CODEWITHSUNDEEP
javamultithreadingjava.util.concurrentlocksstampedlock
my name is GYAN
my name is GYAN

Reputation: 1289

How exactly does the tryOptimisticRead() method of the StampedLock class work?

I am working on the following codes.

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);      
     }
}

Output:

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)

It seems that both threads never got read lock. How does this method work?

Upvotes: 0

Views: 599

Answers (1)

Thomas Krieger
Thomas Krieger

Reputation: 1643

tryOptimisticRead indeed does no locking. Use the method readLock for that. You can use tryOptimisticRead to check if some other thread changed something inside the lock using validate. You do not need to unlock something since you did not lock anything

Upvotes: 1

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