--- /dev/null	2019-01-28 17:48:33.000000000 +0800
+++ new/src/share/vm/jfr/writers/jfrPosition.hpp	2019-01-28 17:48:33.000000000 +0800
@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2016, 2019, 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_WRITERS_JFRPOSITION_HPP
+#define SHARE_VM_JFR_WRITERS_JFRPOSITION_HPP
+
+#include "utilities/debug.hpp"
+#include "utilities/globalDefinitions.hpp"
+
+template <typename AP> // AllocationPolicy
+class Position : public AP {
+ private:
+  const u1* _start_pos; // logical start
+  u1* _current_pos;
+  const u1* _end_pos;
+
+ protected:
+  const u1* start_pos() const;
+  void set_start_pos(const u1* position);
+  u1* current_pos();
+  void set_current_pos(const u1* new_position);
+  void set_current_pos(size_t size);
+  const u1* end_pos() const;
+  void set_end_pos(const u1* position);
+  Position(const u1* start_pos, size_t size);
+  Position();
+
+ public:
+  size_t available_size() const;
+  intptr_t used_offset() const;
+  intptr_t current_offset() const;
+  size_t used_size() const;
+  void reset();
+};
+
+#endif // SHARE_VM_JFR_WRITERS_JFRPOSITION_HPP