--- a/.hgtags	Tue Apr 05 08:55:39 2016 -0700
+++ b/.hgtags	Mon Apr 11 14:58:21 2016 -0700
@@ -850,3 +850,4 @@
 d6c92b9e192ef97305a699e868387d55821c81ad jdk8u102-b00
 d6c92b9e192ef97305a699e868387d55821c81ad jdk8u82-b00
 516a64e6d7c2dc29fd932bf3b8313e560a01bcd0 jdk8u102-b01
+83dc7e55f71596e6e76fabfa56b6008e070ff44c jdk8u102-b02

--- a/src/share/vm/gc_implementation/g1/heapRegion.cpp	Tue Apr 05 08:55:39 2016 -0700
+++ b/src/share/vm/gc_implementation/g1/heapRegion.cpp	Mon Apr 11 14:58:21 2016 -0700
@@ -794,7 +794,9 @@
                                  "in region "HR_FORMAT,
                                  (void*) obj,
                                  HR_FORMAT_PARAMS(to));
-          obj->print_on(gclog_or_tty);
+          if (obj->is_oop()) {
+            obj->print_on(gclog_or_tty);
+          }
           gclog_or_tty->print_cr("Obj head CTE = %d, field CTE = %d.",
                         cv_obj, cv_field);
           gclog_or_tty->print_cr("----------");

--- a/src/share/vm/gc_implementation/shared/adaptiveSizePolicy.cpp	Tue Apr 05 08:55:39 2016 -0700
+++ b/src/share/vm/gc_implementation/shared/adaptiveSizePolicy.cpp	Mon Apr 11 14:58:21 2016 -0700
@@ -193,8 +193,9 @@
      (!FLAG_IS_DEFAULT(ParallelGCThreads) && !ForceDynamicNumberOfGCThreads)) {
     new_active_workers = total_workers;
   } else {
+    uintx min_workers = (total_workers == 1) ? 1 : 2;
     new_active_workers = calc_default_active_workers(total_workers,
-                                                     2, /* Minimum number of workers */
+                                                     min_workers,
                                                      active_workers,
                                                      application_workers);
   }

--- a/src/share/vm/runtime/arguments.cpp	Tue Apr 05 08:55:39 2016 -0700
+++ b/src/share/vm/runtime/arguments.cpp	Mon Apr 11 14:58:21 2016 -0700
@@ -1675,9 +1675,8 @@
   FLAG_SET_DEFAULT(ParallelGCThreads,
                      Abstract_VM_Version::parallel_worker_threads());
   if (ParallelGCThreads == 0) {
-    FLAG_SET_DEFAULT(ParallelGCThreads,
-                     Abstract_VM_Version::parallel_worker_threads());
-  }
+    vm_exit_during_initialization("The flag -XX:+UseG1GC can not be combined with -XX:ParallelGCThreads=0", NULL);
+    }
 
 #if INCLUDE_ALL_GCS
   if (G1ConcRefinementThreads == 0) {

--- a/test/TEST.groups	Tue Apr 05 08:55:39 2016 -0700
+++ b/test/TEST.groups	Mon Apr 11 14:58:21 2016 -0700
@@ -61,7 +61,6 @@
 # can be resolved in some cases by using tools from the compile-jdk.
 #
 needs_jdk = \
-  gc/TestG1ZeroPGCTJcmdThreadPrint.java \
   gc/metaspace/CompressedClassSpaceSizeInJmapHeap.java \
   gc/metaspace/TestMetaspacePerfCounters.java \
   gc/metaspace/TestPerfCountersAndMemoryPools.java \
@@ -216,6 +215,7 @@
   runtime/NMT \
   gc/class_unloading/TestCMSClassUnloadingEnabledHWM.java \
   gc/class_unloading/TestG1ClassUnloadingHWM.java \
+  gc/ergonomics/TestDynamicNumberOfGCThreads.java \
   gc/g1/TestRegionAlignment.java \
   gc/g1/TestShrinkToOneRegion.java \
   gc/metaspace/G1AddMetaspaceDependency.java \

--- a/test/gc/8000311/Test8000311.java	Tue Apr 05 08:55:39 2016 -0700
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,42 +0,0 @@
-/*
- * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/**
- * @test Test8000311
- * @key gc
- * @bug 8000311
- * @summary G1: ParallelGCThreads==0 broken
- * @run main/othervm -XX:+UseG1GC -XX:ParallelGCThreads=0 -XX:+ResizePLAB -XX:+ExplicitGCInvokesConcurrent Test8000311
- * @author filipp.zhinkin@oracle.com
- */
-
-import java.util.*;
-
-public class Test8000311 {
-  public static void main(String args[]) {
-    for(int i = 0; i<100; i++) {
-      byte[] garbage = new byte[1000];
-      System.gc();
-    }
-  }
-}

