Thread Doubt

[Abhi vijay]

Can anyone expalin me the flow of this program??? What exactly happens when synchronized(b) is called? and what is synchronised(this)?
Thanks, in advance.

public class ThreadA
{
public static void main(String[] args)
{
ThreadB b=new ThreadB();
b.start();
 
synchronized(b)
{
try
{
b.wait();
}
catch(InterruptedException e)
{
}
}
 
System.out.println(" Total " + b.total);
 
}
}
 
          class ThreadB extends Thread
{
int total;
public void run()
{
System.out.println("ThreadB waiting for wait()");
synchronized(this)
{for(int i=1;i<=100;i++)
total= total+i;
notify();
}
System.out.println(" Total " + total);
}
}

[ October 16, 2008: Message edited by: Abhi vijay ]

[edit]Add code tags. CR[/edit]
[ October 17, 2008: Message edited by: Campbell Ritchie ]

[Campbell Ritchie]

Please find the code button because it preserves the indentation.

Please tell us what you think the flow through the program is; you should by now know that we expect people to have tried things themselves already.

[Abhi vijay]

synchronized(b)

This line implies that the thread executing the synchronized block has a lock on the object b...??

try {
b.wait();
}

when wait() is invoked the thread gives up the lock on the object.

But I dont understand when synchronized(this) is called, it is referring to which object and which thread is executing it???

[Campbell Ritchie]

You might get more answers if I move this thread to the threads forum.

[Steve Luke]

Originally posted by Abhi vijay:
synchronized(b)

This line implies that the thread executing the synchronized block has a lock on the object b...??

try {
b.wait();
}

when wait() is invoked the thread gives up the lock on the object.

But I dont understand when synchronized(this) is called, it is referring to which object and which thread is executing it???

The 'this' reference is an object's self reference. So when the class does synchronized(this) it is getting the lock on itself. Which thread is executing it? Any thread that calls the run() method. From your understanding of Threads, when does the run() method get called for a Thread? The API for Thread may help.

[Chris Hurst]

... and don't get into the habit of putting a wait outside a loop ...

http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Object.html#wait()

... in theory that code could give you odd behaviour .