Question on Threads?

[Anuradha Prasanna]

Hi,

In the following program,

package Thread;
public class SyncThread implements Runnable{
	
private static SyncThread sync;
private String name;

	public void run(){
		synchronized(sync){  // line 1
		for(int i=0;i<400;i++){
			System.out.println("i = "+i);
		setName("anu");
		}
		System.out.println("Bye from "+Thread.currentThread().getName());
		}
	}

	public  void  setName(String name){	
		System.out.println("Run by " +Thread.currentThread().getName());
		this.name = name;		
	}
	
	public static void main(String[] args) {
		 sync = new SyncThread();	
		Thread t1 = new Thread(sync);
		t1.setName("Lucy");
		t1.start();
		
		SyncThread sync1 = new SyncThread();
		Thread t2 = new Thread(sync1);
		t2.setName("Sam");
		t2.start();
	}
}

The synchronized lock on line 1, does not let threads Lucy and Sam into the blocked code at the same time?
ie)if Lucy enters the synchronized block on line 1 and acquires the lock of "sync" , then Sam cannot enter the synchronized block on line 1 untill Lucy releases the lock?

Is that right?

[Larry Chung]

Yes, either Lucy or Sam can enter the synchronized block but not at the same time.

It is not guaranteed who will be the first to enter.

[Innar Made]

Hey Anuradha,

Yes, you are correct.

No other thread can't get into the synchronized block while some thread owns the sync object's lock. When the synchronized block finishes then sync object lock is released and other threads can start to compete to get it. Whoever gets it can then enter the synchronized block.