--- /dev/null	2016-03-09 14:43:31.591861332 +0100
+++ new/src/share/vm/gc/shared/referencePendingListLocker.cpp	2016-03-10 16:29:22.803104841 +0100
@@ -0,0 +1,226 @@
+/*
+ * 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.
+ *
+ */
+
+#include "precompiled.hpp"
+#include "classfile/javaClasses.hpp"
+#include "classfile/systemDictionary.hpp"
+#include "gc/shared/collectedHeap.hpp"
+#include "gc/shared/referencePendingListLocker.hpp"
+#include "memory/universe.hpp"
+#include "runtime/javaCalls.hpp"
+#include "utilities/preserveException.hpp"
+
+ReferencePendingListLockerThread::ReferencePendingListLockerThread() :
+  JavaThread(&start),
+  _monitor(Monitor::nonleaf, "ReferencePendingListLocker", false, Monitor::_safepoint_check_sometimes),
+  _message(NONE) {}
+
+ReferencePendingListLockerThread* ReferencePendingListLockerThread::create(TRAPS) {
+  // Create Java thread objects
+  instanceKlassHandle thread_klass = SystemDictionary::resolve_or_fail(vmSymbols::java_lang_Thread(), true, CHECK_NULL);
+  instanceHandle thread_object = thread_klass->allocate_instance_handle(CHECK_NULL);
+  Handle thread_name = java_lang_String::create_from_str("Reference Pending List Locker", CHECK_NULL);
+  Handle thread_group = Universe::system_thread_group();
+  JavaValue result(T_VOID);
+  JavaCalls::call_special(&result,
+                          thread_object,
+                          thread_klass,
+                          vmSymbols::object_initializer_name(),
+                          vmSymbols::threadgroup_string_void_signature(),
+                          thread_group,
+                          thread_name,
+                          CHECK_NULL);
+
+  {
+    MutexLocker ml(Threads_lock);
+
+    // Allocate thread
+    ReferencePendingListLockerThread* thread = new ReferencePendingListLockerThread();
+    if (thread == NULL || thread->osthread() == NULL) {
+      vm_exit_during_initialization("java.lang.OutOfMemoryError",
+                                    os::native_thread_creation_failed_msg());
+    }
+
+    // Initialize thread
+    java_lang_Thread::set_thread(thread_object(), thread);
+    java_lang_Thread::set_priority(thread_object(), NearMaxPriority);
+    java_lang_Thread::set_daemon(thread_object());
+    thread->set_threadObj(thread_object());
+
+    // Start thread
+    Threads::add(thread);
+    Thread::start(thread);
+
+    return thread;
+  }
+}
+
+void ReferencePendingListLockerThread::start(JavaThread* thread, TRAPS) {
+  ReferencePendingListLockerThread* locker_thread = static_cast<ReferencePendingListLockerThread*>(thread);
+  locker_thread->receive_and_handle_messages();
+}
+
+bool ReferencePendingListLockerThread::is_hidden_from_external_view() const {
+  return true;
+}
+
+void ReferencePendingListLockerThread::send_message(Message message) {
+  assert(message != NONE, "Should not be none");
+  MonitorLockerEx ml(&_monitor, Monitor::_no_safepoint_check_flag);
+
+  // Wait for completion of current message
+  while (_message != NONE) {
+    ml.wait(Monitor::_no_safepoint_check_flag);
+  }
+
+  // Send new message
+  _message = message;
+  ml.notify_all();
+
+  // Wait for completion of new message
+  while (_message != NONE) {
+    ml.wait(Monitor::_no_safepoint_check_flag);
+  }
+}
+
+void ReferencePendingListLockerThread::receive_and_handle_messages() {
+  ReferencePendingListLocker pending_list_locker;
+  MonitorLockerEx ml(&_monitor);
+
+  // Main loop, never terminates
+  for (;;) {
+    // Wait for message
+    while (_message == NONE) {
+      ml.wait();
+    }
+
+    // Handle message
+    if (_message == LOCK) {
+      pending_list_locker.lock();
+    } else if (_message == UNLOCK) {
+      pending_list_locker.unlock();
+    } else {
+      ShouldNotReachHere();
+    }
+
+    // Clear message
+    _message = NONE;
+    ml.notify_all();
+  }
+}
+
+void ReferencePendingListLockerThread::lock() {
+  send_message(LOCK);
+}
+
+void ReferencePendingListLockerThread::unlock() {
+  send_message(UNLOCK);
+}
+
+bool ReferencePendingListLocker::_is_initialized = false;
+ReferencePendingListLockerThread* ReferencePendingListLocker::_locker_thread = NULL;
+
+void ReferencePendingListLocker::initialize(bool needs_locker_thread, TRAPS) {
+  if (needs_locker_thread) {
+    _locker_thread = ReferencePendingListLockerThread::create(CHECK);
+  }
+
+  _is_initialized = true;
+}
+
+bool ReferencePendingListLocker::is_initialized() {
+  return _is_initialized;
+}
+
+bool ReferencePendingListLocker::is_locked_by_self() {
+  oop pending_list_lock = java_lang_ref_Reference::pending_list_lock();
+  if (pending_list_lock == NULL) {
+    return false;
+  }
+
+  JavaThread* thread = JavaThread::current();
+  Handle handle(thread, pending_list_lock);
+  return ObjectSynchronizer::current_thread_holds_lock(thread, handle);
+}
+
+void ReferencePendingListLocker::lock() {
+  assert(!Heap_lock->owned_by_self(), "Heap_lock must not be owned by requesting thread");
+
+  if (Thread::current()->is_Java_thread()) {
+    assert(java_lang_ref_Reference::pending_list_lock() != NULL, "Not initialized");
+
+    // We may enter this with a pending exception
+    PRESERVE_EXCEPTION_MARK;
+
+    HandleMark hm;
+    Handle handle(THREAD, java_lang_ref_Reference::pending_list_lock());
+
+    assert(!is_locked_by_self(), "Should not be locked by self");
+
+    // Lock
+    ObjectSynchronizer::fast_enter(handle, &_basic_lock, false, THREAD);
+
+    assert(is_locked_by_self(), "Locking failed");
+
+    if (HAS_PENDING_EXCEPTION) {
+      CLEAR_PENDING_EXCEPTION;
+    }
+  } else {
+    // Delegate operation to locker thread
+    assert(_locker_thread != NULL, "Locker thread not created");
+    _locker_thread->lock();
+  }
+}
+
+void ReferencePendingListLocker::unlock() {
+  if (Thread::current()->is_Java_thread()) {
+    assert(java_lang_ref_Reference::pending_list_lock() != NULL, "Not initialized");
+
+    // We may enter this with a pending exception
+    PRESERVE_EXCEPTION_MARK;
+
+    HandleMark hm;
+    Handle handle(THREAD, java_lang_ref_Reference::pending_list_lock());
+
+    assert(is_locked_by_self(), "Should be locked by self");
+
+    // Notify waiters if the pending list is non-empty
+    if (java_lang_ref_Reference::pending_list() != NULL) {
+      ObjectSynchronizer::notifyall(handle, THREAD);
+    }
+
+    // Unlock
+    ObjectSynchronizer::fast_exit(handle(), &_basic_lock, THREAD);
+
+    assert(!is_locked_by_self(), "Unlocking failed");
+
+    if (HAS_PENDING_EXCEPTION) {
+      CLEAR_PENDING_EXCEPTION;
+    }
+  } else {
+    // Delegate operation to locker thread
+    assert(_locker_thread != NULL, "Locker thread not created");
+    _locker_thread->unlock();
+  }
+}