1 /*
   2  * Copyright (c) 2016, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_JFR_UTILITIES_JFRLISTITERATOR_HPP
  26 #define SHARE_VM_JFR_UTILITIES_JFRLISTITERATOR_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 
  30 enum jfr_iter_direction {
  31   forward = 1,
  32   backward
  33 };
  34 
  35 template <typename Node>
  36 class StopOnNullCondition : public AllStatic {
  37  public:
  38   static bool has_next(const Node* node) {
  39     return node != NULL;
  40   }
  41 };
  42 
  43 template <typename List, template <typename> class ContinuationPredicate>
  44 class Navigator {
  45  public:
  46   typedef typename List::Node Node;
  47   typedef jfr_iter_direction Direction;
  48   Navigator(List& list, Direction direction) :
  49     _list(list), _node(direction == forward ? list.head() : list.tail()), _direction(direction) {}
  50   bool has_next() const {
  51     return ContinuationPredicate<Node>::has_next(_node);
  52   }
  53 
  54   bool direction_forward() const {
  55     return _direction == forward;
  56   }
  57 
  58   Node* next() const {
  59     assert(_node != NULL, "invariant");
  60     Node* temp = _node;
  61     _node = direction_forward() ? (Node*)_node->next() : (Node*)_node->prev();
  62     return temp;
  63   }
  64 
  65   void set_direction(Direction direction) {
  66     _direction = direction;
  67   }
  68 
  69   void reset(Direction direction) {
  70     set_direction(direction);
  71     _node = direction_forward() ? _list.head() : _list.tail();
  72   }
  73 
  74  private:
  75   List& _list;
  76   mutable Node* _node;
  77   Direction _direction;
  78 };
  79 
  80 template <typename List>
  81 class NavigatorStopOnNull : public Navigator<List, StopOnNullCondition> {
  82  public:
  83   NavigatorStopOnNull(List& list, jfr_iter_direction direction = forward) : Navigator<List, StopOnNullCondition>(list, direction) {}
  84 };
  85 
  86 template<typename List, template <typename> class Navigator, typename AP = StackObj>
  87 class IteratorHost : public AP {
  88  private:
  89   Navigator<List> _navigator;
  90 
  91  public:
  92   typedef typename List::Node Node;
  93   typedef jfr_iter_direction Direction;
  94   IteratorHost(List& list, Direction direction = forward) : AP(), _navigator(list, direction) {}
  95   void reset(Direction direction = forward) { _navigator.reset(direction); }
  96   bool has_next() const { return _navigator.has_next(); }
  97   Node* next() const { return _navigator.next(); }
  98   void set_direction(Direction direction) { _navigator.set_direction(direction); }
  99 };
 100 
 101 template<typename List, typename AP = StackObj>
 102 class StopOnNullIterator : public IteratorHost<List, NavigatorStopOnNull, AP> {
 103  public:
 104   StopOnNullIterator(List& list, jfr_iter_direction direction = forward) : IteratorHost<List, NavigatorStopOnNull, AP>(list, direction) {}
 105 };
 106 
 107 #endif // SHARE_VM_JFR_UTILITIES_JFRLISTITERATOR_HPP