BASICS OF .NET FRAMEWORK

.NET FRAMEWORK
The .Net Framework is a key Microsoft offering and it provides a Multilanguage environment that enables you to develop , deploy, and run Windows applications, Web applications as well as Web services.
The .Net languages extends developers capabilities by introducing Structured Exception Handling, Multi Threaded Programming, Versioning, ability to quickly create and use Web Services etc. The following link gives you an overview of each important

components in the .Net Framework .

The Microsoft .Net Framework is a platform that provides tools and technologies you need to build Networked Applications as well as Distributed Web Services and Web Applications. The .Net Framework provides the necessary compile time and run-time foundation to build and run any language that conforms to the Common Language Specification (CLS).The main two components of .Net Framework are Common Language Runtime (CLR) and .Net Framework Class Library (FCL).


The Common Language Runtime (CLR) is the runtime environment of the .Net Framework , that executes and manages all running code like a Virtual Machine. The .Net Framework Class Library (FCL) is a huge collection of language-independent and type-safe reusable classes. The .Net Framework Class Libraries (FCL) are arranged into a logical grouping according to their functionality and usability is called Namespaces. In the following sections describes how to .Net Framework manages the code in compile time and run time .


CLR


The Common Language Runtime (CLR) is an Execution Environment . It works as a layer between Operating Systems and the applications written in .Net languages that conforms to the Common Language Specification (CLS). The main function of Common Language Runtime (CLR) is to convert the Managed Code into native code and then execute the Program. The Managed Code compiled only when it needed, that is it converts the appropriate instructions when each function is called . The Common Language Runtime (CLR) 's Just In Time (JIT) compilation converts Intermediate Language (MSIL) to native code on demand at application run time.
During the execution of the program ,the Common Language Runtime (CLR) manages memory, Thread execution, Garbage Collection (GC) , Exception Handling, Common Type System (CTS), code safety verifications, and other system services. The CLR ( Common Language Runtime ) defines the Common Type System (CTS), which is a standard type system used by all .Net languages . That means all .NET programming languages uses the same representation for common Data Types , so Common Language Runtime (CLR) is a language-independent runtime environment . The Common Language Runtime (CLR) environment is also referred to as a managed environment, because during the execution of a program it also controls the interaction with the Operating System. In the coming section you can see what are the main functions of Common Language Runtime (CLR).






FCL
The .Net Framework class library (FCL) provides the core functionality of .Net Framework architecture . The .Net Framework Class Library (FCL) includes a huge collection of reusable classes , interfaces, and value types that expedite and optimize the development process and provide access to system functionality.
The .Net Framework class library (FCL) organized in a hierarchical tree structure and it is divided into Namespaces. Namespaces is a logical grouping of types for the purpose of identification. Framework class library (FCL) provides the consistent base types that are used across all .NET enabled languages. The Classes are accessed by namespaces, which reside within Assemblies. The System Namespace is the root for types in the .NET Framework. The .Net Framework class library (FCL) classes are managed classes that provide access to System Services . The .Net Framework class library (FCL) classes are object oriented and easy to use in program developments. Moreover, third-party components can integrate with the classes in the .NET Framework.



CLS
Common Language Specification (CLS) is a set of basic language features that .Net Languages needed to develop Applications and Services , which are compatible with the .Net Framework. When there is a situation to communicate Objects written in different .Net Complaint languages , those objects must expose the features that are common to all the languages . Common Language Specification (CLS) ensures complete interoperability among applications, regardless of the language used to create the application.
Common Language Specification (CLS) defines a subset of Common Type System (CTS) . Common Type System (CTS) describes a set of types that can use different .Net languages have in common , which ensure that objects written in different languages can interact with each other. Most of the members defined by types in the .NET Framework Class Library (FCL) are Common Language Specification (CLS) compliant Types. Moreover Common Language Specification (CLS) standardized by ECMA .


CTS
Common Type System (CTS) describes a set of types that can be used in different .Net languages in common . That is , the Common Type System (CTS) ensure that objects written in different .Net languages can interact with each other. For Communicating between programs written in any .NET complaint language, the types have to be compatible on the basic level .
These types can be Value Types or Reference Types . The Value Types are passed by values and stored in the stack. The Reference Types are passed by references and stored in the heap. Common Type System (CTS) provides base set of Data Types which is responsible for cross language integration. The Common Language Runtime (CLR) can load and execute the source code written in any .Net language, only if the type is described in the Common Type System (CTS) .Most of the members defined by types in the .NET Framework Class Library (FCL) are Common Language Specification (CLS) compliant Types.

