RFR: 8261391: ZGC crash - SEGV in RevokeOneBias::do_thread [v2]

[Robbin Ehn]

> Handshakes may contain oop Handles from the requesting thread.
> A handshake may be executed by another thread than the requester.
> We must make sure any such Handle is safe to use by other threads before executing the handshake.
> This change-set adds SWS::start_process() for the requesting thread also (we already do this for the target JavaThread).
> 
> Passes t1-5

Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - prepare() on self execution and a rename
 - Merge branch 'master' into 8261391-sws-handshaker
 - SWS start processing on handshaker

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2571/files
  - new: https://git.openjdk.java.net/jdk/pull/2571/files/83382d2d..7245e442

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2571&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2571&range=00-01

  Stats: 5728 lines in 102 files changed: 5090 ins; 407 del; 231 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2571.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2571/head:pull/2571

PR: https://git.openjdk.java.net/jdk/pull/2571