--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/trace/tracingExport.cpp	Thu Apr 12 09:03:46 2018 -0400
@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2018, 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 "runtime/orderAccess.inline.hpp"
+#include "trace/tracingExport.hpp"
+
+// Allow lock-free reads of _sampler_thread.
+Thread* volatile TracingExport::_sampler_thread = NULL;
+
+Thread* TracingExport::sampler_thread_acquire() {
+  return (Thread*)OrderAccess::load_acquire(&_sampler_thread);
+}
+
+void TracingExport::set_sampler_thread_with_lock(Thread* thread) {
+  // Grab Threads_lock to avoid conflicts with Thread-SMR scans.
+  MutexLocker ml(Threads_lock);
+  assert(thread == NULL || _sampler_thread == NULL, "_sampler_thread should not already be set.");
+  // To match with the lock-free load_acquire():
+  OrderAccess::release_store(&_sampler_thread, thread);
+}