.NET Framework


1.1.   .NET FRAMEWORK

The .NET Framework is a software framework developed by Microsoft that runs primarily on Microsoft Windows. Software framework is an abstraction in which software providing generic functionality can be selectively changed by the user code, thus providing application specific software. Software framework is a universal and reusable software platform which is used to develop applications, products and solutions. This software framework includes:
-          Support programs,
-          Compilers,
-          Code libraries,
-          Application programming interface (API) and
-          Tool sets that bring together different components that enables development of a project or a solution.
The .NET Framework consists of two key elements which are important for your software development that is Common Language Runtime or CLR and set of libraries called the .NET Framework class libraries. The CLR or Common Language Runtime is important because it executes your applications. The .NET Framework class libraries provide the functional support your code will need when executing with the CLR regardless of programming language used.
There are two fundamentally different kinds of C++ applications you can develop with Visual C++ 2010. You can write application in classic C++ programming language. This language is defined by the ISO/IEC (International Standards Organization/International Electro technical Commission) language standard. The other application you can develop using Visual C++ 2010 is called C++/CLI. These programs will be referred to as CLR programs, or C++/CLI programs.

1.1.1.                 Development history of .NET Framework



The .NET Framework Development

Computer Company Microsoft started working on development of the .NET Framework in late 1990s. Original name of .NET Framework was Next Generation Services (NGWS). By the end of 2000 the first beta version of .NET 1.0 were released.
Windows XP does not come with any version of the .NET Framework installed. The .NET Framework 3.0 was included with Windows Server 2008 and Windows Vista. The first version of Windows 7 also came with .NET Framework 3.5.
Today the .NET Framework family also includes two versions for mobile or embedded device use. A reduced version of the framework, the .NET Compact Framework, is available on the Windows CE platforms, including Windows Mobile devices such as smartphones. The .NET Micro Framework is targeted at severely resource - constrained devices.

1.1.2.                 Design features of .NET Framework

 Components of .NET Framework are:
-          Interoperability
-          Common Language Runtime engine
-          Language independence
-          Base Class Library
-          Simplified deployment and
-          Portability

1.1.2.1.                      Interoperability

Because computer systems commonly require interaction between newer and older applications, the .NET Framework provides means to access functionality implemented in newer and older programs that execute outside the .NET environment. Access to COM components is provided in the System.Runtime.InteropServices and System.EnterpriseServices namespaces of the framework; access to other functionality is achieved using the P/Invoke feature.

1.1.2.2.                      Common Language Runtime Engine

The Common Language Runtime (CLR) serves as the execution engine of the .NET Framework. All .NET programs execute under the supervision of the CLR, guaranteeing certain properties and behaviors in the areas of memory management, security, and exception handling.

1.1.2.3.                      Language independence

The .NET Framework introduces a Common Type System, or CTS. The CTS specification defines all possible datatypes and programming constructs supported by the CLR and how they may or may not interact with each other conforming to the Common Language Infrastructure (CLI) specification. Because of this feature, the .NET Framework supports the exchange of types and object instances between libraries and applications written using any conforming .NET language.

1.1.2.4.                      Base Class Library

The Base Class Library (BCL), part of the Framework Class Library (FCL), is a library of functionality available to all languages using the .NET Framework. The BCL provides classes that encapsulate a number of common functions, including file reading and writing, graphic rendering, database interaction, XML document manipulation, and so on. It consists of classes, interfaces of reusable types that integrates with CLR(Common Language Runtime).

1.1.2.5.                      Simplified deployment

The .NET Framework includes design features and tools which help manage the installation of computer software to ensure it does not interfere with previously installed software, and it conforms to security requirements.

1.1.2.6.                      Security

The design addresses some of the vulnerabilities, such as buffer overflows, which have been exploited by malicious software. Additionally, .NET provides a common security model for all applications.

1.1.2.7.                      Portability

While Microsoft has never implemented the full framework on any system except Microsoft Windows, it has engineered the framework to be platform-agnostic, and cross-platform implementations are available for other operating systems (see Silverlight and the Alternative implementations section below). Microsoft submitted the specifications for the Common Language Infrastructure (which includes the core class libraries, Common Type System, and the Common Intermediate Language), the C# language, and the C++/CLI language to both ECMA and the ISO, making them available as official standards. This makes it possible for third parties to create compatible implementations of the framework and its languages on other platforms.

