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Showing posts from April, 2006

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: [DllImport("ole32.dll")] private static extern int CoRegisterC…

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.

GraphicsPath windowShape = new GraphicsPath();
windowShape.AddEllipse(0, 0, 320, 200);
this.Region = new Region(windowShape);

The GraphicsPath has methods to create wiondows of other shapes too.

I am not sure but I think it was not this straight forward in the MFC/Win32 programming world. Thanks to C#.NET. I love this 3 lines of code.

Serialization and Exceptions !!!

I am just in a stage 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 that said "The constructor to deserialize an object of type MyException was not found". But I had the Serializable attribute tagged to my custom expection class.

Let me to get to the point. Even though you attach the Serializable attribute to your custom exception class, the base class Exception implements the ISerializable interface and the constructor required during the deserialization [Exception()] is protected. So when you throw MyException, it may get serialized and cross the remoting boundaries but on the client side, it will not able to deserialize because …

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 constrcution 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 initialze 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.

I do not recommend putting the initializa…

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.

The interesting thing is that for the following code, the compiler spits an error saying "'System.Collections.IDictionaryEnumerator.Value' cannot be assigned to -- it is read only":-
IDictionaryEnumerator de = ht.GetEnumerator();
de.Value = null;
} while for this code
foreach(string key in ht.Keys)
ht[key] = null;
}it compiled successfully but threw a runtime exception [An unhandled exception of type 'System.InvalidOperationException' occurred in mscorlib.dll Additional information: Collection was modified; enumeration operation may not execute].

But the solu…

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 app…

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.

But I was in the same situation and my head had stopped working and my hands went coding the same way, and found that it does not work. In C#, i have the facility to declare a interface and by default its methods are public, strictly no need of any access specifiers. And the class that implements has to implement it publicly. So my O…

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 …

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:-

__property bool get_LogToStdError()
return logToStdError;
__property void set_LogToStdError(bool value)
logToStdError = value;

Doesn't that seem like the cat scorching its skin wanting to look like a tiger ? But we need to understand that the Managed C++ is just an extension provided by Microsoft for C++, and is not standard unlike C++/CLI. And then in C++/CLI, the syntax for property was reformed …

Managed Debugging Assistant !!!

The Loader Lock is a synchronization object that hepls 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 the some dll load code is executed, the loader lock is set and after the complete intialization 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 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.

For instance, if an unmanaged DLL's DllMain entry point tries to CoCreate a managed object that has been exposed to COM, then it is an attempt to execute managed code inside the loader lock.

MDA - Managed Debug…