Examples of java.nio.channels.DatagramChannel

java.nio.channels.DatagramChannel
A DatagramChannel is a selectable channel for part abstraction of datagram socket. The socket method of this class can return the related DatagramSocket instance, which can handle the socket.
A datagram channel is open but not connected when created by open method. After connected, it will keep the connected status before disconnecting or closing. The benefit of a connected channel is the reduced effort of security checks during send and receive. When invoking read or write, a connected channel is required.

Datagram channels are thread-safe, no more than one thread can read or write at given time.

        {
            throw new IllegalArgumentException( "Unexpected local address type: "
                                                + localAddress.getClass() );
        }
        
        DatagramChannel ch = DatagramChannel.open();
        boolean initialized = false;
        try
        {
            ch.socket().setReuseAddress( true );
            if( localAddress != null )
            {
                ch.socket().bind( localAddress );
            }
            ch.connect( address );
            ch.configureBlocking( false );
            initialized = true;
        }
        finally
        {
            if( !initialized )
            {
                ch.disconnect();
                ch.close();
            }
        }


        RegistrationRequest request = new RegistrationRequest( ch, handler );
        synchronized( this )

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        }
    }


    private void flush( DatagramSession session ) throws IOException
    {
        DatagramChannel ch = session.getChannel();


        Queue writeBufferQueue = session.getWriteBufferQueue();
        Queue writeMarkerQueue = session.getWriteMarkerQueue();


        ByteBuffer buf;
        Object marker;
        for( ;; )
        {
            synchronized( writeBufferQueue )
            {
                buf = ( ByteBuffer ) writeBufferQueue.first();
                marker = writeMarkerQueue.first();
            }


            if( buf == null )
                break;


            if( buf.remaining() == 0 )
            {
                // pop and fire event
                synchronized( writeBufferQueue )
                {
                    writeBufferQueue.pop();
                    writeMarkerQueue.pop();
                }


                try
                {
                    buf.release();
                }
                catch( IllegalStateException e )
                {
                    session.getManagerFilterChain().exceptionCaught( session, e );
                }


                session.increaseWrittenWriteRequests();
                session.getManagerFilterChain().dataWritten( session, marker );
                continue;
            }


            SelectionKey key = session.getSelectionKey();
            if( key == null )
            {
                scheduleFlush( session );
                break;
            }
            if( !key.isValid() )
            {
                continue;
            }


            int writtenBytes = ch.write( buf.buf() );


            if( writtenBytes == 0 )
            {
                // Kernel buffer is full
                key.interestOps( key.interestOps() | SelectionKey.OP_WRITE );

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            if( session == null )
                break;
            else
            {
                SelectionKey key = session.getSelectionKey();
                DatagramChannel ch = ( DatagramChannel ) key.channel();
                try
                {
                    ch.disconnect();
                    ch.close();
                }
                catch( IOException e )
                {
                    exceptionMonitor.exceptionCaught( this, e );
                }

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        {
            throw new NullPointerException( "localAddress" );
        }
        
        Selector selector = this.selector;
        DatagramChannel ch = ( DatagramChannel ) channels.get( localAddress );
        if( selector == null || ch == null )
        {
            throw new IllegalArgumentException( "Unknown localAddress: " + localAddress );
        }
            
        SelectionKey key = ch.keyFor( selector );
        if( key == null )
        {
            throw new IllegalArgumentException( "Unknown lodalAddress: " + localAddress );
        }

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        while( it.hasNext() )
        {
            SelectionKey key = ( SelectionKey ) it.next();
            it.remove();


            DatagramChannel ch = ( DatagramChannel ) key.channel();


            RegistrationRequest req = ( RegistrationRequest ) key.attachment();
            DatagramSession session = new DatagramSession(
                    filters, ch, req.handler );
            session.setSelectionKey( key );

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        }
    }


    private void flush( DatagramSession session ) throws IOException
    {
        DatagramChannel ch = session.getChannel();


        Queue writeBufferQueue = session.getWriteBufferQueue();
        Queue writeMarkerQueue = session.getWriteMarkerQueue();


