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diff --git a/runtime/monitor_pool.h b/runtime/monitor_pool.h
new file mode 100644
index 0000000000..32f3f4ebe3
--- /dev/null
+++ b/runtime/monitor_pool.h
@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ART_RUNTIME_MONITOR_POOL_H_
+#define ART_RUNTIME_MONITOR_POOL_H_
+
+#include "monitor.h"
+
+#include "safe_map.h"
+
+#include <stdint.h>
+
+namespace art {
+
+// Abstraction to keep monitors small enough to fit in a lock word (32bits). On 32bit systems the
+// monitor id loses the alignment bits of the Monitor*.
+class MonitorPool {
+ public:
+  static MonitorPool* Create() {
+#ifndef __LP64__
+    return nullptr;
+#else
+    return new MonitorPool();
+#endif
+  }
+
+  static Monitor* MonitorFromMonitorId(MonitorId mon_id) {
+#ifndef __LP64__
+    return reinterpret_cast<Monitor*>(mon_id << 3);
+#else
+    return Runtime::Current()->GetMonitorPool()->LookupMonitorFromTable(mon_id);
+#endif
+  }
+
+  static MonitorId MonitorIdFromMonitor(Monitor* mon) {
+#ifndef __LP64__
+    return reinterpret_cast<MonitorId>(mon) >> 3;
+#else
+    return mon->GetMonitorId();
+#endif
+  }
+
+  static MonitorId CreateMonitorId(Thread* self, Monitor* mon) {
+#ifndef __LP64__
+    UNUSED(self);
+    return MonitorIdFromMonitor(mon);
+#else
+    return Runtime::Current()->GetMonitorPool()->AllocMonitorIdFromTable(self, mon);
+#endif
+  }
+
+  static void ReleaseMonitorId(MonitorId mon_id) {
+#ifndef __LP64__
+    UNUSED(mon_id);
+#else
+    Runtime::Current()->GetMonitorPool()->ReleaseMonitorIdFromTable(mon_id);
+#endif
+  }
+
+ private:
+#ifdef __LP64__
+  MonitorPool();
+
+  Monitor* LookupMonitorFromTable(MonitorId mon_id);
+
+  MonitorId LookupMonitorIdFromTable(Monitor* mon);
+
+  MonitorId AllocMonitorIdFromTable(Thread* self, Monitor* mon);
+
+  void ReleaseMonitorIdFromTable(MonitorId mon_id);
+
+  ReaderWriterMutex allocated_ids_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
+  static constexpr uint32_t kMaxMonitorId = 0xFFFF;
+  std::bitset<kMaxMonitorId> allocated_ids_ GUARDED_BY(allocated_ids_lock_);
+  SafeMap<MonitorId, Monitor*> table_ GUARDED_BY(allocated_ids_lock_);
+#endif
+};
+
+}  // namespace art
+
+#endif  // ART_RUNTIME_MONITOR_POOL_H_