Links : What is REST?

I needed to learn about REST interface and wanted some good article for learning basics of REST : REpresentational State Transfer. This article : A Brief Introduction to REST is really the best one I found so thought of sharing it with you. REST is really nice idea of further simplifying the modeling of web-applications. I implemented by REST program with JSON and my client is in Javascript which is really cool (People are writing entire web based OS and here i am playing with simple java script stuff :-) ) With help of java-script libraries you can easily achieve data binding : like FLEX and other RIA. I really enjoyed working with this totally different stuff. I will add snippets in coming days.

..
Tushar

Links : Things I Wish I’d Been Told

When I look back in my engineering days and now, I certainly figured out one thing : Whatever they teach in class hardly matters - the syllabus is totally outdated. What matters is that how you learn new things quickly, be updated in this fast moving world of technology.

Here I am sharing a link I Wish I’d Been Told, when I graduated with computer science engineering degree. Tips For Students with a Bachelors in Computer Science

Funny Tech Videos : Part 5

Geeky Valentine .. for bloggers and twiters.



Happy Valentine Days May all you get linklove that you deserve.


..
Tushar

Download Your Favorite Youtube Videos in Batch

Last week SRGMAP - LC ( Sa-Re-Ga-Ma-Pa Marathi Little Champs) singing contest for children finished. These children are really are talented and boy, crowd loved every performance from them. From long time this was the only show that I wanted to watch every episode of it and did not miss much initially. But when I moved out for my job I was missing it but then this guy "ahonkan" made sure i at least get to see performance of these god gifted children. Thanks a million ahonkan .. there will countless others like me. Now competition is over I thought of downloading all videos and keeping copy of it for as my personal collection. Initially I thought I will write my small program in java where I will download the user specific feeds, playlists, Chanel and the via youtube API i will download all FLV files. But then I did came across this great program. : 1-Click Youtube Downloaded. It allows you download and match bunch of videos It allows you donwload and match bunch of videos from youtube.

Below is the video from 1-Click which shows you how to download videos using this program.



great stuff. may be older but still good enough for another word in blogo-sphere.

Note : Videos uploaded on youtube could be subject to copyright and may be illegal. Here I am only writing about the useful computer program. Make sure you know what you are downloading. Thanks

Tushar

Funny Videos Part 4

Here is another tech video : She's An Engineer, soft song

Could not grasp entire lyrics but here is some part of first para.

Ah the way I'm feeling now we could lick the world
cause you know I'm always dreaming about you girl
I've been testing out your structure and found it sound
Been installing all our circuits on solid ground
Ah the way I'm feeling now we could take it on
Turn it in our favor and get it on
Generating answers and getting speed
You've got to run it with the fun of it and take it cause
She's an engineer
We don't have much to fear
Ghost in the computer
Ghost goes in sie puter

Free Collaboration Software : Mikogo

I just used free collaboration software Mikogo. At work place I used WebEX : the default choice but at home I needed to collaborate : basically share screen, show some demos, slides. With content sharing you also need to speak : i used skype for that. For screen sharing I searched google and Mikogo was the first result. It the on of the nest free software I have encountered : No hidden features, nearly all of features : like giving control to other participants, see other participants screen are present.
It also has integration with skype which i did not used but will use for my next meeting. I initially assumed there will be some cap on either on duration on participants but our meeting well last 2 and half hours. In fact we spent 10 minutes in finding and testing out features of Mikogo.

Who needs WebEX? certainly for personal Mikogo is the best.

..
Tushar

CountDownLatch for Terracotta

With Java 5, java has inbuilt concurrency library in java.concurrent with classes like CountDownLatch, CylcicBarrier, FutureTask, ExecutorService, LinkedBlockingQueue, ConcurrentHashMap, ReentrantReadWriteLock, which greatly simplifies writing multi-threaded applications. With increasing number of cores you need to write applications which are multi-threaded. With Terracotta this further makes really simple to run such application across more than one JVM effectively giving you more number of threads with slight degradation of performance but near-linear scalability. Terracotta supports some important data structures of "java.utl.concurrent" out of the box these are mainly : LinkedBlockingQueue, ExecutorService, CycliBarrier., FutureTask and of course Locks.


Below I am presenting one more addition to this library : CountDownLatch. CountDownLatch is used to co-ordinate between threads. You pass number of threads in constructor and each thread then calls countDown() method. When you want to get notified that all threads have finished their work you call await() method. This method will wait till all parties have finished and called countDown() method. If you want to write such code in Terracotta enabled applicaiton you have to use CyclicBarrier where each thread calls await() method. But this will cause finished threads to unnecessarily block on barrier. By using CountDownLatch you can "countdown" and exit the thread thus only master or co-ordinator thread needs to block.

