What is the correct way to stop a thread waiting for network activity?

Question

This question has no doubt been asked in various forms in the past, but not so much for a specific scenario.

What is the most correct way to stop a Thread that is blocking while waiting to receive a network message over UDP.

For example, say I have the following Thread:

public class ClientDiscoveryEngine extends Thread {

    private final int PORT;

    public ClientDiscoveryEngine(final int portNumber) {
        PORT = portNumber;
    }

    @Override
    public void run() {
        try {
            socket = new DatagramSocket(RECEIVE_PORT);

            while (true) {
                final byte[] data = new byte[256];
                final DatagramPacket packet = new DatagramPacket(data, data.length);

                socket.receive(packet);
            }
        } catch (SocketException e) {
            // do stuff 1
        } catch (IOException e) {
            // do stuff 2
        }
    }
}

Now, would the more correct way be using the interrupt() method? For example adding the following method:

@Override
public void interrupt() {
    super.interrupt();
    // flip some state?
}

My only concern is, is socket.receive() not a non-interruptable blocking method? The one way that I have thought of would be to implement the interrupt method as above, in that method call socket.close() and then cater for it in the run method in the catch for the SocketException. Or maybe instead of while(true) use some state that gets flipped in the interrupt method. Is this the best way? Or is there a more elegant way?

Thanks

score 4 · Accepted Answer · answered Aug 20 '11 at 14:26

The receive method doesn't seem to be interruptible. You could close the socket: the javadoc says:

Any thread currently blocked in receive(java.net.DatagramPacket) upon this socket will throw a SocketException

You could also use setSoTimeout to make the receive method block only for a small amount of time. After the method has returned, your thread can check if it has been interrupted, and retry to receive again for this small amount of time.

score 3 · Answer 2 · edited May 23 '17 at 10:29

3

Read this answer Interrupting a thread that waits on a blocking action?

edited May 23 '17 at 10:29

Community

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answered Aug 20 '11 at 14:18

aalku

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score 2 · Answer 3 · answered Aug 20 '11 at 14:25

To stop a thread, you should not user neither interrupt nor stop in java. The best way, as you suggested by the end of your question, is to have the loop inside the main method controlled by a flag that you can rise as needed.

Here is an old link about this : http://download.oracle.com/javase/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html

Other ways of stopping a thread are deprecated and don't provide as much control as this one. Also, this may have changed a bit with executor services, I didn't have time to learn much about it yet.

Also, if you want to avoid your thread to be blocked in some IO state, waiting for a socket, you should give your socket a connection and reading time out (method setSoTimeout).

Regards, Stéphane

Err, no. interrupt is there to stop a thread. It's actually the only way to do it if the thread might be blocked in a blocking call which reacts to interrupts (like Thread.sleep, Object.wait, reading from an interruptible channel, etc.). Read http://download.oracle.com/javase/tutorial/essential/concurrency/interrupt.html. — JB Nizet, Aug 20 '11 at 14:32

score 0 · Answer 4 · answered Aug 21 '11 at 00:52

0

This is one of the easier ones. If it's blocked on a UDP socket, send the socket a UDP message that instructs the receiving thread to 'stop'.

Rgds, Martin

answered Aug 21 '11 at 00:52

Martin James

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What is the correct way to stop a thread waiting for network activity?

4 Answers4