1.1.3.                 Architecture



Visual overview of the Common Language Infrastructure (CLI)

1.1.3.1.                      Common Language Infrastructure (CLI)

The purpose of the Common Language Infrastructure (CLI) is to provide a language-neutral platform for application development and execution, including functions for Exception handling, Garbage Collection, security, and interoperability. By implementing the core aspects of the .NET Framework within the scope of the CL, this functionality will not be tied to a single language but will be available across the many languages supported by the framework. Microsoft's implementation of the CLI is called the Common Language Runtime, or CLR. The CIL code is housed in CLI assemblies. As mandated by the specification, assemblies are stored in the Portable Executable (PE) format, common on the Windows platform for all DLL and EXE files. The assembly consists of one or more files, one of which must contain the manifest, which has the metadata for the assembly. The complete name of an assembly (not to be confused with the filename on disk) contains its simple text name, version number, culture, and public key token. Assemblies are considered equivalent if they share the same complete name, excluding the revision of the version number. A private key can also be used by the creator of the assembly for strong naming. The public key token identifies which public key an assembly is signed with. Only the creator of the keypair (typically the .NET developer signing the assembly) can sign assemblies that have the same strong name as a previous version assembly, since he is in possession of the private key. Strong naming is required to add assemblies to the Global Assembly Cache

1.1.3.2.                      Security

.NET has its own security mechanism with 2 general features: Code Access Security (CAS), and validation and verification. Code Access Security is based on evidence that is associated with a specific assembly. Typically the evidence is the source of the assembly (whether it is installed on the local machine or has been downloaded from the intranet or Internet). Code Access Security uses evidence to determine the permissions granted to the code. Other code can demand that calling code is granted a specified permission. The demand causes the CLR to perform a call stack walk: every assembly of each method in the call stack is checked for the required permission; if any assembly is not granted the permission a security exception is thrown.

1.1.3.3.                      Class library

Namespaces in the BCL
System
System.Diagnostics
System.Globalization
System.Resources
System.Text
System.Runtime.Serialization
System.Data

The .NET Framework includes a set of standard class libraries. The class library is organized in a hierarchy of namespaces. Most of the built-in APIs are part of either System.* or Microsoft.* namespaces. These class libraries implement a large number of common functions, such as file reading and writing, graphic rendering, database interaction, and XML document manipulation, among others. The .NET class libraries are available to all CLI compliant languages. The .NET Framework class library is divided into two parts: the Base Class Library and the Framework Class Library
The Base Class Library (BCL) includes a small subset of the entire class library and is the core set of classes that serve as the basic API of the Common Language Runtime.[11] The classes in mscorlib.dll and some of the classes in System.dll and System.core.dll are considered to be a part of the BCL. The BCL classes are available in both .NET Framework as well as its alternative implementations including .NET Compact Framework, Microsoft Silverlight and Mono.
The Framework Class Library (FCL) is a superset of the BCL classes and refers to the entire class library that ships with .NET Framework. It includes an expanded set of libraries, including Windows Forms, ADO.NET, ASP.NET, Language Integrated Query, Windows Presentation Foundation, Windows Communication Foundation among others. The FCL is much larger in scope than standard libraries for languages like C++, and comparable in scope to the standard libraries of Java.

