90% CPU -problem with thread in NIO

[Dave Jones]

Hi Guys,

I have a multi-threaded server written in non blocking NIO (one thread
handles the IO) and after a while i see that it uses
about 90% CPU. I managed to find the thread that causes the problem, and
it is the one handling the IO but i need help understanding the
reason for it, please take a look:
Thanks

// Code segment for connecting channel (handleConnect)
 
       if (connectingChannel.isConnectionPending())
        {
            boolean successfullConnect = false;
            try
            {
                successfullConnect = connectingChannel.finishConnect();
                if (successfullConnect)
                {
                           connectingChannel.write("message"));
                }
            }
            catch (ConnectException connectException)
            {
                // couldn't connect
            }
        }
 
 

I noticed that the problem only started after I got a null pointer
exception in the line: connectingChannel.write...
The thread has a while(true) loop surrounding a try...catch... that
catches this exception and continues normally.

// Code segment for select
 
        int numberOfReadyChannels = ioHandlerSelector.select(1000);
 
        if (numberOfReadyChannels == 0)
        {
            log.finer("No ready channels");
            return;
        }
 
        for (Iterator iter = ioHandlerSelector.selectedKeys().iterator(); iter.hasNext() :wink: 
        {
            log.finest("in iterator loop");
            SelectionKey key = (SelectionKey) iter.next();
            iter.remove();
 
            if (key.isConnectable())
            {
                log.finer("Connectable");
                try
                {
                    handleConnect(key);     //The previous segment
                }
                catch(IOException e1)
                {
                    log.log(Level.WARNING, "Error trying to handleConnect", e1);
                }             
            }
            else if (key.isReadable())
            {
                log.finer("Readable");
                SocketChannel currentSocketChannel = (SocketChannel) key.channel();
                synchronized (currentSocketChannel)
                {
                    try
                    {      
                        handleRead(key);
                    }
                    catch (IOException e)
                    {
                        log.log(Level.WARNING, "Error - Socket reset", e);
                    }
                }
            }
        }
 
 

The reason for the 90% CPU is that ioHandlerSelector.select(1000)
returns immediately (after the exception), and it's surrounded by a
while(true) loop (Every 1-3 ms i see a "no ready channels" msg)


What can be the problem?
Thanks again

[David Harkness]

Don't you have to wait until the channel becomes writable (after connecting) to be able to write to it?