Posts

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.

Do not delete [] a scalar pointer !!!

Recently I got tangled into this problem in my code - Calling a vector destructor for a scalar pointer. We all know that it is perfectly illegal to do that. For example, if we allocate something like this:-

OurClass *p = new OurClass();

and try to delete like this:-

delete []p;

then we are going to end up in trouble. Of course, we know that we will end up in trouble. But I have really not given a thought WHY!

Where do you QueryInterface ???

For an ATL class, the QueryInterface is implemented in CComObject. The figure below is the inheritance hierarchy for a class generated by the wizard representing an ATL-COM object.

CComObjectRootBase has an InternalQueryInterface method, which uses the interface map built by the BEGIN_COM_MAP macro to resolve IID -> interface pointer. The BEGIN_COM_MAP macro also defines a method _InternalQueryInterface, which passes the map on to InternalQueryInterface. CComObject implements QueryInterface, and calls _InternalQueryInterface.

Use Of Class Factories !!!

To understand quickly and to explain in the simplest way, Class Factories are the factory classes that create a COM object. A class factory may be responsible for creating one or more COM objects. In the case of COM OutOfProc servers, the server registers the class factories for objects that it can create in a system-global table using CoRegisterClassObject. Whenever a client does CoGetClassObject for a CLSID, the COM run-time can look it up in the system global table, and return the factory instance. The case with InProc servers is also similar but through the DLLGetClassObject. More ...