java.util.concurrent.locks.ReadWriteLock接口允许一次读取多个线程,但一次只能写入一个线程.
Read Lock : 如果没有线程锁定ReadWriteLock进行写入,则多个线程可以访问读锁定.
写锁定 : 如果没有线程在读或写,那么一个线程就可以访问写锁.
以下是Lock类中可用的重要方法列表.
Sr.No. | 方法&说明 |
---|---|
1 | public Lock readLock() 返回用于读取的锁. |
2 | public Lock writeLock() 返回用于写入的锁. |
以下TestThread程序演示了ReadWriteLock接口的这些方法.这里我们使用readlock()获取read-lock和writeLock()来获取写锁.
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.
Writer A Time Taken 6 seconds. Write Lock Present. Writer B Time Taken 2 seconds. Reader Time Taken 0 seconds. Reader: aab