Introduction
What is an IL?
(IL)Intermediate Language is also known as MSIL (Microsoft Intermediate Language) or CIL (Common Intermediate Language). All .NET source code is compiled to IL. IL is then converted to machine code at the point where the software is installed, or at run-time by a Just-In-Time (JIT) compiler.
What is a CLR?
Full form of CLR is Common Language Runtime and it forms the heart of the .NET framework.All Languages have runtime and it is the responsibility of the runtime to take care of the code execution of the program. For example, VC++ has MSCRT40.DLL, VB6 has MSVBVM60.DLL,and Java has Java Virtual Machine etc. Similarly, .NET has CLR. Following are the responsibilities of CLR
Garbage Collection:-CLR automatically manages memory thus eliminating memory leaks. When objects are not referred, GC automatically releases those memories thus providing efficient memory management.
Code Access Security:-CAS grants rights to program depending on the security configuration of the machine. Example the program has rights to edit or create a new file but the security configuration of machine does not allow the program to delete a file. CAS will take care that the code runs under the environment of machines security configuration.
Code Verification:-This ensures proper code execution and type safety while the code runs. It prevents the source code to perform illegal operation such as accessing invalid memory locations etc.
IL (Intermediate language)-to-native translators and optimizer’s:-CLR uses JIT, compiles the IL code to machine code, and then executes. CLR also determines depending on platform what is optimized way of running the IL code.
What is CTS?
In order that two language communicate smoothly CLR has CTS (Common Type System).Example in VB you have Integer and in C++ you have long these datatypes are not compatible so the interfacing between them is very complicated. In order that these two different languages communicate Microsoft introduced Common Type System. So Integer data type in VB6 and int data type in C++ will convert it to System.int32, which is data type of CTS. CLS,which is covered in the coming question, is subset of CTS.
Note: If you have undergone COM programming period interfacing VB6 application with VC++ application was a real pain as the datatype of both languages did not have a common ground where they can come and interface, by having CTS interfacing is smooth.
What is a CLS (Common Language Specification)?
This is a subset of the CTS, which all .NET languages are expected to support. It was always a dream of Microsoft to unite all different languages in to one umbrella and CLS is one-step towards that. Microsoft has defined CLS, which are nothing but guidelines, that language should follow so that it can communicate with other .NET languages in a seamless manner.
What is a Managed Code?
Managed code runs inside the environment of CLR i.e. .NET runtime. In short, all IL are managed code. However, if you are using some third party software example VB6 or VC++ component they are unmanaged code, as .NET runtime (CLR) does not have control over the source code execution of these languages.
What is a Assembly?
Assembly is unit of deployment like EXE or a DLL.
1 An assembly consists of one or more files (dlls, exe’s, html files etc.), and represents a group of resources, type definitions, and implementations of those types. An assembly may also contain references to other assemblies. These resources, types and references are described in a block of data called a manifest. The manifest is part of the assembly, thus making the assembly self-describing.
2 An assembly is completely self-describing. An assembly contains metadata information, which is used by the CLR for everything from type checking an security to actually invoking the components methods. As all information is in the assembly itself, it is independent of registry. This is the basic advantage as compared to COM where the version was stored in registry.
3 Multiple versions can be deployed side by side in different folders. These different versions can execute at the same time without interfering with each other. Assemblies can be private or shared. For private assembly deployment, the assembly is copied to the same directory as the client program that references it. No registration is needed, and no fancy installation program is required. When the component is removed, no registry cleanup is needed, and no uninstall program is required. Just delete it from the hard drive.
4In shared assembly deployment, an assembly is installed in the Global Assembly Cache (or GAC). The GAC contains shared assemblies that are globally accessible to all .NET applications on the machine.
What are the different types of Assembly?
There are two types of assembly Private and Public assembly. A private assembly is normally used by a single application, and is stored in the application's directory, or a sub-directory beneath. A shared assembly is normally stored in the global assembly cache, which is a repository of assemblies maintained by the .NET runtime. Shared assemblies are usually libraries of code, which many applications will find useful, e.g. Crystal report classes that will be used by all application for Reports.
What is NameSpace?
Namespace has two basic functionality:-
1NameSpace Logically group types, example System.Web.UI logically groups UI related features.
2In Object Oriented world, many times it is possible that programmers will use the same class name. Qualifying NameSpace with class name can avoid this collision.
What is Difference between NameSpace and Assembly?
Following are the differences between namespace and assembly:
1 Assembly is physical grouping of logical units, Namespace, logically groups classes.
2 Namespace can span multiple assembly.
If you want to view an Assembly how do you go about it? or What is ILDASM?
When it comes to understanding of internals, nothing can beat ILDASM. ILDASM converts the whole ‘exe’ or ‘dll’ in to IL code. To run ILDASM you have to go to ‘C:\Program Files\Microsoft Visual Studio .NET 2003\SDK\v1.1\Bin’. Note that we had v1.1 you have to probably change it depending on the type of framework version you have.
