Summary

Obsolete the EmitSync flag.

Problem

The experimental EmitSync flag can in theory be used to select which implementation of the synchronization primitives to use. The flag was convenient when the various implementations were compared a long time ago.

In practice the only implementation that is used and tested today is the default one. The EmitSync flag no longer serves the purpose it used to, and is "Unsafe, Unstable" (the documentation of the flag says so explicitly). It should be obsoleted and later removed.

Solution

The EmitSync flag should be obsoleted.

Specification

The EmitSync flag will be obsoleted by adding it to the special flags table in arguments.cpp:

diff -r 091d35929686 src/hotspot/share/runtime/arguments.cpp
--- a/src/hotspot/share/runtime/arguments.cpp   Tue Sep 04 10:04:14 2018 -0700
+++ b/src/hotspot/share/runtime/arguments.cpp   Tue Sep 04 10:17:30 2018 -0700
@@ -574,6 +574,7 @@
   { "PrintSafepointStatisticsCount", JDK_Version::jdk(11),     JDK_Version::jdk(12), JDK_Version::jdk(13) },
   { "TransmitErrorReport",           JDK_Version::undefined(), JDK_Version::jdk(12), JDK_Version::jdk(13) },
   { "ErrorReportServer",             JDK_Version::undefined(), JDK_Version::jdk(12), JDK_Version::jdk(13) },
+  { "EmitSync",                      JDK_Version::undefined(), JDK_Version::jdk(12), JDK_Version::jdk(13) },

 #ifdef TEST_VERIFY_SPECIAL_JVM_FLAGS
   { "dep > obs",                    JDK_Version::jdk(9), JDK_Version::jdk(8), JDK_Version::undefined() },