Logic implemented is very simple - initiate with number of parties. decrease the counter in countDown method, when reached to zero notify all waiting threads and in await() method "wait()" on object till count is reached to zero.

Below is the source code for it. You need to put class MyCountDownLatch in instrumented classes section as well as define write-lock for the await() and countDown() method. You can download the source-code for the same here.


Main Class

public class MyCountdownLatch {

	

	

	int count = -1;

	public MyCountdownLatch(int count)

	{

		this.count = count;

	}

	

	

	public synchronized void countDown()

	{

		count--;

		if (count == 0) { notifyAll();  }

	}

	

	

	public synchronized void reset(int count)

	{

		this.count = count;

	}

	

	public synchronized void await() throws InterruptedException 

	{

        if (count == 0) { notifyAll(); return; }

        else { 

        	while(count > 0)

        		{

        			wait(); 

        		}

        }

	}



}

Test Class TestCountDownLatch

import java.util.Random;



public class TestCountDownLatch {

	

	public static int N=10;

	

	public static MyCountdownLatch startSignal = null;;

	 public static MyCountdownLatch doneSignal = null;	

	

	 private static Object lock = new Object();

	 

	public static void main(String[] args) {

		

		

		Runnable runs[] = new Runnable[N];

		

		if(startSignal==null)

		{

			synchronized (lock) {

				startSignal = new MyCountdownLatch(1);

				doneSignal = new MyCountdownLatch(N);	

			}

		}

		

		

		 for(int i=0;i		 {

			runs[i] = new Worker(startSignal,doneSignal);

			new Thread(runs[i]).start();

		 }

		 

		 startSignal.countDown();

		 try {

			doneSignal.await();

		} catch (InterruptedException e) {

			

			e.printStackTrace();

		} 

		

		

		System.out.println("All thread finished ...");

		

	}

	

	

	public static class Worker implements Runnable

	{

		MyCountdownLatch startSignal = null;

		MyCountdownLatch doneSignal = null;

	

		public Worker(MyCountdownLatch startSignal, MyCountdownLatch doneSignal)

		{

			this.startSignal = startSignal;

			this.doneSignal = doneSignal;

			

		}

		

		public void run()

		{

			System.out.println("Waiting for start signal...");

			try {

				startSignal.await();

			} catch (InterruptedException e) {

				

				e.printStackTrace();

			}

	        doWork();

	        doneSignal.countDown();

		}

		

		public void doWork()

		{

			System.out.println("Starting to work now");

			Random random = new Random();

			try {

				Thread.sleep(random.nextInt(2000));

			} catch (InterruptedException e) {

				// TODO Auto-generated catch block

				e.printStackTrace();

			}

			System.out.println("Completd work");

		}

		

	}

	



}

Config file tc-config.xml

<?xml version="1.0" encoding="UTF-8"?>

<tc:tc-config xsi:schemaLocation="http://www.terracotta.org/schema/terracotta-4.xsd" xmlns:tc="http://www.terracotta.org/config" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

  <servers>

    <server host="localhost" name="tc-srv01" bind="0.0.0.0">

      <data>%(user.home)/terracotta/server-data1</data>

      <logs>%(user.home)/terracotta/server-logs1</logs>

      <dso-port>9510</dso-port>

      <jmx-port>9520</jmx-port>

      <l2-group-port>9530</l2-group-port>

      <dso>

        <garbage-collection>

          <enabled>true</enabled>

          <interval>300</interval>

          <verbose>true</verbose>

        </garbage-collection>

      </dso>

    </server>

  </servers>

  <clients>

    <logs>%(user.home)/terracotta/client-logs1/</logs>

    <statistics>%(user.home)/terracotta/server-statistics-%D</statistics>

  </clients>

  <application>

    <dso>

    <instrumented-classes>

        <include>

          <class-expression>*..*</class-expression>

        </include>

      </instrumented-classes>

      <roots>

        <root>

          <field-name>TestCountDownLatch.startSignal</field-name>

        </root>

        <root>

          <field-name>TestCountDownLatch.doneSignal</field-name>

        </root>

      </roots>

      <locks>

        <autolock>

          <method-expression>* MyCountdownLatch.countDown(..)</method-expression>

          <lock-level>write</lock-level>

        </autolock>

        <autolock>

          <method-expression>* MyCountdownLatch.await(..)</method-expression>

          <lock-level>write</lock-level>

        </autolock>

      </locks>

    </dso>

  </application>

</tc:tc-config>