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ReentrantReadWriteLockUpAndDown.java
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ReentrantReadWriteLockUpAndDown.java
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package git.snippets.juc;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* 读锁无法升级为写锁
* 写锁可以降级成读锁
*
* @author <a href="mailto:410486047@qq.com">Grey</a>
* @date 2021/4/21
* @since
*/
public class ReentrantReadWriteLockUpAndDown {
private static final ReentrantReadWriteLock reentrantLock = new ReentrantReadWriteLock();
private static final ReentrantReadWriteLock.ReadLock readLock = reentrantLock.readLock();
private static final ReentrantReadWriteLock.WriteLock writeLock = reentrantLock.writeLock();
public static void read() {
System.out.println(Thread.currentThread().getName() + "开始尝试获取读锁");
readLock.lock();
try {
System.out.println(Thread.currentThread().getName() + "获取读锁,开始执行");
Thread.sleep(20);
System.out.println(Thread.currentThread().getName() + "尝试升级读锁为写锁");
//读锁升级为写锁(失败)
writeLock.lock();
System.out.println(Thread.currentThread().getName() + "读锁升级为写锁成功");
} catch (Exception e) {
e.printStackTrace();
} finally {
readLock.unlock();
System.out.println(Thread.currentThread().getName() + "释放读锁");
}
}
public static void write() {
System.out.println(Thread.currentThread().getName() + "开始尝试获取写锁");
writeLock.lock();
try {
System.out.println(Thread.currentThread().getName() + "获取写锁,开始执行");
Thread.sleep(40);
System.out.println(Thread.currentThread().getName() + "尝试降级写锁为读锁");
//写锁降级为读锁(成功)
readLock.lock();
System.out.println(Thread.currentThread().getName() + "写锁降级为读锁成功");
System.out.println();
} catch (Exception e) {
e.printStackTrace();
} finally {
System.out.println(Thread.currentThread().getName() + "释放写锁");
writeLock.unlock();
readLock.unlock();
}
}
public static void main(String[] args) {
new Thread(ReentrantReadWriteLockUpAndDown::write, "Thread1").start();
new Thread(ReentrantReadWriteLockUpAndDown::read, "Thread2").start();
}
}