--- /dev/null	2018-11-30 10:10:44.238550338 +0100
+++ new/src/hotspot/share/gc/shenandoah/shenandoahHeapLock.hpp	2018-11-30 10:23:48.235773289 +0100
@@ -0,0 +1,93 @@
+/*
+ * Copyright (c) 2017, 2018, 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.
+ *
+ */
+
+#ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP
+#define SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP
+
+#include "memory/allocation.hpp"
+#include "runtime/thread.hpp"
+
+class ShenandoahHeapLock  {
+private:
+  enum LockState { unlocked = 0, locked = 1 };
+
+  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile int));
+  volatile int _state;
+  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, sizeof(volatile Thread*));
+  volatile Thread* _owner;
+  DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, 0);
+
+public:
+  ShenandoahHeapLock() : _state(unlocked), _owner(NULL) {};
+
+  void lock() {
+    Thread::SpinAcquire(&_state, "Shenandoah Heap Lock");
+#ifdef ASSERT
+    assert(_state == locked, "must be locked");
+    assert(_owner == NULL, "must not be owned");
+    _owner = Thread::current();
+#endif
+  }
+
+  void unlock() {
+#ifdef ASSERT
+    assert (_owner == Thread::current(), "sanity");
+    _owner = NULL;
+#endif
+    Thread::SpinRelease(&_state);
+  }
+
+#ifdef ASSERT
+  void assert_owned_by_current_thread() {
+    assert(_state == locked, "must be locked");
+    assert(_owner == Thread::current(), "must be owned by current thread");
+  }
+
+  void assert_not_owned_by_current_thread() {
+    assert(_owner != Thread::current(), "must be not owned by current thread");
+  }
+
+  void assert_owned_by_current_thread_or_safepoint() {
+    Thread* thr = Thread::current();
+    assert((_state == locked && _owner == thr) ||
+           (SafepointSynchronize::is_at_safepoint() && thr->is_VM_thread()),
+           "must own heap lock or by VM thread at safepoint");
+  }
+#endif
+};
+
+class ShenandoahHeapLocker : public StackObj {
+private:
+  ShenandoahHeapLock* _lock;
+public:
+  ShenandoahHeapLocker(ShenandoahHeapLock* lock) {
+    _lock = lock;
+    _lock->lock();
+  }
+
+  ~ShenandoahHeapLocker() {
+    _lock->unlock();
+  }
+};
+
+#endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHHEAPLOCK_HPP