View Javadoc
1   //******************************************************************************
2   //
3   // File:    Spinner.java
4   // Package: edu.rit.pj
5   // Unit:    Class edu.rit.pj.Spinner
6   //
7   // This Java source file is copyright (C) 2007 by Alan Kaminsky. All rights
8   // reserved. For further information, contact the author, Alan Kaminsky, at
9   // ark@cs.rit.edu.
10  //
11  // This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
12  // software; you can redistribute it and/or modify it under the terms of the GNU
13  // General Public License as published by the Free Software Foundation; either
14  // version 3 of the License, or (at your option) any later version.
15  //
16  // PJ is distributed in the hope that it will be useful, but WITHOUT ANY
17  // WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
18  // A PARTICULAR PURPOSE. See the GNU General Public License for more details.
19  //
20  // Linking this library statically or dynamically with other modules is making a
21  // combined work based on this library. Thus, the terms and conditions of the GNU
22  // General Public License cover the whole combination.
23  //
24  // As a special exception, the copyright holders of this library give you
25  // permission to link this library with independent modules to produce an
26  // executable, regardless of the license terms of these independent modules, and
27  // to copy and distribute the resulting executable under terms of your choice,
28  // provided that you also meet, for each linked independent module, the terms
29  // and conditions of the license of that module. An independent module is a module
30  // which is not derived from or based on this library. If you modify this library,
31  // you may extend this exception to your version of the library, but you are not
32  // obligated to do so. If you do not wish to do so, delete this exception
33  // statement from your version.
34  //
35  // A copy of the GNU General Public License is provided in the file gpl.txt. You
36  // may also obtain a copy of the GNU General Public License on the World Wide
37  // Web at http://www.gnu.org/licenses/gpl.html.
38  //
39  //******************************************************************************
40  package edu.rit.pj;
41  
42  /**
43   * Class Spinner provides an object used to implement a spin-wait.
44   * <P>
45   * The pattern for coding a spin-wait is:
46   * <PRE>
47   *    if (&lt;condition&gt;)
48   *        {
49   *        Spinner spinner = new Spinner();
50   *        while (&lt;condition&gt;) spinner.spin();
51   *        }
52   * </PRE> This will wait as long as the <code>&lt;condition&gt;</code> is true.
53   *
54   * @author Alan Kaminsky
55   * @version 20-Dec-2007
56   */
57  class Spinner {
58  
59  // Hidden constants.
60      // In a spin-wait, the maximum number of iterations to spin before yielding
61      // the CPU.
62      static final int MAX_COUNT = 10000;
63  
64  // Hidden data members.
65      // Spin counter.
66      volatile int count;
67  
68      // 128 bytes of extra padding to avert cache interference.
69      private long p0, p1, p2, p3, p4, p5, p6, p7;
70      private long p8, p9, pa, pb, pc, pd, pe, pf;
71  
72  // Exported constructors.
73      /**
74       * Construct a new spinner.
75       */
76      public Spinner() {
77      }
78  
79  // Exported operations.
80      /**
81       * Spin this spinner. If enough consecutive <code>spin()</code> calls occur, the
82       * calling thread yields the CPU.
83       */
84      public void spin() {
85          if (count++ > MAX_COUNT) {
86              Thread.yield();
87              count = 0;
88          }
89      }
90  
91  }