Pre-requisites: Cygwin with Python & some additional packages (we’ll go over that in a bit)

1. Double click Cygwin’s setup.exe and continue till you get to select packages window
2. Select Python



3. Select Make



4. Select G++



5. Select wget(not really required but, good to have for downloading archives & stuffs )



6. Click next and complete the installation
7. From cygwin type the following commands. Note: At the time of this writing v0.2.0 is the current NodeJS version.

   			wget http://nodejs.org/dist/node-v0.2.0.tar.gz
   			tar xvf node-v0.2.0.tar.gz
   			cd node-v0.2.0/
   			./configure
   			make
   			make install
   		

8. If all goes well, then you should see NodeJS’s version when you type the following command.

   		node --version
   		v0.2.0
   		

Now its time to crack some code to your heart’s desire

As you might know already, the following code snippet throws StackOverflowError.

	public class StackOverflowTest {
		public static void main(String[] args) {
			main(args);
		}
	}
  

If you read the javadoc of StackOverflowError, it says that error happens when application “recurses too deeply”. There are two key words to underline here… “recurse” and “deep”. The word recursion according to google (Did you mean: recursion ) & programmers lingo, some method calling itself. So, it’s very natural to think StackOverflowError happens only when we run into this inifinite recursion scenario. But, thats not entirely true. It could also happen when we have method call chain which is “too deep”.

So, in order to find out how deep is “too deep”, I wrote this code snippet. Obviously, it will vary between different JRE versions, OS etc and you can also increase the stack size limit by setting -XX VM param.

In order to prove the stack overflow in “non-recursion” scenario, here is a Java code that will create, compile & run Java code with nested method call chain of limit set to 7000.

So, if you think this little more deeper, someone like me would wonder.. Is it a limitation that a Java class/application cannot have more than certain number of methods? If yes, how does all the enterprise class software products written in millions of lines of Java code working? The answer to that question is… Yes, it is a limitation, but in only one thread. So, almost any enterprise/mid range Java project/product cannot be written in such a way that it would run in only one main thread and if it written that way, this is the limit you hit.

So, if we come back to our original problem and see if we can make it run. Here is how…

		public class StackOverflowLimitWithThreadTest {
		  private static int recursionLimit = 0;
		  public static void main(final String[] args) {
			new Thread(new Runnable(){
			  public void run() {
				System.out.println("recursionLimit++ = " + recursionLimit++);
				main(args);
			  }
			}).start();
		  }
		}
  

Here is the code snippet I came up with. In case if you have something that you like to share, feel free…

		public class Life {
		  public static void main(final String args[]) {
			boolean havingKids = args.length > 2;
			if (havingKids) {
			  System.out.println("Life is about to change forever...");
			  throw new LifeChangingException("Congratulations, " +
				"you are going to discover yourself.... Have fun along the way!!!");
			}
			main(args); //Sometimes you'll wish you are here
						// inspite of StackOverflow:)
		  }
		}

What you think?

So, What else is coming Google? Telling me who my real friends & foes are…:)

The intent of this article is to crash a JVM either “gracefully” or “non-gracefully”. It does not only mean JVM dying due to fatal errors.

If you can make it, then you should know how to break it. I think its more applicable to software systems than anything else. Being Java developers, we occasionally see JVM crashing either because we do something really silly or probably due to system’s limitation(bug, memory, threads etc.). But I was wondering, if I want to crash a JVM deliberately, what is the easiest way? In other words, with less line of code.

How “easy” is to crash a JVM? I am not talking about killing the process from Task Manager or running kill command in Unix .

Here are some of the options I came up with. If anyone can think of more “creative” ways, feel free to share it on the comments.

1.) JVM crash due to StackOverflow.

	public class JVMCrashTest {
		public static void main(String[] args) {
			main(args);
		}
	}
  

Exception in thread “main” java.lang.StackOverflowError

2.) This one will fail due to memory not being enough. We can use the same technique with data types other than Integer.

	public class JVMCrashTest {
		public static void main(String[] args) {
			Integer integers[] = new Integer[Integer.MAX_VALUE];
		}
	}
	

Exception in thread “main” java.lang.OutOfMemoryError: Requested array size exceeds VM limit

3.) This technique is very similar to the second one. Again, this approach can be tried with other data structures also.

	import java.util.*;
	public class JVMCrashTest {
		public static void main(String[] args) {
			ArrayList list = new ArrayList();
			for (int i = 0; i < Integer.MAX_VALUE; i++) {
				list.add(new Object());
			}
		}
	}
	

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

We constructively crashed the JVM, so now what?. Let's talk little bit about these approaches. Option 1 is very simple(less code) and my most favorite. It got into my thinking little more than how JVM can be crashed, possibly hinting some limitations which I never thought of before. But, I am going to save that discussion for a separate topic of its own.

Option 2 & 3 are very similar which may be fixed by adding more memory. In the meanwhile, if anyone can add more to this list, it will be great.

Note: The above code was run using JDK 1.6.0_18's JVM with the default memory settings.

I should admit WordPress installation was a breeze and I am quite impressed with its UI & overall design. Needless to say, it has whole bunch of themes & plugins if you want to do more with it. In my opinion, RoR doesn’t seem to be a stable or robust platform compared to PHP based frameworks.