MSIL
MSIL stands for Microsoft Intermediate Language. We can call it as Intermediate Language (IL) or Common Intermediate Language (CIL). During the compile time , the compiler convert the source code into Microsoft Intermediate Language (MSIL) .Microsoft Intermediate Language (MSIL) is a CPU-independent set of instructions that can be efficiently converted to the native code. During the runtime the Common Language Runtime (CLR)'s Just In Time (JIT) compiler converts the Microsoft Intermediate Language (MSIL) code into native code to the Operating System.
When a compiler produces Microsoft Intermediate Language (MSIL), it also produces Metadata. The Microsoft Intermediate Language (MSIL) and Metadata are contained in a portable executable (PE) file . Microsoft Intermediate Language (MSIL) includes instructions for loading, storing, initializing, and calling methods on objects, as well as instructions for arithmetic and logical operations, control flow, direct memory access, exception handling, and other operations

PE (PORTABLE EXECUTABLE FILE)
The Portable Executable (PE) format is a file format for executables, object code, and DLLs, used in 32-bit and 64-bit versions of Windows operating systems.
The PE file format was defined to provide the best way for the Windows Operating System to execute code and also to store the essential data which is needed to run a program. Portable Executable File Format is derived from the Microsoft Common Object File Format (COFF).
JIT (JUST IN TIME )COMPILER
The .Net languages , which is conforms to the Common Language Specification (CLS), uses its corresponding runtime to run the application on different Operating Systems . During the code execution time, the Managed Code compiled only when it is needed, that is it converts the appropriate instructions to the native code for execution just before when each function is called. This process is called Just In Time (JIT) compilation, also known as Dynamic Translation . With the help of Just In Time Compiler (JIT) the Common Language Runtime (CLR) doing these tasks.
The Common Language Runtime (CLR) provides various Just In Time compilers (JIT) and each works on a different architecture depending on Operating System. That is why the same Microsoft Intermediate Language (MSIL) can be executed on different Operating Systems without rewrite the source code. Just In Time (JIT) compilation preserves memory and save time during application initialization. Just In Time (JIT) compilation is used to run at high speed, after an initial phase of slow interpretation. Just In Time Compiler (JIT) code generally offers far better performance than interpreters.


MANAGED CODE IN .NET FRAMEWORK


Managed Code in Microsoft .Net Framework, is the code that has executed by the Common Language Runtime (CLR) environment. On the other hand Unmanaged Code is directly executed by the computer's CPU. Data types, error-handling mechanisms, creation and destruction rules, and design guidelines vary between managed and unmanaged object models.
The benefits of Managed Code include programmers convenience and enhanced security . Managed code is designed to be more reliable and robust than unmanaged code , examples are Garbage Collection , Type Safety etc. The Managed Code running in a Common Language Runtime (CLR) cannot be accessed outside the runtime environment as well as cannot call directly from outside the runtime environment. This makes the programs more isolated and at the same time computers are more secure . Unmanaged Code can bypass the .NET Framework and make direct calls to the Operating System. Calling unmanaged code presents a major security risk.


METADATA


Metadata in .Net is binary information which describes the characteristics of a resource . This information include Description of the Assembly , Data Types and members with their declarations and implementations, references to other types and members , Security permissions etc. A module's metadata contains everything that needed to interact with another module.
During the compile time Metadata created with Microsoft Intermediate Language (MSIL) and stored in a file called a Manifest . Both Metadata and Microsoft Intermediate Language (MSIL) together wrapped in a Portable Executable (PE) file. During the runtime of a program Just In Time (JIT) compiler of the Common Language Runtime (CLR) uses the Metadata and converts Microsoft Intermediate Language (MSIL) into native code. When code is executed, the runtime loads metadata into memory and references it to discover information about your code's classes, members, inheritance, and so on. Moreover Metadata eliminating the need for Interface Definition Language (IDL) files, header files, or any external method of component reference.



