Not more than 4 Worker threads

[Marc-André Laverdière]

When you are creating your server, how big are you making your worker pool?

Marc-André LAVERDIÈRE
"Perseverance must finish its work so that you may be mature and complete,
not lacking anything." -James 1:4
http://asimplediscipleslife.blogspot.com/
mlaverd.theunixplace.com





On Fri, Jun 10, 2011 at 12:00 AM, Rajkumar S <rajkumars at gmail.com> wrote:
> Hello all,
>
> I am testing out netty for a project of mine and started out with the
> DiscardServer in the user guide. To simulate a processing delay of 3
> seconds and to observe how the system will behave when there is a
> processing delay in messageReceived I added a sleep of 3 seconds to
> messageReceived in DiscardServerHandler  as shown below:
>
>   public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
>        ChannelBuffer buf = (ChannelBuffer) e.getMessage();
>        while(buf.readable()) {
>            System.out.print((char) buf.readByte());
>            System.out.flush();
>        }
>        try {
>                Thread.sleep(3000);
>        } catch(Exception ev){}
>    }
>
>
> The client program is a simple perl program that connects to the
> server and transmit one line of text. This perl program is started 100
> times by a loop in in a shell script to simulate 100 concurrent
> connection.
>
> I was expecting the DiscardServer to launch 100 worker threads where
> each will print all the incoming message in one step and then sleep
> for 3 seconds.
>
> What I observed was that 4 messages are printed, then wait for 3
> seconds, again 4 messages and 3 seconds wait till all the messages are
> printed. During this time can see the connections that are not
> processed in netstat.  They are are in CLOSE_WAIT and Recv-Q  has a
> size of 6 (which is the number of characters in the line of text sent
> by client) During every 3 seconds 4 connections will disappear from
> netstat output as they are processed by DiscardServer. An example line
> from netstart is as follows:
>
> tcp6       6      0 192.168.3.18:8080       192.168.3.18:41671      CLOSE_WAIT
>
> Now my questions are:
>
> 1. Is this the expected behavior?
> 2. Why didn't the number of threads increase to process the
> connections that were available?
> 3. Why the magic number of 4? (I am using a Core2 Duo CPU with 2
> cores) I tried to use newFixedThreadPool but the number of threads
> started does not go above 4, but it does come down if a number < 4 is
> used.
> 4. In a real world application if there is a heavy processing involved
> for received messages (say takes three seconds to process each
> message) is the correct approach to add that to messageReceived
> method?
> 5. Am i missing any thing here? :)
>
> I am just trying to get a hang of the natty library and event driven
> programming in general. So please excuse me asking so many trivial
> questions!
>
> Thanks and regards,
>
> raj
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