10000 concurrent connection using Java NIO

Question

I wrote a Server(similar to one here) and Client code using Java nio.

I am trying to achieve as many connections as possible. From previous suggestions I slowed down

Answer 1

socketChannel.register(selector, SelectionKey.OP_WRITE|SelectionKey.OP_READ);

This is incorrect usage. Your selector will spin, as OP_WRITE is almost always ready, except at the rare times when the socket send buffer is full. This is why you're not processing OP_ACCEPT as fast as you could. You're busy processing OP_WRITE at times when you have nothing to write.

The correct way to use OP_WRITE is as follows:

• Register a newly accepted channel for OP_READ only
• When you have something to write to the channel, just write it
• If that write returns zero, register the channel for OP_WRITE, save the ByteBuffer you were trying to write, and return to the select loop
• When OP_WRITE fires on the channel, call write() with the same buffer
• if that write succeeds and doesn't return zero, register OP_READ again, or at least remove OP_WRITE from the interestOps.

NB Closing a channel cancels its key. You don't need the cancel.