參考package EDU.oswego.cs.dl.util.concurrent
1
public interface Sync 
{
2
public void acquire();
3 public void release();
4
}
1/**//**
2 * A simple Sempahore implementaion.
3 *
4 * @author sakis
5 */
6public class Semaphore implements Sync{
7 private int value;
8
9
/**//**
10 * Sempahore(1) is a Mutex.
11
*/
12 public Semaphore() {
13 value = 1;
14 }
15
16 public Semaphore(int value) {
17 this.value = value;
18 }
19
20 /**//**
21 * P(): waits until the semaphore's value is greater than zero( there are
22 * enough resources to use), then decrements it.
23 */
24 synchronized public void acquire() {
25 while (value <= 0) {
26 try {
27 wait();
28 } catch (InterruptedException e) {
29 }
30 }
31 --value;
32 }
33
34 /**//**
35 * V(): increments the semaphore's value(release one resource), and wakes up
36 * threads waiting in P() if possible.
37 */
38 synchronized public void release() {
39 ++value;
40 notify();
41 }
42}
1/**//**
2 * 讀-寫鎖，讀者和寫者互斥，寫者之間互斥。
3 * Standard usage:
4 * class X {
5 * ReadWriteLock rw;
6 * //
7 * public void read() throws InterruptedException {
8 * rw.readLock().acquire();
9 * try {
10 * // do the read
11 * }
12 * finally {
13 * rw.readlock().release()
14 * }
15 * }
16 *
17 * public void write() throws InterruptedException {
18 * rw.writeLock().acquire();
19 * try {
20 * // do the write
21 * }
22 * finally {
23 * rw.writelock().release()
24 * }
25 * }
26 * }
27 * @see NoPreferenceReadWriteLock
28 * NoPreferenceReadWriteLockWithSemaphore
29 * WriterPreferenceReadWriteLock
30 */
31public interface ReadWriteLock {
32 public Sync readLock();
33 public Sync writeLock();
34}
第一種讀寫鎖實現，使用java的管程，reader和writer優先級相同
1/**//**
2 * WriteReadLock implementation, reader writer have same priority.
3 * @author sakis
4 */
5public class NoPreferenceReadWriteLock implements ReadWriteLock {
6 private static int readCount = 0;
7 private static final int FREE = 0;
8 private static final int READING = 1;
9 private static final int WRITING = 2;
10 private int status = FREE;
11 private final ReadLock readLock = new ReadLock();
12 private final WriteLock writeLock = new WriteLock();
13
14 public Sync readLock() {
15 return readLock;
16 }
17
18 public Sync writeLock() {
19 return writeLock;
20 }
21
22 private class ReadLock implements Sync {
23 public void acquire() {
24 beforeRead();
25 }
26
27 public void release() {
28 afterRead();
29 }
30 }
31
32 private class WriteLock implements Sync {
33 public void acquire() {
34 beforeWrite();
35 }
36
37 public void release() {
38 afterWrite();
39 }
40 }
41
42 private synchronized void beforeRead() {
43 while (!canRead()) {
44 try {
45 wait();
46 } catch (InterruptedException e) {
47 }
48 }
49 // If I'm the first reader, mark the status as READING.
50 if (++readCount == 1)
51 setStatus(READING);
52 }
53
54 private synchronized void afterRead() {
55 // If I'm the last reader, mark the status as FREE.
56 // and wake up one writer who waits on the database.
57 if (--readCount == 0) {
58 setStatus(FREE);
59 notify();
60 }
61 }
62
63 private synchronized void beforeWrite() {
64 // Wait until nobody is writing or reading the database.
65 while (!canWrite()) {
66 try {
67 wait();
68 } catch (InterruptedException e) {
69 }
70 }
71 // mark the status as WRITING.
72 setStatus(WRITING);
73 }
74
75 private synchronized void afterWrite() {
76 // After writing, mark the status as FREE.
77 // and wake up all readers who waits on the database.
78 setStatus(FREE);
79 notifyAll();
80 }
81
82 private boolean canRead() {
83 return status == FREE || status == READING;
84 }
85
86 private boolean canWrite() {
87 return status == FREE;
88 }
89
90 private void setStatus(int status) {
91 this.status = status;
92 }
93
94}
第二種讀寫鎖實現，使用信號量，reader和writer優先級相同
1/**//**
2 * WriteReadLock implementation using Semaphore,
3 * reader writer have same priority.
