Common Language Infrastructure

The Common Language Infrastructure (CLI) is an open specification (technical standard) developed by Microsoft and standardized by ISO[1] and ECMA[2] that describes executable code and a runtime environment that allows multiple high-level languages to be used on different computer platforms without being rewritten for specific architectures. This implies it is platform agnostic. The .NET Framework, .NET Core, Mono, DotGNU and Portable.NET are implementations of the CLI.

Overview

Overview of the Common Language Infrastructure
Visual overview of the Common Language Infrastructure (CLI)

Among other things, the CLI specification describes the following four aspects:

The Common Type System (CTS)
A set of data types and operations that are shared by all CTS-compliant programming languages.
The Metadata
Information about program structure is language-agnostic, so that it can be referenced between languages and tools, making it easy to work with code written in a language the developer is not using.
The Common Language Specification (CLS)
A set of base rules to which any language targeting the CLI should conform in order to interoperate with other CLS-compliant languages. The CLS rules define a subset of the Common Type System.
The Virtual Execution System (VES)
The VES loads and executes CLI-compatible programs, using the metadata to combine separately generated pieces of code at runtime.

All compatible languages compile to Common Intermediate Language (CIL), which is an intermediate language that is abstracted from the platform hardware. When the code is executed, the platform-specific VES will compile the CIL to the machine language according to the specific hardware and operating system.

Standardization and licensing

In August 2000, Microsoft, Hewlett-Packard, Intel, and others worked to standardize CLI. By December 2001, it was ratified by the ECMA, with ISO standardization following in April 2003.

Microsoft and its partners hold patents for CLI. ECMA and ISO require that all patents essential to implementation be made available under "reasonable and non-discriminatory (RAND) terms." It is common for RAND licensing to require some royalty payment, which could be a cause for concern with Mono. As of January 2013, neither Microsoft nor its partners have identified any patents essential to CLI implementations subject to RAND terms.

As of July 2009,[3] Microsoft added C# and CLI to the list of specifications that the Microsoft Community Promise applies to,[4] so anyone can safely implement specified editions of the standards without fearing a patent lawsuit from Microsoft. To implement the CLI standard requires conformance to one of the supported and defined profiles of the standard, the minimum of which is the kernel profile. The kernel profile is actually a very small set of types to support in comparison to the well known core library of default .NET installations. However, the conformance clause of the CLI allows for extending the supported profile by adding new methods and types to classes, as well as deriving from new namespaces. But it does not allow for adding new members to interfaces. This means that the features of the CLI can be used and extended, as long as the conforming profile implementation does not change the behavior of a program intended to run on that profile, while allowing for unspecified behavior from programs written specifically for that implementation.

In 2012, ECMA and ISO published the new edition of the CLI standard,[1][2] which is not covered by the Community Promise.[4]

Implementations

See also

Notes

  1. ^ a b ISO/IEC 23271:2012 - Information technology -- Common Language Infrastructure (CLI)
  2. ^ a b Standard ECMA-335 - 6th edition (June 2012)
  3. ^ "The ECMA C# and CLI Standards - Port 25: The Open Source Community at Microsoft". 2009-07-06.
  4. ^ a b Covered Specifications | Microsoft Open Specifications

References

.NET Framework

.NET Framework (pronounced as "dot net") is a software framework developed by Microsoft that runs primarily on Microsoft Windows. It includes a large class library named Framework Class Library (FCL) and provides language interoperability (each language can use code written in other languages) across several programming languages. Programs written for .NET Framework execute in a software environment (in contrast to a hardware environment) named Common Language Runtime (CLR), an application virtual machine that provides services such as security, memory management, and exception handling. As such, computer code written using .NET Framework is called "managed code". FCL and CLR together constitute the .NET Framework.

FCL provides user interface, data access, database connectivity, cryptography, web application development, numeric algorithms, and network communications. Programmers produce software by combining their source code with .NET Framework and other libraries. The framework is intended to be used by most new applications created for the Windows platform. Microsoft also produces an integrated development environment largely for .NET software called Visual Studio.

.NET Framework began as proprietary software, although the firm worked to standardize the software stack almost immediately, even before its first release. Despite the standardization efforts, developers, mainly those in the free and open-source software communities, expressed their unease with the selected terms and the prospects of any free and open-source implementation, especially regarding software patents. Since then, Microsoft has changed .NET development to more closely follow a contemporary model of a community-developed software project, including issuing an update to its patent promising to address the concerns.

