FIFOWaitQueue


1   package org.apache.beehive.netui.util.internal.concurrent;
2   
3   import java.util.*;
4   
5   /**
6    * Simple linked list queue used in FIFOSemaphore.
7    * Methods are not synchronized; they depend on synch of callers.
8    * Must be public, since it is used by Semaphore (outside this package).
9    * NOTE: this class is NOT present in java.util.concurrent.
10   **/
11  
12  class FIFOWaitQueue extends WaitQueue implements java.io.Serializable   {
13      protected transient WaitNode head_ = null;
14      protected transient WaitNode tail_ = null;
15  
16      public FIFOWaitQueue() {}
17  
18      public void insert(WaitNode w) {
19          if (tail_ == null)
20              head_ = tail_ = w;
21          else {
22              tail_.next = w;
23              tail_ = w;
24          }
25      }
26  
27      public WaitNode extract() {
28          if (head_ == null)
29              return null;
30          else {
31              WaitNode w = head_;
32              head_ = w.next;
33              if (head_ == null)
34                  tail_ = null;
35              w.next = null;
36              return w;
37          }
38      }
39  
40      public boolean hasNodes() {
41          return head_ != null;
42      }
43  
44      public int getLength() {
45          int count = 0;
46          WaitNode node = head_;
47          while (node != null) {
48              if (node.waiting) count++;
49              node = node.next;
50          }
51          return count;
52      }
53  
54      public Collection getWaitingThreads() {
55          List list = new ArrayList();
56          int count = 0;
57          WaitNode node = head_;
58          while (node != null) {
59              if (node.waiting) list.add(node.owner);
60              node = node.next;
61          }
62          return list;
63      }
64  
65      public boolean isWaiting(Thread   thread) {
66          if (thread == null) throw new NullPointerException  ();
67          for (WaitNode node = head_; node != null; node = node.next) {
68              if (node.waiting && node.owner == thread) return true;
69          }
70          return false;
71      }
72  
73  }
74
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