--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdEpoch.hpp	Tue May 15 20:24:34 2018 +0200
@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2016, 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.
+ *
+ */
+
+#ifndef SHARE_VM_JFR_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDEPOCH_HPP
+#define SHARE_VM_JFR_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDEPOCH_HPP
+
+#include "memory/allocation.hpp"
+#include "jfr/utilities/jfrTypes.hpp"
+
+#define USED_BIT 1
+#define METHOD_USED_BIT (USED_BIT << 2)
+#define EPOCH_1_SHIFT 0
+#define EPOCH_2_SHIFT 1
+#define LEAKP_SHIFT 8
+
+#define USED_EPOCH_1_BIT (USED_BIT << EPOCH_1_SHIFT)
+#define USED_EPOCH_2_BIT (USED_BIT << EPOCH_2_SHIFT)
+#define LEAKP_USED_EPOCH_1_BIT (USED_EPOCH_1_BIT << LEAKP_SHIFT)
+#define LEAKP_USED_EPOCH_2_BIT (USED_EPOCH_2_BIT << LEAKP_SHIFT)
+#define METHOD_USED_EPOCH_1_BIT (METHOD_USED_BIT << EPOCH_1_SHIFT)
+#define METHOD_USED_EPOCH_2_BIT (METHOD_USED_BIT << EPOCH_2_SHIFT)
+#define METHOD_AND_CLASS_IN_USE_BITS (METHOD_USED_BIT | USED_BIT)
+#define METHOD_AND_CLASS_IN_USE_EPOCH_1_BITS (METHOD_AND_CLASS_IN_USE_BITS << EPOCH_1_SHIFT)
+#define METHOD_AND_CLASS_IN_USE_EPOCH_2_BITS (METHOD_AND_CLASS_IN_USE_BITS << EPOCH_2_SHIFT)
+
+class JfrTraceIdEpoch : AllStatic {
+  friend class JfrCheckpointManager;
+ private:
+  static bool _epoch_state;
+  static void shift_epoch();
+
+ public:
+  static bool epoch() {
+    return _epoch_state;
+  }
+
+  static jlong epoch_address() {
+    return (jlong)&_epoch_state;
+  }
+
+  static u1 current() {
+    return _epoch_state ? (u1)1 : (u1)0;
+  }
+
+  static u1 previous() {
+    return _epoch_state ? (u1)0 : (u1)1;
+  }
+
+  static traceid in_use_this_epoch_bit() {
+    return _epoch_state ? USED_EPOCH_2_BIT : USED_EPOCH_1_BIT;
+  }
+
+  static traceid in_use_prev_epoch_bit() {
+    return _epoch_state ? USED_EPOCH_1_BIT : USED_EPOCH_2_BIT;
+  }
+
+  static traceid leakp_in_use_this_epoch_bit() {
+    return _epoch_state ? LEAKP_USED_EPOCH_2_BIT : LEAKP_USED_EPOCH_1_BIT;
+  }
+
+  static traceid leakp_in_use_prev_epoch_bit() {
+    return _epoch_state ? LEAKP_USED_EPOCH_1_BIT : LEAKP_USED_EPOCH_2_BIT;
+  }
+
+  static traceid method_in_use_this_epoch_bit() {
+    return _epoch_state ? METHOD_USED_EPOCH_2_BIT : METHOD_USED_EPOCH_1_BIT;
+  }
+
+  static traceid method_in_use_prev_epoch_bit() {
+    return _epoch_state ? METHOD_USED_EPOCH_1_BIT : METHOD_USED_EPOCH_2_BIT;
+  }
+
+  static traceid method_and_class_in_use_this_epoch_bits() {
+    return _epoch_state ? METHOD_AND_CLASS_IN_USE_EPOCH_2_BITS : METHOD_AND_CLASS_IN_USE_EPOCH_1_BITS;
+  }
+
+  static traceid method_and_class_in_use_prev_epoch_bits() {
+    return _epoch_state ? METHOD_AND_CLASS_IN_USE_EPOCH_1_BITS :  METHOD_AND_CLASS_IN_USE_EPOCH_2_BITS;
+  }
+};
+
+#endif // SHARE_VM_JFR_CHECKPOINT_TYPES_TRACEID_JFRTRACEIDEPOCH_HPP