package lock.readwrite;import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.ReentrantReadWriteLock;/*** 描述： 演示ReentrantReadWriteLock可以降級，不能升級*/ public class Upgrading {private static ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock(false);private static ReentrantReadWriteLock.ReadLock readLock = reentrantReadWriteLock.readLock();private static ReentrantReadWriteLock.WriteLock writeLock = reentrantReadWriteLock.writeLock();private static void readUpgrading() {readLock.lock();try {System.out.println(Thread.currentThread().getName() + "得到了讀鎖，正在讀取");Thread.sleep(1000);System.out.println("升級會帶來阻塞");writeLock.lock();System.out.println(Thread.currentThread().getName() + "獲取到了寫鎖，升級成功");} catch (InterruptedException e) {e.printStackTrace();} finally {System.out.println(Thread.currentThread().getName() + "釋放讀鎖");readLock.unlock();}}private static void writeDowngrading() {writeLock.lock();try {System.out.println(Thread.currentThread().getName() + "得到了寫鎖，正在寫入");Thread.sleep(1000);readLock.lock();System.out.println("在不釋放寫鎖的情況下，直接獲取讀鎖，成功降級");} catch (InterruptedException e) {e.printStackTrace();} finally {readLock.unlock();System.out.println(Thread.currentThread().getName() + "釋放寫鎖");writeLock.unlock();}}public static void main(String[] args) throws InterruptedException { // System.out.println("先演示降級是可以的"); // Thread thread1 = new Thread(() -> writeDowngrading(), "Thread1"); // thread1.start(); // thread1.join(); // System.out.println("------------------"); // System.out.println("演示升級是不行的");Thread thread2 = new Thread(() -> readUpgrading(), "Thread2");thread2.start();} }

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