1.1.3.4.                      Memory management

The .NET Framework CLR frees the developer from the burden of managing memory (allocating and freeing up when done); it handles memory management itself by detecting when memory can be safely freed. Memory is allocated to instantiations of .NET types (objects) from the managed heap, a pool of memory managed by the CLR. As long as there exists a reference to an object, which might be either a direct reference to an object or via a graph of objects, the object is considered to be in use. When there is no reference to an object, and it cannot be reached or used, it becomes garbage, eligible for collection. NET Framework includes a garbage collector which runs periodically, on a separate thread from the application's thread, that enumerates all the unusable objects and reclaims the memory allocated to them.
The .NET Garbage Collector (GC) is a non-deterministic, compacting, mark-and-sweep garbage collector. The GC runs only when a certain amount of memory has been used or there is enough pressure for memory on the system. Since it is not guaranteed when the conditions to reclaim memory are reached, the GC runs are non-deterministic. Each .NET application has a set of roots, which are pointers to objects on the managed heap (managed objects). These include references to static objects and objects defined as local variables or method parameters currently in scope, as well as objects referred to by CPU registers. When the GC runs, it pauses the application, and for each object referred to in the root, it recursively enumerates all the objects reachable from the root objects and marks them as reachable. It uses CLI metadata and reflection to discover the objects encapsulated by an object, and then recursively walk them. It then enumerates all the objects on the heap (which were initially allocated contiguously) using reflection. All objects not marked as reachable are garbage. This is the mark phase. Since the memory held by garbage is not of any consequence, it is considered free space. However, this leaves chunks of free space between objects which were initially contiguous. The objects are then compacted together to make used memory contiguous again. Any reference to an object invalidated by moving the object is updated by the GC to reflect the new location. The application is resumed after the garbage collection is over.
The GC used by .NET Framework is actually generational. Objects are assigned a generation; newly created objects belong to Generation 0. The objects that survive a garbage collection are tagged as Generation 1, and the Generation 1 objects that survive another collection are Generation 2 objects. The .NET Framework uses up to Generation 2 objects. Higher generation objects are garbage collected less frequently than lower generation objects. This helps increase the efficiency of garbage collection, as older objects tend to have a longer lifetime than newer objects. Thus, by removing older (and thus more likely to survive a collection) objects from the scope of a collection run, fewer objects need to be checked and compacted.

1.1.4.                 Standardization and licensing

In August 2000, Microsoft, Hewlett-Packard, and Intel worked to standardize CLI and the C# programming language. By December 2001, both were ratified ECMA standards (ECMA 335 and ECMA 334). ISO followed in April 2003 - the current version of the ISO standards are ISO/IEC 23271:2012 and ISO/IEC 23270:2006.
While Microsoft and their partners hold patents[citation needed] for the CLI and C#, ECMA and ISO require that all patents essential to implementation be made available under "reasonable and non-discriminatory terms". In addition to meeting these terms, the companies have agreed to make the patents available royalty-free.[citation needed]
However, this does not apply for the part of the .NET Framework which is not covered by the ECMA/ISO standard, which includes Windows Forms, ADO.NET, and ASP.NET. Patents that Microsoft holds in these areas may deter non-Microsoft implementations of the full framework.
On 3 October 2007, Microsoft announced that much of the source code for the .NET Framework Base Class Library (including ASP.NET, ADO.NET, and Windows Presentation Foundation) was to have been made available with the final release of Visual Studio 2008 towards the end of 2007 under the shared source Microsoft Reference License.[1] The source code for other libraries including Windows Communication Foundation (WCF), Windows Workflow Foundation (WF), and Language Integrated Query (LINQ) were to be added in future releases. Being released under the non-open source Microsoft Reference License means this source code is made available for debugging purpose only, primarily to support integrated debugging of the BCL in Visual Studio.

1.1.5.                 Alternate implementations

The Microsoft .NET Framework is the predominant implementation of .NET technologies. Other implementations for parts of the framework exist. Although the runtime engine is described by an ECMA/ISO specification, other implementations of it may be encumbered by patent issues; ISO standards may include the disclaimer, "Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights." It is more difficult to develop alternatives to the base class library (BCL), which is not described by an open standard and may be subject to copyright restrictions. Additionally, parts of the BCL have Windows-specific functionality and behavior, so implementation on non-Windows platforms can be problematic.
Some alternative implementations of parts of the framework are listed here.
·         Microsoft's .NET Micro Framework is a .NET platform for extremely resource-constrained devices. It includes a small version of the .NET CLR and supports development in C# (though some developers were able to use VB.NET,[19] albeit with an amount of hacking, and with limited functionalities) and debugging (in an emulator or on hardware), both using Microsoft Visual Studio. It also features a subset of the .NET base class libraries (about 70 classes with about 420 methods), a GUI framework loosely based on Windows Presentation Foundation, and additional libraries specific to embedded applications.
·         Mono is an implementation of the CLI and the .NET Base Class Library (BCL), and provides additional functionality. It is dual-licensed under free software and proprietary software licenses. It includes support for ASP.NET, ADO.NET, and Windows Forms libraries for a wide range of architectures and operating systems. It also includes C# and VB.NET compilers.
·         Portable.NET (part of DotGNU) provides an implementation of the Common Language Infrastructure (CLI), portions of the .NET Base Class Library (BCL), and a C# compiler. It supports a variety of CPUs and operating systems.
·         Microsoft's Shared Source Common Language Infrastructure is a non-free implementation of the CLR component of the .NET Framework. However, the last version only runs on Microsoft Windows XP SP2, and was not updated since 2006, therefore it does not contain all features of version 2.0 of the .NET Framework.
·         CrossNet is an implementation of the CLI and portions of the .NET Base Class Library (BCL). It is free software using the open source MIT License.

