Stats: 277 lines in 7 files changed: 189 ins; 47 del; 41 mod
  Patch: https://git.openjdk.java.net/jcstress/pull/51.diff
  Fetch: git fetch https://git.openjdk.java.net/jcstress pull/51/head:pull/51

PR: https://git.openjdk.java.net/jcstress/pull/51