--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/jfr/utilities/jfrDoublyLinkedList.hpp	Tue May 15 20:24:34 2018 +0200
@@ -0,0 +1,218 @@
+/*
+ * 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_JFRDOUBLYLINKEDLIST_HPP
+#define SHARE_VM_JFR_UTILITIES_JFRDOUBLYLINKEDLIST_HPP
+
+#include "memory/allocation.hpp"
+
+template <typename T>
+class JfrDoublyLinkedList {
+ private:
+  T* _head;
+  T* _tail;
+  size_t _count;
+
+  T** list_head() { return &_head; }
+  T** list_tail() { return &_tail; }
+
+ public:
+  typedef T Node;
+  JfrDoublyLinkedList() : _head(NULL), _tail(NULL), _count(0) {}
+  T* head() const { return _head; }
+  T* tail() const { return _tail; }
+  size_t count() const { return _count; }
+  T* clear(bool return_tail = false);
+  T* remove(T* const node);
+  void prepend(T* const node);
+  void append(T* const node);
+  void append_list(T* const head_node, T* const tail_node, size_t count);
+  debug_only(bool in_list(const T* const target_node) const;)
+  debug_only(bool locate(const T* start_node, const T* const target_node) const;)
+};
+
+template <typename T>
+inline void JfrDoublyLinkedList<T>::prepend(T* const node) {
+  assert(node != NULL, "invariant");
+  node->set_prev(NULL);
+  assert(!in_list(node), "already in list error");
+  T** lh = list_head();
+  if (*lh != NULL) {
+    (*lh)->set_prev(node);
+    node->set_next(*lh);
+  } else {
+    T** lt = list_tail();
+    assert(*lt == NULL, "invariant");
+    *lt = node;
+    node->set_next(NULL);
+    assert(tail() == node, "invariant");
+    assert(node->next() == NULL, "invariant");
+  }
+  *lh = node;
+  ++_count;
+  assert(head() == node, "head error");
+  assert(in_list(node), "not in list error");
+  assert(node->prev() == NULL, "invariant");
+}
+
+template <typename T>
+void JfrDoublyLinkedList<T>::append(T* const node) {
+  assert(node != NULL, "invariant");
+  node->set_next(NULL);
+  assert(!in_list(node), "already in list error");
+  T** lt = list_tail();
+  if (*lt != NULL) {
+    // already an existing tail
+    node->set_prev(*lt);
+    (*lt)->set_next(node);
+  } else {
+    // if no tail, also update head
+    assert(*lt == NULL, "invariant");
+    T** lh = list_head();
+    assert(*lh == NULL, "invariant");
+    node->set_prev(NULL);
+    *lh = node;
+    assert(head() == node, "invariant");
+  }
+  *lt = node;
+  ++_count;
+  assert(tail() == node, "invariant");
+  assert(in_list(node), "not in list error");
+  assert(node->next() == NULL, "invariant");
+}
+
+template <typename T>
+T* JfrDoublyLinkedList<T>::remove(T* const node) {
+  assert(node != NULL, "invariant");
+  assert(in_list(node), "invariant");
+  T* const prev = (T*)node->prev();
+  T* const next = (T*)node->next();
+  if (prev == NULL) {
+    assert(head() == node, "head error");
+    if (next != NULL) {
+      next->set_prev(NULL);
+    } else {
+      assert(next == NULL, "invariant");
+      assert(tail() == node, "tail error");
+      T** lt = list_tail();
+      *lt = NULL;
+      assert(tail() == NULL, "invariant");
+    }
+    T** lh = list_head();
+    *lh = next;
+    assert(head() == next, "invariant");
+  } else {
+    assert(prev != NULL, "invariant");
+    if (next == NULL) {
+      assert(tail() == node, "tail error");
+      T** lt = list_tail();
+      *lt = prev;
+      assert(tail() == prev, "invariant");
+    } else {
+       next->set_prev(prev);
+    }
+    prev->set_next(next);
+  }
+  --_count;
+  assert(_count >= 0, "invariant");
+  assert(!in_list(node), "still in list error");
+  return node;
+}
+
+template <typename T>
+T* JfrDoublyLinkedList<T>::clear(bool return_tail /* false */) {
+  T* const node = return_tail ? tail() : head();
+  T** l = list_head();
+  *l = NULL;
+  l = list_tail();
+  *l = NULL;
+  _count = 0;
+  assert(head() == NULL, "invariant");
+  assert(tail() == NULL, "invariant");
+  return node;
+}
+
+#ifdef ASSERT
+template <typename T>
+bool JfrDoublyLinkedList<T>::locate(const T* node, const T* const target) const {
+  assert(target != NULL, "invariant");
+  while (node != NULL) {
+    if (node == target) {
+      return true;
+    }
+    node = (T*)node->next();
+  }
+  return false;
+}
+
+template <typename T>
+bool JfrDoublyLinkedList<T>::in_list(const T* const target) const {
+  assert(target != NULL, "invariant");
+  return locate(head(), target);
+}
+
+template <typename T>
+inline void validate_count_param(T* node, size_t count_param) {
+  assert(node != NULL, "invariant");
+  size_t count = 0;
+  while (node) {
+    ++count;
+    node = (T*)node->next();
+  }
+  assert(count_param == count, "invariant");
+}
+#endif // ASSERT
+
+template <typename T>
+void JfrDoublyLinkedList<T>::append_list(T* const head_node, T* const tail_node, size_t count) {
+  assert(head_node != NULL, "invariant");
+  assert(!in_list(head_node), "already in list error");
+  assert(tail_node != NULL, "invariant");
+  assert(!in_list(tail_node), "already in list error");
+  assert(tail_node->next() == NULL, "invariant");
+  // ensure passed in list nodes are connected
+  assert(locate(head_node, tail_node), "invariant");
+  T** lt = list_tail();
+  if (*lt != NULL) {
+    head_node->set_prev(*lt);
+    (*lt)->set_next(head_node);
+  } else {
+    // no head
+    assert(*lt == NULL, "invariant");
+    T** lh = list_head();
+    assert(*lh == NULL, "invariant");
+    head_node->set_prev(NULL);
+    *lh = head_node;
+    assert(head() == head_node, "invariant");
+  }
+  *lt = tail_node;
+  const T* node = head_node;
+  debug_only(validate_count_param(node, count);)
+    _count += count;
+  assert(tail() == tail_node, "invariant");
+  assert(in_list(tail_node), "not in list error");
+  assert(in_list(head_node), "not in list error");
+}
+
+#endif // SHARE_VM_JFR_UTILITIES_JFRDOUBLYLINKEDLIST_HPP