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Java > Open Source Codes > org > prevayler > foundation > Turn


1 package org.prevayler.foundation;
2
3
4 /** Used to sequence operations that have to be performed in order by several concurrent threads.
5  */
6 public class Turn {
7
8     private Turn _next;
9     private int _tickets = 0;
10     private boolean _isAlwaysSkipped;
11
12
13     public static Turn first() { return new Turn(1000000); } //Arbitrarily large number.
14
15     private Turn(int tickets) { _tickets = tickets; }
16
17     public Turn next() {
18         if (_next == null) _next = new Turn(0);
19         return _next;
20     }
21
22     public synchronized void start() {
23         if (_tickets == 0) Cool.wait(this);
24         _tickets--;
25     }
26
27     public void end() {
28         next().haveSomeTickets(1);
29     }
30     
31     private synchronized void haveSomeTickets(int tickets) {
32         if (_isAlwaysSkipped) {
33             next().haveSomeTickets(tickets);
34             return;
35         }
36         _tickets += tickets;
37         notify();
38     }
39
40     public synchronized void alwaysSkip() {
41         end();
42         _isAlwaysSkipped = true;
43         next().haveSomeTickets(_tickets);
44     }
45
46 }
47
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