Yurttas/PL/OOL/Java/F/07/04/RWMonitor.java

 1/**
 2 *  Copyright(C) 1998
 3 *  All Rights Reserved. Salih Yurttas, ZCubes, BitsOfCode Software Systems, Inc..
 4 *
 5 *  Permission to use, copy, modify, and distribute this
 6 *  software and its documentation for EDUCATIONAL purposes
 7 *  and without fee is hereby granted provided that this
 8 *  copyright notice appears in all copies.
 9 *
10 *  @date   : January 1, 1998.
11 *  @author : Salih Yurttas.
12 */
13
14
15public class RWMonitor {
16
17  private int nReaders=0;
18  private int nWriters=0;
19
20  private ReadWriteMutex readerMutex = new ReadWriteMutex();
21  private ReadWriteMutex writerMutex = new ReadWriteMutex();
22
23  private synchronized boolean readable() {
24    if(nWriters>0)
25      return false; 
26
27    nReaders++;
28
29    return true;
30  }
31
32  private synchronized boolean writable() {
33    nWriters++;
34
35    if(nWriters>1)
36      return false;
37
38    if(nReaders>0)
39      return false;
40
41    return true;
42  }
43
44  public void startRead(){
45    while(!readable()){
46      try {
47        readerMutex.mutWait();
48      }
49      catch(InterruptedException iE) {}
50    }
51  }
52
53  public synchronized void endRead() {
54    nReaders--;
55
56    if(nReaders==0)
57      if(nWriters>0)
58        writerMutex.mutNotify();
59  }
60
61  public void startWrite() {
62    if(!writable())
63      try {
64        writerMutex.mutWait();
65      }
66      catch(InterruptedException iE){}
67  } 
68
69  public synchronized void endWrite() {
70    nWriters--;
71    if(nWriters>0)
72      writerMutex.mutNotify();
73    else
74      readerMutex.mutNotifyAll();
75  }
76
77}