4 * @author sakis
5 */
6public class NoPreferenceReadWriteLockWithSemaphore implements ReadWriteLock {
7 private static int readCount = 0;
8 private Semaphore rcMutex = new Semaphore();
9 private Semaphore dataMutex = new Semaphore();;
10 private final ReadLock readLock = new ReadLock();
11 private final WriteLock writeLock = new WriteLock();
12
13 public Sync readLock() {
14 return readLock;
15 }
16
17 public Sync writeLock() {
18 return writeLock;
19 }
20
21 private class ReadLock implements Sync {
22 public void acquire() {
23 beforeRead();
24 }
25
26 public void release() {
27 afterRead();
28 }
29 }
30
31 private class WriteLock implements Sync {
32 public void acquire() {
33 beforeWrite();
34 }
35
36 public void release() {
37 afterWrite();
38 }
39 }
40
41 private synchronized void beforeRead() {
42 rcMutex.acquire();
43 // If i'm the first reader, disallow writer
44 // to access the database by dataMutex.P();
45 if (++readCount == 1)
46 dataMutex.acquire();
47 rcMutex.release();
48 }
49
50 private synchronized void afterRead() {
51 rcMutex.acquire();
52 // If I'm the last reader, re-allow writer
53 // to access the database by dataMutex.V();
54 if (--readCount == 0)
55 dataMutex.release();
56 rcMutex.release();
57 }
58
59 private synchronized void beforeWrite() {
60 // disallow other readers,writers to access
61 // the database.
62 dataMutex.acquire();
63 }
64
65 private synchronized void afterWrite() {
66 dataMutex.release();
67 }
68} 第三種讀寫鎖實現，使用信號量，writer優先級高。
@see EDU.oswego.cs.dl.util.concurrent.WriterPreferenceReadWriteLock
1/**//**
2 * WriteReadLock implementation, writer has higher priority.
3 */
4public class WriterPreferenceReadWriteLock implements ReadWriteLock {
5
6 private long waitingReaders = 0; // threads try to read
7 private long waitingWriters = 0; // threads try to write
8
9 private long activeReaders = 0; // threads excuting read
10 private long activeWriters = 0; // threads excuting write, 0 or 1
11
12 private final ReadLock readLock = new ReadLock();
13 private final WriteLock writeLock = new WriteLock();
14
15 /**//*
16 * @see mis0204.tao.concurrent.ReadWriteLock#readLock()
17 */
18 public Sync readLock() {
19 return readLock;
20 }
21
22 /**//*
23 * @see mis0204.tao.concurrent.ReadWriteLock#writeLOck()
24 */
25 public Sync writeLock() {
26 return writeLock;
27 }
28
29 private class ReadLock implements Sync {
30 public void acquire() {
31 beforeRead();
32 }
33
34 public void release() {
35 afterRead();
36 }
37 }
38
39 private class WriteLock implements Sync {
40 public void acquire() {
41 beforeWrite();
42 }
43
44 public void release() {
45 afterWrite();
46 }
47 }
48
49 private synchronized void beforeRead() {
50 ++waitingReaders;
51 while (!canRead()) {
52 try {
53 wait();
54 } catch (InterruptedException e) {
55 --waitingReaders; // roll back state
56 e.printStackTrace();
57 }
58 }
59 --waitingReaders;
60 ++activeReaders;
61 }
62
63 private synchronized void afterRead() {
64 --activeReaders;
65 notifyAll();
66 }
67
68 private synchronized void beforeWrite() {
69 ++waitingWriters;
70 while (!canWrite()) {
71 try {
72 wait();
73 } catch (InterruptedException e) {
74 --waitingWriters; // roll back state
75 e.printStackTrace();
76 }
77 }
78 --waitingWriters;
79 ++activeWriters;
80 }
81
82 private synchronized void afterWrite() {
83 --activeWriters;
84 notifyAll();
85 }
86
87 /**//**
88 * @return true if no writers are waiting/writing on the resource.
89 */
90 private boolean canRead() {
91 return waitingWriters == 0 && activeWriters == 0;
92 }
93
94 /**//**
95 * @return true if no readers/writers are using the resouce.
96 */
97 private boolean canWrite() {
98 return activeReaders == 0 && activeWriters == 0;
99 }
100} end