Java threads trouble (wait() and notify())

smoothdogg00 · #1 07-Apr-2006, 21:29

I have a main program, which starts two separate threads Sender and Receiver. Those threads extend Thread, and they contain the following:

main (Server.java)

JAVA Code:

public void main(){
  receiver = new Receiver();
  receiver.start();

  sender = new Sender();
  sender.start();
}

Receiver

JAVA Code:

public void run(){
  while(true)
  {
    wait();
    DO STUFF
    Server.sender.notify();
  }
}

Sender

JAVA Code:

public void run(){
  while(true)
  {
    Server.receiver.notify();
    wait();
    DO STUFF
  }
}

As you can see, I would like the receiver to do all of its stuff first, then have the sender do all of its stuff, and have them keep trading off in an infinite loop. The error I'm getting is:

JAVA Code:

Exception in thread "Thread-2" java.lang.IllegalMonitorStateException: current thread not owner

Thanks,
Bill

TurboPT · #2 08-Apr-2006, 13:16

Can you possibly share more source of what you're trying to do? It is not clear if "DO STUFF" might be sharing any functionality.

TurboPT · #3 08-Apr-2006, 14:50

I found a reference that says notify() [and notifyAll() for a ThreadGroup] can only be used within synchronized code. That why I am curious about "DO STUFF".

TurboPT · #4 08-Apr-2006, 16:45

Never mind your source. I came up with this for an example:

JAVA Code:

public class ThreadPlay
{
	public static void main(String args[])
	{
		SynchronizedReceiverAndSender s =
			new SynchronizedReceiverAndSender();
		Receiver receiver = new Receiver(s);
		Sender sender = new Sender(s);

		System.out.println("Starting threads...");
		receiver.start();
		sender.start();
		System.out.println("Threads started!");
	}
}

class Receiver extends Thread
{
	private SynchronizedReceiverAndSender receiverRun;

	public Receiver(SynchronizedReceiverAndSender s)
	{
		super("RECEIVER:");
		receiverRun = s;
	}

	public void run()
	{
		while (true)
		{
			try
			{
				Thread.sleep( 2500 );
			}
			catch (InterruptedException ie )
			{}

			receiverRun.processReceiver();
		}
	}
}

class Sender extends Thread
{
	private SynchronizedReceiverAndSender senderRun;

	public Sender(SynchronizedReceiverAndSender s)
	{
		super("SENDER:");
		senderRun = s;
	}

	public void run()
	{
		while (true)
		{
			try
			{
				Thread.sleep( 2500 );
			}
			catch (InterruptedException ie )
			{}

			senderRun.processSender();
		}
	}
}

class SynchronizedReceiverAndSender
{
	// initializing false forces the 'Sender' to wait first.
	// change to true will make the 'Receiver' wait first.
	private boolean myTurn = false;

	public synchronized void processReceiver()
	{
		while (myTurn) // not the Sender's turn.
		{
			try
			{
				wait();
			} catch (InterruptedException ie ) {}
		}

		// your DO stuff here
                System.out.println(Thread.currentThread().getName() +
							" process info...");

		myTurn = true;
		notify();
	}

	public synchronized void processSender()
	{
		while (!myTurn) // not the Receiver's turn.
		{
			try
			{
				wait();
			} catch (InterruptedException ie ) {}
		}

                // your DO STUFF here.
		System.out.println(Thread.currentThread().getName() +
							" send info. to receiver");

		myTurn = false;
		notify();
	}
}

... and here's the console output...

Starting threads...
Threads started!
RECEIVER: process info...
SENDER: send info. to receiver
RECEIVER: process info...
SENDER: send info. to receiver
RECEIVER: process info...
SENDER: send info. to receiver
RECEIVER: process info...
SENDER: send info. to receiver
...

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Java threads trouble (wait() and notify())

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