java.util.concurrent.locks.ReadWriteLock是JDK5提供的读写分离锁;
- 读-读不互斥:读读之间不阻塞;
- 读-写互斥:读阻塞写,写阻塞读;
- 写-写互斥:写写阻塞;
在系统中,如果读操作次数远远大于写操作次数,则读写锁可以发挥最大的功效,提升系统的性能;
public class ReadWriteLockDemo {
private static Lock lock = new ReentrantLock();
private static ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
private static Lock readLock = readWriteLock.readLock();
private static Lock writeLock = readWriteLock.writeLock();
private int value;
public Object handleRead(Lock lock) throws InterruptedException {
try {
// 模拟读操作
lock.lock();
// 读操作耗时越多,读写锁优势越明显
TimeUnit.SECONDS.sleep(1);
return value;
} finally {
lock.unlock();
}
}
public void handleWrite(Lock lock, int index) throws InterruptedException {
try {
// 模拟写操作
lock.lock();
TimeUnit.SECONDS.sleep(1);
value = index;
} finally {
lock.unlock();
}
}
public static void main(String[] args) {
final ReadWriteLockDemo rwld = new ReadWriteLockDemo();
Runnable readRunnable = new Runnable() {
@Override
public void run() {
try {
rwld.handleRead(readLock);
// rwld.handleRead(lock);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
Runnable writeRunnable = new Runnable() {
@Override
public void run() {
try {
rwld.handleWrite(writeLock, new Random().nextInt());
// rwld.handleWrite(lock, new Random().nextInt());
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
for (int i = 0; i < 10; i++) {
new Thread(readRunnable).start();
}
for (int i = 0; i < 10; i++) {
new Thread(writeRunnable).start();
}
}
}
代码中使用休眠1秒模拟读写操作,如果使用读写锁,读读不阻塞,一共耗时10秒左右;如果使用普通的重入锁,读读也阻塞,一共耗时20秒左右;