        ByteBuffer buf;
        Object marker;
        for( ;; )
        {
            synchronized( writeBufferQueue )
            {
                buf = ( ByteBuffer ) writeBufferQueue.first();
                marker = writeMarkerQueue.first();
            }


            if( buf == null )
                break;


            if( buf.remaining() == 0 )
            {
                // pop and fire event
                synchronized( writeBufferQueue )
                {
                    writeBufferQueue.pop();
                    writeMarkerQueue.pop();
                }


                try
                {
                    buf.release();
                }
                catch( IllegalStateException e )
                {
                    session.getManagerFilterChain().exceptionCaught( session, e );
                }


                session.increaseWrittenWriteRequests();
                session.getManagerFilterChain().dataWritten( session, marker );
                continue;
            }


            SelectionKey key = session.getSelectionKey();
            if( key == null )
            {
                scheduleFlush( session );
                break;
            }
            if( !key.isValid() )
            {
                continue;
            }


            int writtenBytes = ch
                    .send( buf.buf(), session.getRemoteAddress() );


            if( writtenBytes == 0 )
            {
                // Kernel buffer is full

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            }


            if( req == null )
                break;


            DatagramChannel ch = null;
            try
            {
                ch = DatagramChannel.open();
                ch.configureBlocking( false );
                ch.socket().bind( req.address );
                ch.register( selector, SelectionKey.OP_READ, req );
                channels.put( req.address, ch );
            }
            catch( Throwable t )
            {
                req.exception = t;
            }
            finally
            {
                synchronized( req )
                {
                    req.done = true;
                    req.notify();
                }


                if( ch != null && req.exception != null )
                {
                    try
                    {
                        ch.disconnect();
                        ch.close();
                    }
                    catch( Throwable e )
                    {
                        exceptionMonitor.exceptionCaught( this, e );
                    }

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            if( request == null )
            {
                break;
            }


            DatagramChannel ch = ( DatagramChannel ) channels.remove( request.address );
            // close the channel
            try
            {
                if( ch == null )
                {
                    request.exception = new IllegalArgumentException(
                            "Address not bound: " + request.address );
                }
                else
                {
                    SelectionKey key = ch.keyFor( selector );
                    key.cancel();
                    selector.wakeup(); // wake up again to trigger thread death
                    ch.disconnect();
                    ch.close();
                }
            }
            catch( Throwable t )
            {
                exceptionMonitor.exceptionCaught( this, t );

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        fireChannelOpen(this);
    }


    private DatagramChannel openNonBlockingChannel() {
        try {
            final DatagramChannel channel = DatagramChannel.open();
            channel.configureBlocking(false);
            return channel;
        } catch (final IOException e) {
            throw new ChannelException("Failed to open a DatagramChannel.", e);
        }
    }

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    private boolean read(final SelectionKey key) {
        final NioDatagramChannel channel = (NioDatagramChannel) key.attachment();
        ReceiveBufferSizePredictor predictor =
            channel.getConfig().getReceiveBufferSizePredictor();
        final ChannelBufferFactory bufferFactory = channel.getConfig().getBufferFactory();
        final DatagramChannel nioChannel = (DatagramChannel) key.channel();


        // Allocating a non-direct buffer with a max udp packge size.
        // Would using a direct buffer be more efficient or would this negatively
        // effect performance, as direct buffer allocation has a higher upfront cost
        // where as a ByteBuffer is heap allocated.
        final ByteBuffer byteBuffer = ByteBuffer.allocate(
                predictor.nextReceiveBufferSize()).order(bufferFactory.getDefaultOrder());


        boolean failure = true;
        SocketAddress remoteAddress = null;
        try {
            // Receive from the channel in a non blocking mode. We have already been notified that
            // the channel is ready to receive.
            remoteAddress = nioChannel.receive(byteBuffer);
            failure = false;
        } catch (ClosedChannelException e) {
            // Can happen, and does not need a user attention.
        } catch (Throwable t) {
            fireExceptionCaught(channel, t);

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Datagrams

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