RFR: Let ExplicitGCInvokesConcurrent be off by default

[Aleksey Shipilev]

Christine argues the default behavior for System.gc() should be left as Full STW GC. This patch does
it, while leaving the possibility to turn it the concurrent cycle back on.

$ hg diff
diff -r 096345a40169 src/share/vm/runtime/arguments.cpp
--- a/src/share/vm/runtime/arguments.cpp	Tue Sep 05 22:26:00 2017 +0200
+++ b/src/share/vm/runtime/arguments.cpp	Wed Sep 06 16:17:43 2017 +0200
@@ -2083,12 +2083,6 @@
   if (FLAG_IS_DEFAULT(UseBiasedLocking)) {
     FLAG_SET_DEFAULT(UseBiasedLocking, false);
   }
-
-  // Default System.gc() means full stop-the-world GC, which might surprise users.
-  // Replace it with full concurrent GC, unless user really wants otherwise.
-  if (FLAG_IS_DEFAULT(ExplicitGCInvokesConcurrent)) {
-    FLAG_SET_DEFAULT(ExplicitGCInvokesConcurrent, true);
-  }
 }

 void Arguments::set_gc_specific_flags() {
diff -r 096345a40169 test/gc/shenandoah/options/TestExplicitGC.java
--- a/test/gc/shenandoah/options/TestExplicitGC.java	Tue Sep 05 22:26:00 2017 +0200
+++ b/test/gc/shenandoah/options/TestExplicitGC.java	Wed Sep 06 16:17:43 2017 +0200
@@ -57,8 +57,8 @@
                                     TestExplicitGC.class.getName(),
                                     "test");
             OutputAnalyzer output = new OutputAnalyzer(pb.start());
-            output.shouldNotContain("Pause Full");
-            output.shouldContain("Pause Init Mark");
+            output.shouldContain("Pause Full");
+            output.shouldNotContain("Pause Init Mark");
         }

         {


Thanks,
-Aleksey