RFR: 8267079: Support async handshakes that can be executed by a remote thread [v2]

[Man Cao]

> Hi all,
> 
> Can I have reviews for this small refactoring change? It resolves a pending concern from [JDK-8238761](https://bugs.openjdk.java.net/browse/JDK-8238761), clarifies the code and allows more use case of async handshakes. See [JDK-8267079](https://bugs.openjdk.java.net/browse/JDK-8267079) for detailed description.
> 
> -Man

Man Cao has updated the pull request incrementally with one additional commit since the last revision:

  Added missing deallocation and renamed "remote" to "non-self".

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4005/files
  - new: https://git.openjdk.java.net/jdk/pull/4005/files/2e113fd0..01f4d3ff

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4005&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4005&range=00-01

  Stats: 15 lines in 2 files changed: 4 ins; 0 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4005.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4005/head:pull/4005

PR: https://git.openjdk.java.net/jdk/pull/4005