hg: jdk/sandbox: 8230594: Allow direct handshakes without VMThread intervention

[chris.hegarty at oracle.com]

Changeset: e2bc57500c1b
Author:    pchilanomate
Date:      2020-01-22 16:46 +0000
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/e2bc57500c1b

8230594: Allow direct handshakes without VMThread intervention
Summary: Introduce direct handshakes and enable it for biased locking revocations.
Reviewed-by: dholmes, dcubed, coleenp, rehn

! src/hotspot/share/runtime/biasedLocking.cpp
! src/hotspot/share/runtime/handshake.cpp
! src/hotspot/share/runtime/handshake.hpp
! src/hotspot/share/runtime/mutexLocker.cpp
! src/hotspot/share/runtime/safepoint.cpp
! src/hotspot/share/runtime/safepointMechanism.inline.hpp
! src/hotspot/share/runtime/thread.cpp
! src/hotspot/share/runtime/thread.hpp
+ test/hotspot/jtreg/runtime/handshake/HandshakeDirectTest.java