Tuesday, December 1, 2015

Computer users, relax your tired eyes using 20-20-20 rule

We all know that using a computer for a longer time each day, makes your eyes tired. This is a simple rule which may help reduce your eyestrain and let your eyes relax for a while. It is recommended to stand up and stretch once in a while without sitting on your chair all the time. But sometimes it may not be possible to walk in every 30 minutes from your chair. But at least try following 20-20-20 rule to relax your eyes :)

20-20-20 rule:

And try to blink your eyes more so that it will help your eyes to avoid getting dry. 

Wednesday, November 4, 2015

Presentation tips and 10-20-30 Rule for Presentations

When it is required to do a presentation either it is business related or academic, we always want to make it attractive and smart. Following are some of the well known methods that I have been using.

  • Use less text
We know that the audience will get board when you have a lot of text in your slides. If they do not get board, they will start reading the slides without listening to your talk. So you miss the change to emphasis what you want. Either way you loose :(
So if you feel that should have text for a particular slide to explain it easier, try point format and be precise. 3, 4 bullet points with up to 6, 7 words per each bullet will be ideal.

  • Communicate your idea with pictures
We know that "A picture is worth a thousand words". It is always easy and clear to convey your idea through a picture than having a lot of text. (This is a very well known fact)

  • Use simple animations
If some complex concept or an algorithm should be presented, make some animated slides which can explain it easily than trying to struggle with all Xs and Ys. You may feel that it will be clear, but believe me it will not. Just try to memorize the very first time you got to know about that concept. Even though you have mastered it now, for the audience it may be the first time :)

And of course you should not have these complex explanations in your presentation if you do not think that you MUST have them.

  • Less slides and good formatting
Have some attractive formatting, so your audience will not get board seeing it. But of course I did not mean 'fancy' :)

  • 10-20-30 Rule
This was a concept introduced by Guy Kawasaki who is a Silicon Valley marketing executive.
In brief it says
               10 slides only
               20 minutes presentation time
               30 font size
Here is his explanation on how it will be effective. 

And I have some final tip for the audience. If your colleague is doing a presentation for academic purposes and you are supposed to give feedback, please provide the real feedback you have. Do not say that it was amazing just because you think that your friend will feel bad if you didn't do so. I specifically mentioned academic because I believe when it comes to business, it is most probable to have the real feedback since it is business. :)

I personally had this practice of being nice and trying to avoid giving bad feedback and suddenly I realized that I am taking away the change of my colleague to further improve his/her presentation skills. This can be something simple like 'You spoke too fast' but if he improve that, it will help a lot to attract more audience next time. You can of course be polite and convey it nicely, so that it will really help the presenter to improve himself/herself. And may be you can give written feedback too.

So good luck with your next presentation :)

Wednesday, October 7, 2015

Singleton Pattern

This is one of the simplest, yet very useful design pattern. Singleton design pattern can be used when it is required to create just one object of a class. As an example, if you have a ApplicationManager class in your application where all other components need to get help from, you need to have access to ApplicationManager object. But just think that you need to share some objects through your ApplicationManager. Then of course you do not want to have different object referring to different ApplicationManager objects. You need to have one common object shared with all of them. And singleton pattern is the way to achieve this.

I believe an example code snippet will help a lot in understanding this simply.

public class ApplicationManager {

    private static ApplicationManager applicationManager = new ApplicationManager();

    private ApplicationManager() { }

    public static ApplicationManager getInstance() {
        return applicationManager;
    public void yourMethod() {

So you see the constructor is private, so no one can initialize an object of ApplicationManager and if they want to use it, can call getInstance() method and use the already created static ApplicationManager object. So no more than one object is created and global access is provided.

Monday, October 5, 2015

Producer Consumer Pattern

Producer Consumer Design Pattern is one of the mainly used design patterns. And I am pretty sure that, many who does not know that this is an example of a design pattern too have used it. This design pattern is mainly used to introduce decoupling between consuming something and the relevant producing procedure. In other words it implements an efficient and smooth data sharing between the producer of the data and the data consumer. This decoupling is mainly done maintaining a queue for the data items.

By using a queue even the producer and consumer have different rates of producing and consuming data, the data sharing floor will be smooth through the queue. Producer do not have to wait until the consumer finishes data item 1 to deliver data item 2. And producer do not have any overhead of managing the produced items even though there are many consumers as far as all the consumers are consuming the items in that same queue.

So this design pattern can be easily used to perform data sharing between the producer parties and consumer parties in order to achieve good synchronization among them.

Importance of Design Patterns

Design Patterns is one of the most interesting topics in software development. They give well structured and standard solutions for solving common software implementation problems. To understand the design patterns, you should understand the problem that they solve. If you understand them, when you get some problem related to any of the design patterns you know, you can easily map the solution to your problem.

But if ‘Design Patterns’ is a new term for you even though you are doing good software implementation may be still you don’t have to worry. Because may be you are already using design patterns without knowing the correct terminology for those patterns. Still knowing them will help you a lot in improving your implementation as well as it will make it easy for others to quickly understand the functionalities of your implementation. And it will help a lot in smoothly communicating your solutions to the others. As an example if you say that you are using Factory method to solve problem X, others will just understand it without you explaining how you are doing it.