ASSEMBLY

Microsoft .Net Assembly is a logical unit of code, it contains code that the Common Language Runtime (CLR) executes. Assembly is really a collection of types and resource information that are built to work together and form a logical unit of functionality. During the compile time Metadata is created, with Microsoft Intermediate Language (MSIL), and stored in a file called a Manifest . Both Metadata and Microsoft Intermediate Language (MSIL) together wrapped in a Portable Executable (PE) file. Manifest contains information about itself. This information is called Assembly Manifest, it contains information about the members, types, references and all the other data that the runtime needs for execution.
Every Assembly you create contains one or more program files and a Manifest. There are two types program files : Process Assemblies (EXE) and Library Assemblies (DLL). Each Assembly can have only one entry point (that is, DllMain, WinMain, or Main). We can create two types of Assembly, private Assembly and shared Assembly . A private Assembly is used only by a single application, and usually it is stored in that application's install directory. A shared Assembly is one that can be referenced by more than one application. If multiple applications need to access an Assembly, we should add the Assembly to the Global Assembly Cache (GAC).

GAC(GLOBAL ACCESS CACHE)
Each computer on which the Common Language Runtime is installed has a machine-wide code cache called the 'Global Assembly Cache'. The Global Assembly Cache (GAC) enables you to share assemblies across numerous applications.
The GAC is automatically installed with the .NET runtime. The global assembly cache is located in 'Windows/WinNT' directory and inherits the directory's access control list that administrators have used to protect the folder.
The approach of having a specially controlled central repository addresses the shared library concept and helps to avoid pitfalls of other solutions that lead to drawbacks like DLL hell.
The Global Assembly Cache Tool (Gacutil.exe), that allows you to view and manipulate the contents of the Global Assembly Cache.

CONTENT OF AN ASSEMLY
A .NET assembly can consist of following elements:
a) Assembly Manifest - The Metadata that describes the assembly and its contents
b) Type Metadata - Defines all types, their properties and methods.
c) MSIL - Microsoft intermediate language
d) A set of Resources - All other resources like icons, images etc.
Only the assembly manifest is required, but either types or resources are needed to give the assembly in any meaningful functionality.



PRIVATE AND SHARED ASSEMBLY

A private assembly is an assembly that is available to particular application where they are kept, and a Shared Assembly is a public assembly that is shared by multiple applications. That means, a Private Assembly cannot be references outside the scope of the folder where they are kept and a Shared Assembly is one that can be referenced by more than one application.
In order to share an assembly, the assembly must be explicitly built for this purpose by giving it a cryptographically strong name . By contrast, a private assembly name need only be unique within the application that uses it.
The classes that ship with the .NET Framework are all built as shared assemblies.


NAMESPACES

Namespaces are the way to organize .NET Framework Class Library into a logical grouping according to their functionality, usability as well as category they should belong to, or we can say Namespaces are logical grouping of types for the purpose of identification.
The .NET Framework Class Library (FCL ) is a large collection of thousands of Classes. These Classes are organized in a hierarchical tree. The System Namespaces is the root for types in the .NET Framework. We can uniquely identify any Class in the .NET Framework Class Library (FCL ) by using the full Namespaces of the class .In .Net languages every program is created with a default Namespaces . Programmers can also create their own Namespaces in .Net languages.

GARBAGE COLLECTION

The .Net Framework provides a new mechanism for releasing unreferenced objects from the memory (that is we no longer needed that objects in the program) ,this process is called Garbage Collection (GC). When a program creates an Object, the Object takes up the memory. Later when the program has no more references to that Object, the Object's memory becomes unreachable, but it is not immediately freed. The Garbage Collection checks to see if there are any Objects in the heap that are no longer being used by the application. If such Objects exist, then the memory used by these Objects can be reclaimed. So these unreferenced Objects should be removed from memory , then the other new Objects you create can find a place in the Heap.
The reclaimed Objects have to be Finalized later. Finalization allows a resource to clean up after itself when it is being collected. This releasing of unreferenced Objects is happening automatically in .Net languages by the Garbage Collector (GC). The programming languages like C++, programmers are responsible for allocating memory for Objects they created in the application and reclaiming the memory when that Object is no longer needed for the program. In .Net languages there is a facility that we can call Garbage Collector (GC) explicitly in the program by calling System.GC.Collect.