RFC: Cease JDK 9 support for Shenandoah

[Aleksey Shipilev]

JDK 9 is EOL, upstream does not accept patches for it. Download stats seems to indicate the small
amount of users that used 9 moved on to 10.

So, print the warning below in sh/jdk9, and give up supporting it. We would ask ops@ to seal the
sh/jdk9 repo too to avoid accidental pushes there. This would leave us with sh/jdk8 (current LTS),
sh/jdk10 (current STS), and sh/jdk (current-dev) as supported/developed JDKs.


diff -r 82415e2b3b0f src/share/vm/runtime/arguments.cpp
--- a/src/share/vm/runtime/arguments.cpp	Thu May 03 13:27:01 2018 +0200
+++ b/src/share/vm/runtime/arguments.cpp	Mon May 14 12:49:06 2018 +0200
@@ -2057,6 +2057,11 @@
 }

 void Arguments::set_shenandoah_gc_flags() {
+  log_warning(gc)("*******************************************************************");
+  log_warning(gc)("*    Shenandoah GC support for this JDK release had ceased.       *");
+  log_warning(gc)("*    JDK 9 is a short-term release, and it is superseded by 10.   *");
+  log_warning(gc)("*    Use this build at your own risk.                             *");
+  log_warning(gc)("*******************************************************************");

 #if !(defined AARCH64 || defined AMD64 || defined IA32)
   vm_exit_during_initialization("Shenandoah GC is not supported on this platform.");


Testing: see that warning message is printed

Thanks,
-Aleksey