JTREG help:
"Tests are not allowed to call System.exit because the test must have the ability to run in the same JVM as the harness. Calling System.exit while the test is running in this manner would cause the harness itself to exit! Instead of calling System.exit(), throw an exception."

After fix 8143081

--- a/test/testlibrary/ctw/src/sun/hotspot/tools/ctw/CompileTheWorld.java Mon Jun 27 17:23:15 2016 +0300
+++ b/test/testlibrary/ctw/src/sun/hotspot/tools/ctw/CompileTheWorld.java Tue Jun 28 19:58:15 2016 +0300
@@ -93,6 +89,9 @@
                 os.close();
             }
         }
+ // in case when a static constructor creates and runs a new thread
+ // we force it to exit
+ System.exit(0);
     }

System::exit used here by reason JDK-8159155: Loading the class "sun.tools.jconsole.OutputViewer" shows a modal dialog
The harness just hung and failed with timeout.