1.1.6.                 Criticism

1.1.6.1.                      Performance

The garbage-collector, which is integrated into the environment, can introduce unanticipated delays of execution over which the developer has little direct control, and it can cause runtime memory size to be larger than expected. "In large applications, the number of objects that the garbage collector needs to deal with can become very large, which means it can take a very long time to visit and rearrange all of them."
The .NET Framework currently does not provide support for calling Streaming SIMD Extensions (SSE) via managed code. However, Mono has provided support for SIMD Extensions as of version 2.2 within the Mono.Simd namespace; Mono's lead developer Miguel de Icaza has expressed hope that this SIMD support will be adopted by the CLR ECMA standard. Streaming SIMD Extensions have been available in x86 CPUs since the introduction of the Pentium III. Some other architectures such as ARM and MIPS also have SIMD extensions. In case the CPU lacks support for those extensions, the instructions are simulated in software.

1.1.6.2.                      Security

Unobfuscated managed CIL bytecode can often be easier to reverse-engineer than native code. One concern is over possible loss of trade secrets and the bypassing of license control mechanisms. To mitigate this, Microsoft included the Dotfuscator Community Edition obfuscation tool within Visual Studio .NET since 2002. Third-party obfuscation solutions are also available from vendors such as vmware, V.i. Labs, Xenocode, Red Gate Software and others.
.NET Decompiler programs such as .NET Reflector enable developers with no reverse-engineering skills to view the source code behind unobfuscated .NET assemblies (DLL/EXE). In contrast, applications built with Visual C++ are much harder to reverse-engineer and source code is almost never produced successfully, even with decompiling programs such as IDA Pro.

1.1.6.3.                      Availability

While the standards that make up .NET are inherently cross-platform, Microsoft's full implementation of .NET is only supported on Windows.Newer versions of the framework (3.5 and up) are not pre-installed in versions of Windows below Windows 7 (although newer versions are available via Windows Update). For this reason, applications must lead users without the framework through a procedure to install it. Some developers have expressed concerns about the large size of the .NET Framework runtime installers for end-users. The size is around 54 MB for .NET 3.0, 197 MB for .NET 3.5, and 250 MB for .NET 3.5 SP1 (while using web installer the typical download for Windows XP is around 50 MB — for Windows Vista, 20 MB). The size issue is partially solved with .NET 4 installer (x86 + x64) being 54 MB and not embedding full runtime installation packages for previous versions. The .NET 3.5 SP1 full installation package includes the full runtime installation packages for .NET 2.0 SP2 as well as .NET 3.0 SP2 for multiple operating systems (Windows XP/Server 2003 and Windows Vista/Server 2008) and for multiple CPU architectures (x86, x86-64, and IA-64).
The first service pack for version 3.5 mitigates this concern by offering a lighter-weight client-only subset of the .NET Framework. Two significant limitations should be noted, though. Firstly, the client-only subset is only an option on an existing Windows XP SP2 system that currently has no other version of the .NET Framework installed. In all other scenarios, the client-only installer will install the full version of the .NET Framework 3.5 SP1. Secondly, the client-only framework does not have a 64-bit option. However, the 4 release of the .NET Framework Client Profile will be available on all operating systems and all architectures (excluding Itanium) supported by the full .NET Framework.
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