So Design patterns make your code handy, make it more readable and self explanative as well as will be helpful in smooth communication about your implementations.

Here are some commonly used design patterns

  • Producer Consumer    (Oh... You were using this right? That is why I added it first )
  • Singleton
  • Factory/Builder
  • Observer
  • Decorator
  • Command
  • Proxy
  • Strategy

Saturday, April 4, 2015

Avoid tracking your own page views

Are you interested in finding out the stats of your website? I am sure you do not need to count your own page views (if you like to see the true value). If you are using blogger, it gives a simple option for this. But unfortunately it did not work for me. It says " There was an error while fetching stats. Please reload page."
( you can try logging to your blogger account > Stats and click on "Don't track your own pageviews")

After some effort could find another solution that could fix my issue and here it is...

While been logged in to your account, open a new tab in the browser and enter


(make sure you replace the your_site.com with your site name)

You will get the following response
// API callback

Restart your browser and you can see that your page views are not counted in stats :)

Wednesday, April 1, 2015

Want to map your keyboard with the keyboard for your VM?

Recently I had to work in VMs for few of my projects and the biggest burden is the changes in keyboard. I am using a Mac and wanted to use Windows on a VM for a project. It is really irritating when you have to work in both environments interchangeably. You will definitely press cmd + c to copy in your windows VM and wonder why cmd + v won't work :O

I could find a simple solution for this with the help of autohotkey.
So this is how I map the Mac keyboard to Windows VM. ( and I am using VirtualBox)

Map the hostkey of the VirtualBox to right command key.

Start VirtualBox
Select VirtualBox > Preferences from the top menu

Input > Virtual Machine
Search for 'host key combination' and set the right command key for the key combination

Setup the VM to have changes

Download autohotkey to VM
Create a file in VM with extension .ahk ( ie: script.ahk )
Following is a sample content for the file with some of the most useful key mappings

#SingleInstance force
#r::Send ^r ;reload
#z::Send ^z ; undo
#y::Send ^y ; redo
#f::Send ^f ; find inside apps
#c::Send ^c ; copy
#x::Send ^x ; cut
#v::Send ^v ; paste
#t::Send ^t ; new tab, Firefox
#s::Send ^s ; save inside apps
LWin & Tab::AltTab ; the motherlode, alt-tab!
#b::Send ^b ; bold / bookmarks in Firefox
#i::Send ^i ; italic
#u::Send ^u ; underline
#a::Send ^a ; select all

Save the content and save the file.
Right click on file and do 'run as administrator' and you are ready to go... :)

Add the script to the Startup Programs

Add your file to Startup folder and you will have no issue with VM restarts...
Start > Program Files > Startup

Hope you will find your life with VMs much more easier with this.

Saturday, March 21, 2015

Need to run many instances of your project in visual studio?

Solution is simple.

Right click on your solution
Set Startup Projects
Select ‘Multiple startup projects
And select ‘Start’ option for your projects in the list.

And now when you hit start button, all the project you selected will be started.

Well, you need several instances of the same project to be started?
Right click on the project
Debug > Start New Instance

(This option will be useful to interestingly try out the Chat Application we developed previously. Because with more chat clients, it will be more interesting )

Friday, March 20, 2015

Building .NET Remoting sample (Step by Step)

I am new to .Net and for one of my projects I had to use .NET Remoting. It was bit hard to find an end to end sample for a beginner even though there are code snippets describing each functionality. So I felt that it will be useful to share this with you.

I am going to give step by step details so that someone who is not familiar with visual studio can also follow and build the sample without any issue. (I am going to use visual studio which is most widely used IDE for .NET)

.NET Remoting is a mechanism that is used to access the remote services across network. (If you are familiar with WebServices the requirement which Remoting fulfills is similar to a WebService. But Remoting works with remote objects)

We are going to implement a simple chat service using .NET Remoting. We will need to implement 3 modules for this. 
  • Shared Library
  • Server side implementation
  • Client side implementation 

Implementing Shared Library

We will first create the shared library because both the client module and the server module is going to need it.
The shared library is used to define the remote objects that one party is going to expose to the other party. In our chat example we will need a remote object that server expose to client which allows sending messages. And another object that client expose to server which allows receiving messages. (All this will be very clear when you start building the project, so don’t worry  )
So let’s start creating the project.
File > New > Project
Select ‘Class Library’ and give the name as ‘ChatLib’ in the field below.

We need to have 2 Interfaces for the two remote objects exposed by the server and client. So let’s create two classes ClientLib and ServerLib in our Chat lib project.

In solution explorer, right click on ChatLib
Add > New Item > Interface
And give the name for the interface in the textbox below. (In this sample I am going to use IService for the interface name)

Now add the methods that we are going to expose

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ChatLib
    public interface IService
        void register(string userName, string url);
        void sendMessage(string userName, string msg);

Create interface IClientService as same as above and add the method

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ChatLib
    public interface IClientService
        void receiveMessage(string sender, string msg);

Now you are done with the ChatLib component

Server Side Implementation

Now lets add the server side code. For this do right click on solution

Add > New Project > Console App
And give the name as ServerApp

The new project will be visible along with ChatLib under solution view.

