StampedLock作为JAVA8中出现的新型锁，很可能在大多数场景都可以替代ReentrantReadWriteLock。它对于读/写都提供了四个接口(换成write为写锁)：
- readLock()
- tryReadLock()
- tryReadLock(long time, TimeUnit unit)
- readLockInterruptibly()
这几个方法对应的语义为：
- 获取读锁（阻塞，不响应中断）
- 获取读锁（立即）
- 限时获取读锁（响应中断）
- 获取读锁（阻塞，响应中断）
然而在readLock方法（即不响应中断）中存在问题(write的版本也是)，观察CPU使用率，执行以下代码：
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public class TestStampedLock {
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public static void main(String[] args) throws InterruptedException{
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final StampedLock lock = new StampedLock();
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new Thread(){
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public void run(){
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long readLong = lock.writeLock();
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LockSupport.parkNanos(6100000000L);
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lock.unlockWrite(readLong);
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}
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}.start();
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Thread.sleep(100);
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for( int i = 0; i < 3; ++i)
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new Thread(new OccupiedCPUReadThread(lock)).start();
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}
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private static class OccupiedCPUReadThread implements Runnable{
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private StampedLock lock;
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public OccupiedCPUReadThread(StampedLock lock){
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this.lock = lock;
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}
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public void run(){
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Thread.currentThread().interrupt();
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long lockr = lock.readLock();
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System.out.println(Thread.currentThread().getName() + " get read lock");
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lock.unlockRead(lockr);
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}
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}
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} |
先开启一个线程获取写锁并保持6秒，再开启三个带着中断状态的线程去获取读锁（readLock方法），结果是3个核心被占据了近6秒。
原因在于没有使用保存/复原中断状态的机制，通过hack源码，插入保存中断和返回前恢复中断的相关代码即可修复：
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boolean interrupted = false;
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if(interrupted)
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Thread.currentThread().interrupt();
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return ns;
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if(Thread.interrupted()){
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if(interruptible)
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return cancelWaiter(node, p, true);
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else
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interrupted = true;
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} |
时间： 2024-10-31 19:21:12