1 package gov.bnl.gums;
2
3 import org.apache.log4j.Logger;
4
5 public class RWLock
6 {
7 private int givenLocks;
8 private int waitingWriters;
9 private Logger log = Logger.getLogger(RWLock.class);
10
11 private Object mutex;
12
13 public RWLock()
14 {
15 mutex = new Object();
16 givenLocks = 0;
17 waitingWriters = 0;
18 }
19
20 public void getReadLock()
21 {
22 synchronized(mutex)
23 {
24 while((givenLocks == -1) || (waitingWriters != 0))
25 try {
26 mutex.wait();
27 } catch (InterruptedException e) {
28 log.error(e);
29 }
30
31 givenLocks++;
32 }
33 }
34
35 public void getWriteLock()
36 {
37 synchronized(mutex)
38 {
39 waitingWriters++;
40 while(givenLocks != 0) {
41 try {
42 mutex.wait();
43 } catch (InterruptedException e) {
44 log.error(e);
45 }
46 }
47
48 waitingWriters--;
49 givenLocks = -1;
50 }
51 }
52
53
54 public void releaseLock()
55 {
56 synchronized(mutex)
57 {
58 if(givenLocks == 0)
59 return;
60
61 if(givenLocks == -1)
62 givenLocks = 0;
63 else
64 givenLocks--;
65
66 mutex.notifyAll();
67 }
68 }
69
70
71 }
72
73
74