.NET Framework led to a family of .NET platforms targeting mobile computing, embedded devices, alternative operating systems, and web browser plug-ins. A reduced version of the framework, .NET Compact Framework, is available on Windows CE platforms, including Windows Mobile devices such as smartphones. .NET Micro Framework is targeted at very resource-constrained embedded devices. Silverlight was available as a web browser plugin. Mono is available for many operating systems and is customized into popular smartphone operating systems (Android and iOS) and game engines. .NET Core targets the Universal Windows Platform (UWP), and cross-platform and cloud computing workloads.

Application domain

An application domain is a mechanism (similar to a process in an operating system) used within the Common Language Infrastructure (CLI) to isolate executed software applications from one another so that they do not affect each other. Each application domain has its own virtual address space which scopes the resources for the application domain using that address space.

Assembly (CLI)

Defined by Microsoft for use in recent versions of Windows, an assembly in the Common Language Infrastructure (CLI) is a compiled code library used for deployment, versioning, and security. There are two types: process assemblies (EXE) and library assemblies (DLL). A process assembly represents a process that will use classes defined in library assemblies. CLI assemblies contain code in CIL, which is usually generated from a CLI language, and then compiled into machine language at run time by the just-in-time compiler. In the .NET Framework implementation, this compiler is part of the Common Language Runtime (CLR).

An assembly can consist of one or more files. Code files are called modules. An assembly can contain more than one code module. And since it is possible to use different languages to create code modules, it is technically possible to use several different languages to create an assembly. Visual Studio however does not support using different languages in one assembly.

C Sharp (programming language)

C# (pronounced C sharp) is a general-purpose, multi-paradigm programming language encompassing strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines. It was developed around 2000 by Microsoft within its .NET initiative and later approved as a standard by Ecma (ECMA-334) and ISO (ISO/IEC 23270:2018). C# is one of the programming languages designed for the Common Language Infrastructure.

C# was designed by Anders Hejlsberg, and its development team is currently led by Mads Torgersen. The most recent version is C# 7.3, which was released in 2018 alongside Visual Studio 2017 version 15.7.2.

Code Access Security

Code Access Security (CAS), in the Microsoft .NET framework, is Microsoft's solution to prevent untrusted code from performing privileged actions. When the CLR loads an assembly it will obtain evidence for the assembly and use this to identify the code group that the assembly belongs to. A code group contains a permission set (one or more permissions). Code that performs a privileged action will perform a code access demand which will cause the CLR to walk up the call stack and examine the permission set granted to the assembly of each method in the call stack.

The code groups and permission sets are determined by the administrator of the machine who defines the security policy.

Common Intermediate Language

Common Intermediate Language (CIL), formerly called Microsoft Intermediate Language (MSIL), is the lowest-level human-readable programming language defined by the Common Language Infrastructure (CLI) specification and is used by the .NET Framework, .NET Core, and Mono. Languages which target a CLI-compatible runtime environment compile to CIL, which is assembled into an object code that has a bytecode-style format. CIL is an object-oriented assembly language, and is entirely stack-based. Its bytecode is translated into native code or—most commonly—executed by a virtual machine.

CIL was originally known as Microsoft Intermediate Language (MSIL) during the beta releases of the .NET languages. Due to standardization of C# and the Common Language Infrastructure, the bytecode is now officially known as CIL.

Common Language Runtime

The Common Language Runtime (CLR), the virtual machine component of Microsoft's .NET framework, manages the execution of .NET programs. Just-in-time compilation converts the managed code (compiled intermediate language code), into machine instructions which are then executed on the CPU of the computer. The CLR provides additional services including memory management, type safety, exception handling, garbage collection, security and thread management. All programs written for the .NET framework, regardless of programming language, are executed by the CLR. All versions of the .NET framework include CLR. The CLR team was started June 13, 1998.

CLR implements the Virtual Execution System (VES) as defined in the Common Language Infrastructure (CLI) standard, initially developed by Microsoft itself. A public standard defines the Common Language Infrastructure specification.

Common Type System

In Microsoft's .NET Framework, the Common Type System (CTS) is a standard that specifies how type definitions and specific values of types are represented in

computer memory. It is intended to allow programs written in different programming languages to easily share information. As used in programming languages, a type can be described as a definition of a set of values (for example, "all integers between 0 and 10"), and the allowable operations on those values (for example, addition and subtraction).

The specification for the CTS is contained in Ecma standard 335, "Common Language Infrastructure (CLI) Partitions I to VI." The CLI and the CTS were created by Microsoft, and the Microsoft .NET framework is an implementation of the standard.

Delegate (CLI)

A delegate is a form of type-safe function pointer used by the Common Language Infrastructure (CLI). Delegates specify a method to call and optionally an object to call the method on. Delegates are used, among other things, to implement callbacks and event listeners. A delegate object encapsulates a reference to a method. The delegate object can then be passed to code that can call the referenced method, without having to know at compile time which method will be invoked.

