Posts

Implementing COM OutOfProc Servers in C# .NET !!!

Had to implement our COM OOP Server project in .NET, and I found this solution from the internet after a great deal of search, but unfortunately the whole idea was ruled out, and we wrapped it as a .NET assembly. This is worth knowing.

Step 1

Implement IClassFactory in a class in .NET. Use the following definition for IClassFactory.

namespace COM
{
   static class Guids
   {
      public const string IClassFactory = "00000001-0000-0000-C000-000000000046";
      public const string IUnknown = "00000000-0000-0000-C000-000000000046";
   }

   ///
   /// IClassFactory declaration
   ///
   [ComImport(), InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid(COM.Guids.IClassFactory)]
   internal interface IClassFactory
   {
      [PreserveSig]
      int CreateInstance(IntPtr pUnkOuter, ref Guid riid, out IntPtr ppvObject);
      [PreserveSig]
      int LockServer(bool fLock);
   }
}

Step 2

Non-conventional Window Shapes [I love C#] !!!

I am not a UI guy. More specifically, I love to work with UIs. I think (only) a UI can give a better picture of the system in a multitasking environment unlike Unix. I do not say I hate Unix. And I do not like to work on UIs ie program on UIs cuz I do not know much. But have always wanted to create a non-conventional window, say an elliptical one. .NET made things like that very easy for guys like me. Look at the code below for creating a ellipitcal window. More ...

Serialization and Exceptions !!!

I am just like Alice in Wonderland, and not yet got out of the wonders of the .NET framework, C# and the VS 2003(5) IDE. I thought that the serialization is all not my thing until I do something big in C#. I had written this custom exception class in my project that has 3 processes connected by .NET Remoting Infrastructure. I throw my custom exception for a scenario but all I got was some other exception: More ...

Know where you initialize and Do not forget to uninitialize !!!

If you have long been programming in C++/COM and then you move to C#.NET, the first difference you can feel is that you got a ctor for the object you create unlike the CoCreateInstance. In the C++/COM world, you generally would have a Initialize method to do the construction sort of, paired with Terminate/Uninitialize method. Similar is the case with singleton classes. For singleton classes in C++, you will have public static Instance or GetInstance method to get the only and one instance of the class and then use the initialize method to do the construction. This is certainly advantageous than the ctor facility in .NET, since you will not know when the instance will be initialized without the initialize method. Any call like SingletonClass.GetInstance().SomeMethod may initialize the singleton anywhere and you will not exactly do the initialization during the application startup, which in many cases will lead to application errors after startup. More ...

An encounter with Hashtables !!!

I encountered a situation like this where I had a hashtable in which the key is a string and the value is some object, and I had to change the values of all the keys [from zero to count] to null or some other value. I used the some of the facilities – enumerator, the Keys property etc provided by the hash table itself but it did not work out, and I spent too much time on this. More ...

A Note On Finalize !!!

This is not about what Finalize is, but well Finalize is the last call on a managed object, where you can perform some clean up operations, before getting garbage collected by the .NET runtime. A few important things that are to be noted about finalizers are:-

• In C#, finalizers are represented by the ~ClassName [destructor syntax], and the Object.finalize can neither be overridden or called directly. It cannot be called directly because it is protected. The destructors in C# also take care of calling the dtor of the base class.
• Finalizer is called on an object only once, just before the .NET runtime attempts to garbage collect the object.
• Finalizers can be called anytime on a managed object that is not being referenced, and on any thread by the .NET runtime.
• The order in which the finalizers are called is also not fixed. Even when two objects are related to each other in some way, there is no hierarchial order in which the finalizers for the objects will be called.
• During an application shutdown, finalizers will be called even on objects that are still accessible.

The most interesting part of the finalizer is not when it is called but when all is it NOT called. This is where we need to watch and rely on the Dipose method IDispoable - Dispose pattern¹.

Explicit Interface Implementation !!!

I have encountered this [wait i’ll explain] sort of situation many times and I mostly do this way in C++.

Assume you have a class CMyClass that exposes its functionality through its public methods, and also let it listen to events from some sources, events being OnSomeEvent or OnXXXX(), by implementing some event interface IXModuleEvents. Now these event listener methods are reserved only for internal use and are not meant to be called by the users. So when I implement the IXModuleEvents interface in CMyClass, I make them private. Think about it and the problem is solved. It is the polymorphism game, that never cares for the accessibility of the method.

The Interface Based Programming Argument !!!

I am always a great fan of interface programming. I mean not exactly the interface keyowrd but some way to expose the functionality of the class or your module relieving the user about the worries of the implementation. But definitely make him curious of the stuff inside.

The Win32 APIs are not that good in what I am talking about. Well, there are several reasons for that. And I strongly object that they are raw APIs and not for the ordinary application programmer. That kind of an abstraction is there at every level. Even a programmer using the Win32 APIs does not know what goes inside though some of the APIs expose unknowningly the sort of internals. This is an argument, but what I mean to say is that anything that you wish your users to use must have a elegant interface just exposing the functionality, and in the most intuitive way that makes sense. It may be an interface in C# or an abstract class in C++. And once you do that, you will slowly be under the tree where you can clearly realise the roots of an object oriented system.

Properties in C++/CLI - The C# look alike

Inherently after writing some code in C#, I wanted everything to be as easy to do like in C#. And could not resist myself writing property like syntax in C++ [ofcourse C++/CLI, threw away the ugly Managed C++ before it was too late for my code to grow into a tree]. Then I learnt that properties are supported in C++.NET too but as always in the ugly way. But in C++/CLI, I was happy enough that the syntax is more elegantly redefined. For instance, there was this boolean member logToStdError in my class, and in my legacy code, the property definition for logToStdError looked like:- More ...

Managed Debugging Assistant !!!

The Loader Lock is a synchronization object that helps to provide mutual exclusion during DLL loading and unloading. It helps to prevent DLLs being re-entered before they are completely initialized [in the DLLMain].

When some dll load code is executed, the loader lock is set and after the complete initialization it is unset. But there is a possibility of deadlock when threads do not properly synchronize on the loader lock. This mostly happens when threads try to call other Win32 APIs (LoadLibrary, GetProcAddress, FreeLibrary etc.) that also require the loader lock. Often this is evident in the mixed managed/unmanaged code, whereby it is not intentional but the CLR may have to call those APIs like during a call using platform invoke on one of the above listed Win32 API.