The document discusses synchronization and concurrency in Java. It covers synchronized blocks and methods, volatile variables, Lock objects from java.util.concurrent package, and concepts like the Java memory model. It provides examples of using synchronized, volatile and Lock to synchronize access to shared resources in multithreaded programs.

1. Java
Thread
2011 4 9
twitter: @zaki50

2. Who am I
• YAMAZAKI Makoto(twitter: @zaki50)
• Android
•
• StickyShortcut
• Java

3. • Effective Java 2
• ISBN:978-4-89471-499-1
• 3,780 ( )
• 66, 69

4. Agenda
• synchronized / volatile
• Lock(ReentrantLock)
• java.util.concurrent

5. synchronized

6. Eclipse (jvisualvm)

7. synchronized
class Sample {
public synchronized void execute1() {
//
}
public void execute1b() {
synchronized (this) {
//
}
}
public static synchronized void execute2() {
//
}
public static synchronized void execute2b() {
synchronized (Sample.class) {
//
}
}
}

8. synchronized
•
•
•

9. •

11. •
(by Wikipedia)
• Java 1
1
1
1

12. •
• synchronized
• Object#wait()
•
• synchronized
• Object#wait()

13. •
synchronized
•

14. synchronized
class Sample {
public synchronized void execute1() {
//
}
public void execute1b() {
synchronized (this) {
//
}
}
public static synchronized void execute2() {
//
}
public static synchronized void execute2b() {
synchronized (Sample.class) {
//
}
}
}

15. •

16. •

17. • Java VM
•
•
•

18. private static boolean stopRequested = false;
private static int value = 0;
public static void main(String[] args) throws Exception {
new Thread() {
@Override
public void run() {
int i = 0;
if (!stopRequested) {
while (!stopRequested) { while (true) {
i++; i++;
}
}
}
System.out.println(value);
}
}.start();
TimeUnit.SECONDS.sleep(1L);
value = 100;
stopRequested = true;
}

19. private static boolean stopRequested = false;
private static int value = 0;
public static void main(String[] args) throws Exception {
new Thread() {
@Override
public void run() {
int i = 0;
while (!stopped()) {
i++;
}
System.out.println(value);
}
}.start(); private synchronized static void stop() {
stopRequested = true;
TimeUnit.SECONDS.sleep(1L); }
value = 100;
stop(); private synchronized static boolean stopped() {
} return stopRequested;
}

20. volatile

21. volatile
•
• volatile
• volatile

22. volatile
private volatile static boolean stopRequested = false;
private volatile static int value = 0;
public static void main(String[] args) throws Exception {
new Thread() {
@Override
public void run() {
int i = 0;
while (!stopRequested) {
i++;
}
System.out.println(value);
}
}.start();
TimeUnit.SECONDS.sleep(1L);
value = 100;
stopRequested = true;
}

23. Lock

24. Lock
• synchronized
• lock() // synchronized
• tryLock() //
• tryLock(long,TimeUnit) //
• lockInterruptibly() //

25. •
• try - finally
Lock l = ...;
l.lock();
try {
//
} finally {
l.unlock();
}

26. ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
Lock wl = rwLock.writeLock();
Lock rl;
wl.lock();
try {
// write
rl = rwLock.readLock();
} finally {
wl.unlock();
}
try {
// read
} finally {
rl.unlock();
}

27. Lock
• lock() synchronized
• unlock() synchronized
• Lock

28. java.util.concurrent

29. ...
• wait() notify()/notifyAll()
( )
•

30. java.util.concurrent
•
Javadoc of java.util.concurrent
• ExecutorService
•
•
•
• ConcurrentCollections
•

31. • synchronized
• Java 17.4 Memory Model
• java.util.concurrent
• Java
• Doug Lea ISBN:4-7973-3720-6