Queue


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  package org.apache.catalina.util;
18  
19  import java.util.Vector  ;
20  
21  /**
22   * A simple FIFO queue class which causes the calling thread to wait
23   * if the queue is empty and notifies threads that are waiting when it
24   * is not empty.
25   *
26   * @author Anil V (akv@eng.sun.com)
27   */
28  public class Queue {
29      private Vector   vector = new Vector  ();
30  
31      /**
32       * Put the object into the queue.
33       *
34       * @param   object          the object to be appended to the
35       *                          queue.
36       */
37      public synchronized void put(Object   object) {
38          vector.addElement(object);
39          notify();
40      }
41  
42      /**
43       * Pull the first object out of the queue. Wait if the queue is
44       * empty.
45       */
46      public synchronized Object   pull() {
47          while (isEmpty())
48              try {
49                  wait();
50              } catch (InterruptedException   ex) {
51              }
52          return get();
53      }
54  
55      /**
56       * Get the first object out of the queue. Return null if the queue
57       * is empty.
58       */
59      public synchronized Object   get() {
60          Object   object = peek();
61          if (object != null)
62              vector.removeElementAt(0);
63          return object;
64      }
65  
66      /**
67       * Peek to see if something is available.
68       */
69      public Object   peek() {
70          if (isEmpty())
71              return null;
72          return vector.elementAt(0);
73      }
74  
75      /**
76       * Is the queue empty?
77       */
78      public boolean isEmpty() {
79          return vector.isEmpty();
80      }
81  
82      /**
83       * How many elements are there in this queue?
84       */
85      public int size() {
86          return vector.size();
87      }
88  }
89
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