diff -r 8b6cc0bb93d0 -r 9186be5c78ba src/hotspot/share/gc/shenandoah/shenandoahLock.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/gc/shenandoah/shenandoahLock.cpp	Wed Nov 27 11:52:57 2019 -0500
@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2019, Red Hat, Inc. All rights reserved.
+ *
+ * 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 "runtime/os.hpp"
+
+#include "gc/shenandoah/shenandoahLock.hpp"
+#include "runtime/atomic.hpp"
+#include "runtime/os.inline.hpp"
+#include "runtime/thread.hpp"
+
+ShenandoahSimpleLock::ShenandoahSimpleLock() {
+  assert(os::mutex_init_done(), "Too early!");
+}
+
+void ShenandoahSimpleLock::lock() {
+  _lock.lock();
+}
+
+void ShenandoahSimpleLock::unlock() {
+  _lock.unlock();
+}
+
+ShenandoahReentrantLock::ShenandoahReentrantLock() :
+  ShenandoahSimpleLock(), _owner(NULL), _count(0) {
+  assert(os::mutex_init_done(), "Too early!");
+}
+
+ShenandoahReentrantLock::~ShenandoahReentrantLock() {
+  assert(_count == 0, "Unbalance");
+}
+
+void ShenandoahReentrantLock::lock() {
+  Thread* const thread = Thread::current();
+  Thread* const owner = Atomic::load(&_owner);
+
+  if (owner != thread) {
+    ShenandoahSimpleLock::lock();
+    Atomic::store(&_owner, thread);
+  }
+
+  _count++;
+}
+
+void ShenandoahReentrantLock::unlock() {
+  assert(owned_by_self(), "Invalid owner");
+  assert(_count > 0, "Invalid count");
+
+  _count--;
+
+  if (_count == 0) {
+    Atomic::store(&_owner, (Thread*)NULL);
+    ShenandoahSimpleLock::unlock();
+  }
+}
+
+bool ShenandoahReentrantLock::owned_by_self() const {
+  Thread* const thread = Thread::current();
+  Thread* const owner = Atomic::load(&_owner);
+  return owner == thread;
+}