Since we are going to have the implementation of the IService in this module we need to add ChatLib as a reference to our new project. To do that right click on ServerApp

Add Reference > Solution > Projects
Tick ChatLib project which is under Solutions > Projects

We need one more reference
Assemblies > Framework
Tick System.Runtime.Remoting

Here is the code for ServerApp (to make it easy I am going to add the whole code to one file here)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using ChatLib;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Tcp;

namespace ServerApp
    class Program
        static void Main(string[] args)
            TcpChannel channel = new TcpChannel(9443);
            ChannelServices.RegisterChannel(channel, true);
                "ChatServerService", WellKnownObjectMode.Singleton);

            System.Console.WriteLine("Server...... press any key");

    public class Server  : System.MarshalByRefObject, IService
        public Dictionary users = new Dictionary();
        public TcpChannel channel;

        public Server()
            channel = new TcpChannel();

        public void register(string userName, string port)
            users.Add(userName, port);
            Console.WriteLine("user added: " + userName);     

        public void sendMessage(string sender, string msg)
            Console.WriteLine("msg : " + msg + " received from " + sender);

            foreach(var item in users)
                //send msg to all clients 
                IClientService clientService = (IClientService)Activator.GetObject(typeof(IClientService),
                            "tcp://localhost:" + item.Value + "/ChatClientService");
                if (item.Key != sender)
                    clientService.receiveMessage(sender, msg);

Now as the same way you created the ServerApp, create another console application for the ClientApp too and add the same references (ChatLib and System.Runtime.Remoting )

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ChatLib;
using System;
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Tcp;

namespace ClientApp
    class Program 
        static string userName;

        static void Main(string[] args)
            Console.WriteLine("Enter username:");
            userName = Console.ReadLine();
            Console.WriteLine("Enter port:");
            string port = Console.ReadLine();

            Program program = new Program();

            Console.WriteLine("Now you can send messages");

        public void register(string port)
            TcpChannel clientChannel = new TcpChannel(Convert.ToInt32(port));
            ChannelServices.RegisterChannel(clientChannel, true);

            ClientService clientLib = new ClientService();
            RemotingServices.Marshal(clientLib, "ChatClientService", typeof(ClientService));

            IService service = (IService)Activator.GetObject(typeof(IService),

            service.register(userName, port);

        public void sendMessage()
            IService service = (IService)Activator.GetObject(typeof(IService),
            while (true)
                string msg = Console.ReadLine();
                service.sendMessage(userName, msg);

    public class ClientService : MarshalByRefObject, IClientService
        public void receiveMessage(string sender, string msg)
            Console.WriteLine(sender + " : " + msg);

OK... You are done with your chat application with .NET Remoting. Now you can run the application and see.

Sunday, March 8, 2015

I love Traveling...

Sri Lanka (Home Country)
Idaho (US)
Seattle (US)
Vatican City

Thursday, February 19, 2015

Changing font style in Tumblr posts

Tumblr is a simple and nice microblogging site. I wanted to use it for very short posts which I think are important. But when I started using Tumblr for this I felt that the font size of the posts are bit bigger. ( This may not be the case if you create posts with a considerable content. But it my case I mostly wanted to post few lines of posts, so the title of the posts looked bit bigger than expected)

I could not find a simple setting to change the font size of the post titles, but I could find a simple way  to do that by editing the html code.

1. Go to the home page of your Tumblr account and click on 'Customize' menu

2. In the left side panel, select 'Edit HTML'

3. Search for 'block:Posts' section in the html code. (use ctrl + f to get the search box )
Then you can see the 'block:Title' section in that. You can add the font style that you need for the title of the posts in that section.

4. You can use 'Update Preview' button and see how the new font style looks like.
Make the changes you need and hit 'Save' and you have what you need.

Sunday, January 25, 2015

Issue in put files to hadoop - 0 datanodes running

I setup hadoop as I have described in my previous posts. While I was working in some interesting projects on Map-Reduce, I faced an issue on sending some of my local files to the hdfs node. I have started dfs already, but exception says
14/10/25 17:46:20 WARN hdfs.DFSClient: DataStreamer Exception org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /user/ashansa/input._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 0 datanode(s) running and no node(s) are excluded in this operation. at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget(BlockManager.java:1471) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2791) at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:606) at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:455) at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java) at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585)
I faced this issue several times, so I think it will be helpful if I tell you how to overcome this issue. ( I believe this is a common issue we get while running hdfs, since I got the same issue several times and I found that many others also have faced the same issue )

What worked for me?

1. Stop the hadoop cluster with

2. Clean hadoop tmp directory
    You can find the path to your hadoop tmp directory in hdfs-site.xml.
    Check for the following tag in hdfs-site.xml file.
    You can find the path to your hadoop temp directory in <value> tag.

3. Format node
             bin/hadoop namenode -format

4. Start hadoop cluster

With these few simple steps, I was able to overcome this issue.
Hope this will help you too.