--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/jfr/utilities/jfrIterator.hpp	Tue May 15 20:24:34 2018 +0200
@@ -0,0 +1,107 @@
+/*
+ * 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_UTILITIES_JFRLISTITERATOR_HPP
+#define SHARE_VM_JFR_UTILITIES_JFRLISTITERATOR_HPP
+
+#include "memory/allocation.hpp"
+
+enum jfr_iter_direction {
+  forward = 1,
+  backward
+};
+
+template <typename Node>
+class StopOnNullCondition : public AllStatic {
+ public:
+  static bool has_next(const Node* node) {
+    return node != NULL;
+  }
+};
+
+template <typename List, template <typename> class ContinuationPredicate>
+class Navigator {
+ public:
+  typedef typename List::Node Node;
+  typedef jfr_iter_direction Direction;
+  Navigator(List& list, Direction direction) :
+    _list(list), _node(direction == forward ? list.head() : list.tail()), _direction(direction) {}
+  bool has_next() const {
+    return ContinuationPredicate<Node>::has_next(_node);
+  }
+
+  bool direction_forward() const {
+    return _direction == forward;
+  }
+
+  Node* next() const {
+    assert(_node != NULL, "invariant");
+    Node* temp = _node;
+    _node = direction_forward() ? (Node*)_node->next() : (Node*)_node->prev();
+    return temp;
+  }
+
+  void set_direction(Direction direction) {
+    _direction = direction;
+  }
+
+  void reset(Direction direction) {
+    set_direction(direction);
+    _node = direction_forward() ? _list.head() : _list.tail();
+  }
+
+ private:
+  List& _list;
+  mutable Node* _node;
+  Direction _direction;
+};
+
+template <typename List>
+class NavigatorStopOnNull : public Navigator<List, StopOnNullCondition> {
+ public:
+  NavigatorStopOnNull(List& list, jfr_iter_direction direction = forward) : Navigator<List, StopOnNullCondition>(list, direction) {}
+};
+
+template<typename List, template <typename> class Navigator, typename AP = StackObj>
+class IteratorHost : public AP {
+ private:
+  Navigator<List> _navigator;
+
+ public:
+  typedef typename List::Node Node;
+  typedef jfr_iter_direction Direction;
+  IteratorHost(List& list, Direction direction = forward) : AP(), _navigator(list, direction) {}
+  void reset(Direction direction = forward) { _navigator.reset(direction); }
+  bool has_next() const { return _navigator.has_next(); }
+  Node* next() const { return _navigator.next(); }
+  void set_direction(Direction direction) { _navigator.set_direction(direction); }
+};
+
+template<typename List, typename AP = StackObj>
+class StopOnNullIterator : public IteratorHost<List, NavigatorStopOnNull, AP> {
+ public:
+  StopOnNullIterator(List& list, jfr_iter_direction direction = forward) : IteratorHost<List, NavigatorStopOnNull, AP>(list, direction) {}
+};
+
+#endif // SHARE_VM_JFR_UTILITIES_JFRLISTITERATOR_HPP