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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.net.nntp;
19  
20  /**
21   * A placeholder utility class, used for constructing a tree of Threadables
22   * Original implementation by Jamie Zawinski.
23   * See the Grendel source for more details <a href="http://lxr.mozilla.org/mozilla/source/grendel/sources/grendel/view/Threader.java#511">here</a>
24   * Threadable objects
25   * @author Rory Winston <rwinston@apache.org>
26   */
27  class ThreadContainer {
28      Threadable threadable;
29      ThreadContainer parent;
30  //    ThreadContainer prev;
31      ThreadContainer next;
32      ThreadContainer child;
33  
34      /**
35       *
36       * @param container
37       * @return true if child is under self's tree. Detects circular references
38       */
39      boolean findChild(ThreadContainer target) {
40          if (child == null) {
41              return false;
42          } else if (child == target) {
43              return true;
44          } else {
45              return child.findChild(target);
46          }
47      }
48  
49      // Copy the ThreadContainer tree structure down into the underlying Threadable objects
50      // (Make the Threadable tree look like the ThreadContainer tree)
51      // TODO convert this to an iterative function - this can blow the stack
52      // with very large Threadable trees
53      void flush() {
54          if (parent != null && threadable == null) {
55              throw new RuntimeException("no threadable in " + this.toString());
56          }
57  
58          parent = null;
59  
60          if (threadable != null) {
61              threadable.setChild(child == null ? null : child.threadable);
62          }
63  
64          if (child != null) {
65              child.flush();
66              child = null;
67          }
68  
69          if (threadable != null) {
70              threadable.setNext(next == null ? null : next.threadable);
71          }
72  
73          if (next != null) {
74              next.flush();
75              next = null;
76          }
77  
78          threadable = null;
79      }
80  
81      /**
82       * Reverse the entire set of children
83       *
84       */
85      void reverseChildren() {
86          if (child != null) {
87              ThreadContainer kid, prev, rest;
88              for (prev = null, kid = child, rest = kid.next;
89                  kid != null;
90                  prev = kid,
91                      kid = rest,
92                      rest = (rest == null ? null : rest.next))
93              {
94                  kid.next = prev;
95              }
96  
97              child = prev;
98  
99              // Do it for the kids
100             for (kid = child; kid != null; kid = kid.next) {
101                 kid.reverseChildren();
102             }
103         }
104     }
105 }