StampedLock类的tryOptimisticRead（）方法如何工作？

Question

我正在处理以下代码。

CreateThread.java

import java.util.concurrent.locks.*;
class CreateThread
{   
   public static void main(String[] args)   
   {        
      StampedLock lock = new StampedLock();         
      MyThread[] t = new MyThread[5];       
      for(int i=0; i<2; i++)        
      {         
        t[i] = new MyThread("t"+i, lock);       
      }     
      for(int i=0; i<2; i++)        
      {         
         t[i].start();      
      } 
    }
}

MyThread.java

import java.util.concurrent.locks.*;
public class MyThread extends Thread
{ 
   StampedLock lock = null;    
   public MyThread(String name, StampedLock lock)    
   {    
     super(name);   
     this.lock=lock;    
    }     
    public void run()    
    {       
       long stamp = 0;
       stamp = lock.tryOptimisticRead();        
       System.out.println(Thread.currentThread().getName()+" applied for Lock "+ stamp);
       if(lock.validate(stamp))
       {
        System.out.println(Thread.currentThread().getName()+" got Lock "+ lock);
       }
       try      
       {            
         Thread.sleep(5000);        
       }        
       catch(InterruptedException e){}      
       lock.unlock(stamp);      
     }
}

输出：

t1 applied for Lock 256
t0 applied for Lock 256
t0 got Lock java.util.concurrent.locks.StampedLock@1ce4c0a1[Unlocked]
t1 got Lock java.util.concurrent.locks.StampedLock@1ce4c0a1[Unlocked]
Exception in thread "t0" java.lang.IllegalMonitorStateException
    at java.base/java.util.concurrent.locks.StampedLock.unlockRead(StampedLock.java:722)
    at java.base/java.util.concurrent.locks.StampedLock.unlock(StampedLock.java:738)
    at MyThread.run(MyThread.java:24)
Exception in thread "t1" java.lang.IllegalMonitorStateException
    at java.base/java.util.concurrent.locks.StampedLock.unlockRead(StampedLock.java:722)
    at java.base/java.util.concurrent.locks.StampedLock.unlock(StampedLock.java:738)
    at MyThread.run(MyThread.java:24)

似乎两个线程都没有读取锁定。这种方法如何工作？

Answer 1

tryOptimisticRead实际上没有锁定。为此，使用方法readLock。您可以使用tryOptimisticRead来使用validate检查其他某个线程是否更改了锁内的某些内容。您没有解锁任何东西，因为您没有锁定任何东西