Posts

CComPtr Misconception !!!

This is about a killer bug identified by our chief software engineer in our application. What was devised for ease of use and write smart code ended up in this killer defect due to improper perception. Ok, let us go!

CComPtr is a template class in ATL designed to wrap the discrete functionality of COM object management – AddRef and Release. Technically it is a smart pointer for a COM object.

OrderedThreadPool – Task Execution In Queued Order !!!

I would not want to write chunks of code to spawns threads and perform many of my background tasks such as firing events, UI update etc. Instead I would use the System.Threading.ThreadPool class which serves this purpose. And a programmer who knows to use this class for such cases would also be aware that the tasks queued to the thread pool are NOT dispatched in the order they are queued. They get dispatched for execution in a haphazard fashion. More ...

Settling Casting Restrictions

Remember the Casting Restrictions we discussed a while back, let us settle that now. So we have some code like this:

object obj = i;
long l = (long)obj;

And an invalid cast exception while casting ‘obj’ to long. It is obvious that we are not changing the value held by obj, but just reading it. Then why restrict such casting. Let us disassemble and see what we got.

.locals init (
  [0] int32 i,
  [1] object obj,
  [2] int64 l
)
L_0000: nop
L_0001: ldc.i4.s 100
L_0003: stloc.0
L_0004: ldloc.0
L_0005: box int32
L_000a: stloc.1
L_000b: ldloc.1
L_000c: unbox.any int64
L_0011: stloc.2
L_0012: ret

Oh, there we see something interesting - unbox. So the C# compiler uses the unbox instruction to retrieve the value from obj while casting; it does not use Convert.ToInt64 or similar mechanism. That is why the exception was thrown.

The WD Anti-Propaganda Campaign !!!

Thanks to the internet. If nobody else bothers or understands what loss of data means, you can shout it aloud here. I lost 500GB of data - every moment of my personal and professional life captured in bits and bytes.

It is a Western Digital Premium Edition external hard disk (USB/Firewire). I bought it despite my friend warning of bad sectors and hardware issues that WD is known to have. As with any story, one fine morning, I was copying some songs, pictures from my pen drive to the hard disk. All of a sudden, the hard disk and my laptop hung up. I restarted the system thinking I would make fresh start. But to my dismay, all my drives on the hard disk had vanished like dust. I tried connecting and reconnecting a few times, the drives showed up once or twice like a sick man’s last few breadths.

Casting Restrictions ???

We all know that the runtime can detect the actual type of a System.Object instance. The primitive data types provided by the runtime are compatible with one another for casting (assuming that we do not truncate the values). So if I have an int, it can be cast to long or ulong. All that is fine. Watch this:-

interface IAppDataTypeBase
{
   // Other methods
   GetValue();
}

Since IAppDataTypeBase represents the mother of all types of data in my application, I have made GetValue to return the value as object (I could have used generics, that is for another day!).

Understanding (ref)erences

Let us take a look at the following piece of code:-

public void Operate(IList iList2)
{
 iList2 = new List();
 iList2.Add(1);
 iList2.Add(2);
 iList2.Add(3);
}

public static void Main()
{
 IList iList= new List();
 iList.Add(10);
 Operate(iList);
 Console.WriteLine(iList[0].ToString());
}

Be thinking about what would the above program print to the console ? And that is what we are going to talk about in this post – simple but subtle.

Extension Methods – A Polished C++ Feature

Extension Methods is an excellent feature in C# 3.0. It is a mechanism by which new methods can be exposed from an existing type (interface or class) without directly adding the method to the type. Why do we need extension methods anyway ? Ok, that is the big story of lamba and LINQ. But from a conceptual standpoint, the extension methods establish a mechanism to extend the public interface of a type. The compiler is smart enough to make the method a part of the public interface of the type. Yeah, that is what it does, and the intellisense is very cool in making us believe that. It is cleaner and easier (for the library developers and for us programmers even) to add extra functionality (methods) not provided in the type. That is the intent. And we know that was exercised extravagantly in LINQ. The IEnumerable was extended with a whole lot set of methods to aid the LINQ design. Remember the Where, Select etc methods on IEnumerable. More ...

The Surprising Finalize Call

Guess the output of the following program:-

class SomeClass : IDisposable
{
  public SomeClass()
  {
		Trace.WriteLine("SomeClass - Attempting instance creation");
		throw new Exception("Ohh !!! Not Now");
	}

	public void Dispose()
	{
		Trace.WriteLine("SomeClass::Dispose");
	}

	~SomeClass()
	{
		Trace.WriteLine("SomeClass::Finalizer");
	}
}

int Main(string args[]){
	try{
		SomeClass sc = new SomeClass();
  }
	catch(Exception ex){
		Trace.WriteLine("Main - {0}", ex.Message);
  }
}

This will be the output of the program:-

Learning Type Access Modifiers Basics

When I started developing my module, I had an interface IParamCountBasedAlgo declared as a nested type in a class AlgorithmOneExecutor, declared as follows:-

namespace DataStructuresAndAlgo
{
   partial class AlgorithmOneExecutor
   {
      private interface IParamCountBasedAlgo
      {
         void Validate();
         void Execute();
      }
   }
}

First Google Gadget(s)

I did some cool stuff here with google. I wrote my first “Hello World” sort of google gadget. It claims no rewards but just was fun. Since I am a novice in html and javascript sort of things, this gadget is pretty simple.

Use the following URL to enjoy the gadgets.:

• Pirate.xml
• Clock.xml