If you run IDASM.EXE from the path you will be popped with the IDASM exe program as shown in figure ILDASM. Click on file and browse to the respective directory for the DLL whose assembly you want to view. After you select the DLL you will be popped with a tree view details of the DLL as shown in figure ILDASM. On double clicking on manifest, you will be able to view details of assembly, internal IL code etc as shown in Figure ‘Manifest View’.
Note: The version number are in the manifest itself which is defined with the DLL or EXE thus making deployment much easier as compared to COM where the information was stored in registry. Note the version information in Figure Manifest view.
What is Manifest?
Assembly metadata is stored in Manifest. Manifest contains all the metadata needed to do the following things (See Figure Manifest View for more details):
1Version of assembly.
2 Security identity.
3Scope of the assembly.
4Resolve references to resources and classes.
The assembly manifest can be stored in a PE file either (an .exe or) .dll with Microsoft intermediate language (MSIL code with Microsoft intermediate language (MSIL) code or in a stand-alone PE file, that contains only assembly manifest information.
Where is version information stored of an assembly?
Version information is stored in assembly inside the manifest.
Is versioning applicable to private assemblies?
Versioning concept is only applicable to global assembly cache (GAC) as private assembly lie in their individual folders. This does not mean versioning is not needed , you can still version it to have better version control on the project.
What is GAC? or In what situations will you register .NET assembly in GAC?
GAC (Global Assembly Cache) is where all shared .NET assembly reside. GAC is used in the following situations:-
1 If the application has to be shared among several application.
2 If the assembly has some special security, requirements like only administrators can remove the assembly. If the assembly is private
Registering .NET assembly in GAC can lead to the old problem of DLL hell, where COM version was stored in central registry. So GAC should be used when absolutely necessary.
what is the concept of strong names? or How do we generate strong names?
Or
What is use the of SN.EXE? or How do we apply strong names to assembly?
Or
How do you sign an assembly?
Strong name is similar to GUID (It is supposed to be unique in space and time) in COM components. Strong Name is only needed when we need to deploy assembly in GAC. Strong Names helps GAC to differentiate between two versions. Strong names use public key cryptography (PKC) to ensure that no one can spoof it.PKC use public key and private key concept.
Following are the step to generate a strong name and sign a assembly:-
Step1Go to "Visual Studio Command Prompt". See the below figure "Visual studio Command prompt". Note the samples are compiled in 2005 but 2003 users do not have to worry about it. Same type of command prompt will be seen in 2003 also.
*After generation of the file you can view the SNK file in a simple notepad
*After the SNK file is generated its time to sign the project with this SNK file.
Click on project & then click on "classlibrary1 properties" menu to sign the assembly
Click on project -- properties and the browse the SNK file from the respective folder
and compile the project.
Click on ‘Use a key file’ to sign the assembly with strong name
How to add and remove an assembly from GAC?
There are two ways to install .NET assembly in GAC:-
*Using Microsoft Installer Package. You can get download of installer from http://www.microsoft.com. (
Click here to view)
*Using Gacutil. Go to "Visual Studio Command Prompt" and type "gacutil -i(assembly name)", where (assembly name) is the DLL name of the project.
What is Delay signing?
During development process you will need strong name keys to be exposed to developer which is not a good practice from security aspect point of view.In such situations you can assign the key later on and during development you an use delay signing
Following is process to delay sign an assembly:
*First obtain your string name keys using SN.EXE.
*Annotate the source code for the assembly with two custom attributes from
System.Reflection: AssemblyKeyFileAttribute, which passes the name of the file containing the public key as a parameter to its constructor.
AssemblyDelaySignAttribute, which indicates that delay signing, is being used by passing true as a parameter to its constructor. For example as shown below:
[Visual Basic]
<Assembly: AssemblyKeyFileAttribute ("myKey.snk")>
<Assembly: AssemblyDelaySignAttribute (true)>
[C#]
[Assembly: AssemblyKeyFileAttribute ("myKey.snk")]
[Assembly: AssemblyDelaySignAttribute (true)]
The compiler inserts the public key into the assembly manifest and reserves space in the PE file for the full strong name signature. The real public key must be stored while the assembly is built so that other assemblies that reference this assembly can obtain the key to store in their own assembly reference.
*Because the assembly does not have a valid strong name signature, the verification of that signature must be turned off. You can do this by using the –Vr option with the
Strong Name tool. The following example turns off verification for an assembly called
myAssembly.dll.
Sn -Vr myAssembly.dll Just before shipping, you submit the assembly to your organization signing authority for the actual strong name signing using the –R option with the Strong Name tool. The following example signs an assembly called myAssembly.dll with a strong name using the sgKey.snk key pair.
Sn -R myAssembly.dll sgKey.snk