1. Close the browser in both the machines
2. Backup C:\Documents and Settings\your_user_id\Local Settings\Application Data\Google\Chrome\User Data to C:\Documents and Settings\your_user_id\Local Settings\Application Data\Google\Chrome\User Data_Backup in Machine Y
3. Copy C:\Documents and Settings\your_user_id\Local Settings\Application Data\Google\Chrome\User Data from Machine X to C:\Documents and Settings\your_user_id\Local Settings\Application Data\Google\Chrome\User Data in Machine Y
4. Boom… Open chrome in Machine Y & make sure you have everything that you had in Machine X.

FYI – I have tested this in Windows XP Chrome Dev Channel 5.0 versions.

Update: I have tried this in Ubuntu machines and also between Windows XP & Ubuntu 9.10 and it worked fine. Replace the above folders with this one for Linux machines – /home/your_user_id/.config/google-chrome/Default

Right there I see some opportunity for developing a Chrome extension. If I get sometime and Google or anyone else didn’t come up with something for this, I might crack up some extension to do this automatically.

I have 5 years warranty on this drive. I called the manufacturer and talked to them about my case. They are ready to replace the drive, obviously not the data. So, what is gonna happen to my almost 1 TB worth of data? I started looking up online to see how I can rescue data from this drive. I tried many of Windows & Linux based tools. But, none of them helped me recover any data at all. I guess, the drive is damaged heavily and none of the recovery tools could do any good.

Here are some of the things to consider…

If I am going to have a backup/external drive, I would go for RAID based drives, preferably with RAID 1 or RAID 5 settings. And, I need to pro-actively perform periodic health checks on the external drives just to make sure its not gonna have heart attack or brain damage soon. May be it’s not a good idea to go for a huge capacity like >= 2 TB in a single drive, because of limitations on hardware storage machanism working within a confined physical limits.

In this digital world of inexpensive electronics & technologies, we trust so much on them in our day to day life. At some point in time, what we have in those are worth much more than 1′s and 0′s to us, personally.

I was working on a codebase in Windows machine where we have very very long file names. As you may know, Windows XP don’t support file names longer than 260 characters. It was very annoying when a maven build fails due to the file name length limitation. So, I wanted to write a script which can recursively loop through the project codebase and list out the files which exceeds certain length limit, so I can work on shortening their names. I could write that script in different ways like batch script, shell script, groovy script etc. But, I just wanted to write it in plain simple JavaScript and see how it plays.

If you want to try out the script. Copy the following code block in a JS file (For ex. FileNameLengthChecker.js).

/*
 Simple utility script to look for file names exceeding certain length restriction.
 (esp. for Windows XP - http://msdn.microsoft.com/en-us/library/aa365247(VS.85).aspx#maxpath).

 If you want to run check for a folder other than the current folder, change the value of
 rootDir variable.
 */

var filenameLengthThreshold = 260;
var headerPrinted = false;
var totalFilesFound = 0;

function runFileNameLengthCheck() {
    var rootDir = new java.io.File(".");
    echo("Checking file name length check in '" + rootDir.getCanonicalPath() + "' for threshold limit = " + filenameLengthThreshold + " ...");

    checkFilePathRecursively(rootDir);

    if (!headerPrinted) {
        echo("\n----------------------------------------------------");
        echo("No files found with the given threshold limit !!!");
        echo("---------------------------------------------------");
    }
    else {
        echo("Total files found = " + totalFilesFound);
    }

}

function printHeader() {
    if (!headerPrinted) {
        echo("\n------------------------------------------------");
        echo("Following files exceeded the file name length check...");
        echo("------------------------------------------------");
        headerPrinted = true;
    }
}

function checkFilePathRecursively(currentFolder) {
    var files = currentFolder.listFiles();
    for (var i = 0; i < files.length; i++) {
        if (files[i].isDirectory()) {
            checkFilePathRecursively(files[i])
        }
        else {
            var path = files[i].getCanonicalPath();
            if (path.length() > filenameLengthThreshold) {
                printHeader();
                echo("Filename = '" + path + "', length = " + new java.lang.Integer(path.length()));
                totalFilesFound++;
            }
        }
    }
}

runFileNameLengthCheck();

The simplest way to run the script file from a command line is through jrunscript tool bundled within JDK.

	C:\ProjectCodeBase\jrunscript FileNameLengthChecker.js

If you use IntelliJ IDE and Script Monkey plugin installed, you can directly run the script from IDE.

This is just a trivial example, but the possibilities of what we can do using the same technique is endless. Thoughts? Comments?

Often times, I tend to have heated discussions with my friends & colleagues regarding open-source software and how it changed the software development industry & information technology overall. I try explaining the evolution & significance of open-source community, standards & software and without which we wouldn’t have been in a place, where we are in the information technology today. There are tons of examples to quote ranging from Linux, Apache, Java etc. etc.

But, unfortunately not every big companies realise the importance of open-source sofware, atleast not from a giving-end perspective. It’s a cliche to say that every companies will be using open-source software either directly or indirectly. But, how many of them would be actively participating or contributing to the open-source community. I think that should grow.

Open source is not altruism, it is a culture to drive innovation and promote better competition. I am glad that article discusses breadth & depth of open-source both from technical & business perspective.