Can I invoke XMPPConnection.sendPacket from concurrent threads?

Question

Motivation

I want extra eyes to confirm that I am able to call this method XMPPConnection.sendPacket( Packet ) concurrently. For my current code, I am invoking a List of Callables (max 3) in a serial fashion. Each Callable sends/receives XMPP packets on the one piece of XMPPConnection. I plan to parallelize these Callables by spinning off multiple threads & each Callable will invoke sendPacket on the shared XMPPConnection without synchronization.

XMPPConnection

class XMPPConnection
{
    private boolean connected = false;

    public boolean isConnected() 
    {
        return connected;
    }

    PacketWriter packetWriter;

    public void sendPacket( Packet packet ) 
    {
        if (!isConnected())
            throw new IllegalStateException("Not connected to server.");

        if (packet == null) 
            throw new NullPointerException("Packet is null.");

        packetWriter.sendPacket(packet);
    }
}

PacketWriter

class PacketWriter
{
    public void sendPacket(Packet packet) 
    {
        if (!done) {
            // Invoke interceptors for the new packet 
            // that is about to be sent. Interceptors
            // may modify the content of the packet.
            processInterceptors(packet);

            try {
                queue.put(packet);
            }
            catch (InterruptedException ie) {
                ie.printStackTrace();
                return;
            }
            synchronized (queue) {
                queue.notifyAll();
            }

            // Process packet writer listeners. Note that we're 
            // using the sending thread so it's expected that 
            // listeners are fast.
            processListeners(packet);
    }

    protected PacketWriter( XMPPConnection connection ) 
    {
        this.queue = new ArrayBlockingQueue<Packet>(500, true);
        this.connection = connection;
        init();
    }
}

What I conclude

Since the PacketWriter is using a BlockingQueue, there is no problem with my intention to invoke sendPacket from multiple threads. Am I correct ?

Answer 1

Yes you can send packets from different threads without any problems.

The Smack blocking queue is because what you can't do is let the different threads write the output stream at the same time. Smack takes the responsibility of synchronizing the output stream by writing it with a per packet granularity.

The pattern implemented by Smack is simply a typical producer/consumer concurrency pattern. You may have several producers (your threads) and only one consumer (the Smack's PacketWriter running in it's own thread).

Regards.