NIO and traditional sockets

Question

I have a little server that I was porting from traditional thread per socket programming to NIO. The first thing I ported was the Listen-Accept loop. This worked well but the resulting sockets obtained from
SocketChannel.socket()
have very strange behaviour with respect to flush. I send the data by
out.write(data);
out.flush();
where out is the BufferedOutputStream. The data doesn't get sent until the next input arrives on the Socket. If I change to using just old style I/O or completely NIO the problem goes away.
I found several bug reports on NIO and flush, but they all seem to be considered Feechures by SUN.

Answer 1

Thanks for posting the link to your NIO code. I downloaded the src-raining-1.2pre1 source and took a look. I noticed that you still have some doubts about how OP_WRITE works. This piece of code will definitely have problems.
    public void setSendData(ByteBuffer data) {
        this.write_pending = true;
        wBuffer = data;
        //RK modified on 20031008 23:19:39 - NOOO
                //registerChannel(selector, channel(), SelectionKey.OP_WRITE);
        // RK modified on 20031009 23:15:00 adding write interest
        SelectionKey sk = sc.keyFor(selector);
        int ops = sk.interestOps();
        sk.interestOps( ops | SelectionKey.OP_WRITE);
        selector.wakeup(); // is this required or not ???
    }The sk.interestOps will block if there is an active select. If there isn't an active select you don't need the wakeup. The only way to make this work properly in 1.4.2 is to build a queue of runnables that set interestOps and execute them just before or after the select. Also the setting of OP_WRITE in that code won't handle the case where the network exerts flow control on the channel. The correct setting of OP_WRITE is
- set interest in OP_WRITE when the socket is connected
- remove interest as soon as you successfully write all the data in a buffer
- add interest only when you write less bytes than requested.
My post Taming the NIO Circus provides an example of this in the swing based client. I posted this in response to Java.nio. SelectionKey interestOps(int) method blocks