--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/gc/shared/referencePendingListLocker.hpp	Thu Mar 17 08:07:53 2016 +0100
@@ -0,0 +1,95 @@
+/*
+ * Copyright (c) 2016, 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.
+ *
+ */
+
+#ifndef SHARE_VM_GC_SHARED_REFERENCEPENDINGLISTLOCKER_HPP
+#define SHARE_VM_GC_SHARED_REFERENCEPENDINGLISTLOCKER_HPP
+
+#include "memory/allocation.hpp"
+#include "runtime/basicLock.hpp"
+#include "runtime/mutex.hpp"
+#include "runtime/thread.hpp"
+#include "utilities/exceptions.hpp"
+
+//
+// The ReferencePendingListLockerThread locks and unlocks the reference
+// pending list lock on behalf a non-Java thread, typically a concurrent
+// GC thread. This interface should not be directly accessed. All uses
+// should instead go through the ReferencePendingListLocker, which calls
+// this thread if needed.
+//
+class ReferencePendingListLockerThread : public JavaThread {
+private:
+  enum Message {
+    NONE,
+    LOCK,
+    UNLOCK
+  };
+
+  Monitor _monitor;
+  Message _message;
+
+  ReferencePendingListLockerThread();
+
+  static void start(JavaThread* thread, TRAPS);
+
+  void send_message(Message message);
+  void receive_and_handle_messages();
+
+public:
+  static ReferencePendingListLockerThread* create(TRAPS);
+
+  virtual bool is_hidden_from_external_view() const;
+
+  void lock();
+  void unlock();
+};
+
+//
+// The ReferencePendingListLocker is the main interface for locking and
+// unlocking the reference pending list lock, which needs to be held by
+// the GC when adding references to the pending list. Since this is a
+// Java-level monitor it can only be locked/unlocked by a Java thread.
+// For this reason there is an option to spawn a helper thread, the
+// ReferencePendingListLockerThread, during initialization. If a helper
+// thread is spawned all lock operations from non-Java threads will be
+// delegated to the helper thread. The helper thread is typically needed
+// by concurrent GCs.
+//
+class ReferencePendingListLocker VALUE_OBJ_CLASS_SPEC {
+private:
+  static bool                              _is_initialized;
+  static ReferencePendingListLockerThread* _locker_thread;
+  BasicLock                                _basic_lock;
+
+public:
+  static void initialize(bool needs_locker_thread, TRAPS);
+  static bool is_initialized();
+
+  static bool is_locked_by_self();
+
+  void lock();
+  void unlock();
+};
+
+#endif // SHARE_VM_GC_SHARED_REFERENCEPENDINGLISTLOCKER_HPP