--- a/test/gc/TestG1ZeroPGCTJcmdThreadPrint.java	Tue Apr 05 08:55:39 2016 -0700
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,54 +0,0 @@
-/*
- * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
- * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
- *
- * This code is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 only, as
- * published by the Free Software Foundation.
- *
- * This code is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- * version 2 for more details (a copy is included in the LICENSE file that
- * accompanied this code).
- *
- * You should have received a copy of the GNU General Public License version
- * 2 along with this work; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
- *
- * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
- * or visit www.oracle.com if you need additional information or have any
- * questions.
- */
-
-/* @test TestG1ZeroPGCTJcmdThreadPrint
- * @key gc
- * @bug 8005875
- * @summary Use jcmd to generate a thread dump of a Java program being run with PGCT=0 to verify 8005875
- * @library /testlibrary
- * @run main/othervm -XX:+UseG1GC -XX:ParallelGCThreads=0 -XX:+IgnoreUnrecognizedVMOptions TestG1ZeroPGCTJcmdThreadPrint
- */
-
-import com.oracle.java.testlibrary.*;
-
-public class TestG1ZeroPGCTJcmdThreadPrint {
-  public static void main(String args[]) throws Exception {
-
-    // Grab the pid from the current java process
-    String pid = Integer.toString(ProcessTools.getProcessId());
-
-    // Create a ProcessBuilder
-    ProcessBuilder pb = new ProcessBuilder();
-
-    // Run jcmd <pid> Thread.print
-    pb.command(JDKToolFinder.getJDKTool("jcmd"), pid, "Thread.print");
-
-    OutputAnalyzer output = new OutputAnalyzer(pb.start());
-
-    // There shouldn't be a work gang for concurrent marking.
-    output.shouldNotContain("G1 Parallel Marking Threads");
-
-    // Make sure we didn't crash
-    output.shouldHaveExitValue(0);
-  }
-}

--- a/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java	Tue Apr 05 08:55:39 2016 -0700
+++ b/test/gc/ergonomics/TestDynamicNumberOfGCThreads.java	Mon Apr 11 14:58:21 2016 -0700
@@ -44,14 +44,24 @@
   }
 
   private static void verifyDynamicNumberOfGCThreads(OutputAnalyzer output) {
+    output.shouldHaveExitValue(0); // test should run succesfully
     output.shouldContain("new_active_workers");
-    output.shouldHaveExitValue(0);
   }
 
   private static void testDynamicNumberOfGCThreads(String gcFlag) throws Exception {
     // UseDynamicNumberOfGCThreads and TraceDynamicGCThreads enabled
-    ProcessBuilder pb_enabled =
-      ProcessTools.createJavaProcessBuilder("-XX:+" + gcFlag, "-Xmx10M", "-XX:+PrintGCDetails",  "-XX:+UseDynamicNumberOfGCThreads", "-XX:+TraceDynamicGCThreads", GCTest.class.getName());
+    String[] baseArgs = {"-XX:+" + gcFlag, "-Xmx10M", "-XX:+PrintGCDetails",  "-XX:+UseDynamicNumberOfGCThreads", "-XX:+TraceDynamicGCThreads", GCTest.class.getName()};
+
+    // Base test with gc and +UseDynamicNumberOfGCThreads:
+    ProcessBuilder pb_enabled = ProcessTools.createJavaProcessBuilder(baseArgs);
+    verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
+
+    // Ensure it also works on uniprocessors or if user specifies -XX:ParallelGCThreads=1:
+    String[] extraArgs = {"-XX:+UnlockDiagnosticVMOptions", "-XX:+ForceDynamicNumberOfGCThreads", "-XX:ParallelGCThreads=1"};
+    String[] finalArgs = new String[baseArgs.length + extraArgs.length];
+    System.arraycopy(extraArgs, 0, finalArgs, 0,                extraArgs.length);
+    System.arraycopy(baseArgs,  0, finalArgs, extraArgs.length, baseArgs.length);
+    pb_enabled = ProcessTools.createJavaProcessBuilder(finalArgs);
     verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
   }