Java Concurrency 简明教程
Java Concurrency - ReadWriteLock Interface
一个 java.util.concurrent.locks.ReadWriteLock 接口允许多个线程一次读取，但一次只能有一个线程写入。
-
Read Lock − 如果没有线程对 ReadWriteLock 进行写锁定，则多个线程可以访问读锁定。
-
Write Lock − 如果没有线程正在读或写，则一个线程可以访问写锁定。
Lock Methods
以下是 Lock 类中可用的重要方法列表。
Sr.No. |
Method & Description |
1 |
public Lock readLock() 返回用于读取的锁。 |
2 |
public Lock writeLock() 返回用于写入的锁。 |
Example
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class TestThread {
private static final ReentrantReadWriteLock lock = new ReentrantReadWriteLock(true);
private static String message = "a";
public static void main(String[] args) throws InterruptedException {
Thread t1 = new Thread(new WriterA());
t1.setName("Writer A");
Thread t2 = new Thread(new WriterB());
t2.setName("Writer B");
Thread t3 = new Thread(new Reader());
t3.setName("Reader");
t1.start();
t2.start();
t3.start();
t1.join();
t2.join();
t3.join();
}
static class Reader implements Runnable {
public void run() {
if(lock.isWriteLocked()) {
System.out.println("Write Lock Present.");
}
lock.readLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
System.out.println(Thread.currentThread().getName() +": "+ message );
lock.readLock().unlock();
}
}
}
static class WriterA implements Runnable {
public void run() {
lock.writeLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
message = message.concat("a");
lock.writeLock().unlock();
}
}
}
static class WriterB implements Runnable {
public void run() {
lock.writeLock().lock();
try {
Long duration = (long) (Math.random() * 10000);
System.out.println(Thread.currentThread().getName()
+ " Time Taken " + (duration / 1000) + " seconds.");
Thread.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
message = message.concat("b");
lock.writeLock().unlock();
}
}
}
}这将产生以下结果。