A multicast delegate is a delegate that points to several methods. Multicast delegation is a mechanism that provides functionality to execute more than one method. There is a list of delegates maintained internally, and when the multicast delegate is invoked, the list of delegates is executed.

In C#, delegates are often used to implement callbacks in event driven programming. For example, a delegate may be used to indicate which method should be called when the user clicks on some button. Delegates allow the programmer to notify several methods that an event has occurred.

Framework Class Library

The Framework Class Library (FCL) is a standard library and Microsoft's .NET Framework implementation of the Standard Libraries as defined in the Common Language Infrastructure. The FCL is a collection of reusable classes, interfaces and value types. The Base Class Library (BCL) is the core of the FCL and provides the most fundamental functionality, which includes classes in namespaces System, System.CodeDom, System.Collections, System.Diagnostics, System.Globalization, System.IO, System.Resources and System.Text.

Global Assembly Cache

The Global Assembly Cache (GAC) is a machine-wide CLI assembly cache for the Common Language Infrastructure (CLI) in Microsoft's .NET Framework. The approach of having a specially controlled central repository addresses the flaws in the shared library concept and helps to avoid pitfalls of other solutions that led to drawbacks like DLL hell.

List of CLI languages

CLI languages are computer programming languages that are used to produce libraries and programs that conform to the Common Language Infrastructure (CLI) specifications. With some notable exceptions, most CLI languages compile entirely to the Common Intermediate Language (CIL), an intermediate language that can be executed using an implementation of CLI such as the Common Language Runtime (CLR, a part of the Microsoft .NET Framework and .NET Core), Mono, or Portable.NET. Some of these languages also require the Dynamic Language Runtime (DLR).

As the program is being executed, the CIL code is just-in-time compiled (and cached) to the machine code appropriate for the architecture on which the program is running. This step can be omitted manually by caching at an earlier stage using an "ahead of time" compiler such as Microsoft's ngen.exe and Mono's "-aot" option.

Manifest (CLI)

In the .Net Framework, an assembly manifest is a text file containing metadata about CLI assemblies. It describes the relationship and dependencies of the components in the assembly, versioning information, scope information and the security permissions required by the assembly.

The manifest information embedded within an assembly can be viewed using IL Disassembler (ILDASM.exe) which is available as part of Microsoft Windows SDK.

Metadata (CLI)

Metadata, in the Common Language Infrastructure (CLI), refers to certain data structures embedded within the Common Intermediate Language (CIL) code that describes the high-level structure of the code. Metadata describes all classes and class members that are defined in the assembly, and the classes and class members that the current assembly will call from another assembly. The metadata for a method contains the complete description of the method, including the class (and the assembly that contains the class), the return type and all of the method parameters.

A CLI language compiler will generate the metadata and store this in the assembly containing the CIL. When the run-time executes CIL it will check to make sure that the metadata of the called method is the same as the metadata that is stored in the calling method. This ensures that a method can only be called with exactly the right number of parameters and exactly the right parameter types.

The Windows Runtime application platform, present in Windows 8 and Windows Phone 8, makes use of the CLI metadata format to describe component interfaces for code written in any of the supported programming languages. A difference in use within the Common Language Runtime is that an assembly typically does not contain any CIL instructions.

Native Image Generator

The Native Image Generator, or simply NGen, is the ahead-of-time compilation (AOT) service of the .NET Framework. It allows a CLI assembly to be pre-compiled instead of letting the Common Language Runtime (CLR) do a just-in-time compilation (JIT) at runtime. In some cases the execution will be significantly faster than with JIT.

Platform Invocation Services

Platform Invocation Services, commonly referred to as P/Invoke, is a feature of Common Language Infrastructure implementations, like Microsoft's Common Language Runtime, that enables managed code to call native code.

Managed code, such as C# or VB.NET, provides native access to classes, methods, and types defined within the libraries that make up the .NET framework. While the .NET framework provides an extensive set of functionality, it may lack access to many lower level operating system libraries normally written in unmanaged code or third party libraries also written in unmanaged code. P/Invoke is the technique a programmer can use to access functions in these libraries. Calls to functions within these libraries occur by declaring the signature of the unmanaged function within managed code, which serves as the actual function that can be called like any other managed method. The declaration references the library's file path and defines the function parameters and return in managed types that are most likely to be implicitly marshaled to and from the unmanaged types by the common language run-time (CLR). When the unmanaged data types become too complex for a simple implicit conversion from and to managed types, the framework allows the user to define attributes on the function, return, and/or the parameters to explicitly refine how the data should be marshaled so as not to lead to exceptions in trying to do so implicitly. There are many abstractions of lower level programming concepts available to managed code programmers as compared to programming in unmanaged languages. As a result, a programmer with only managed code experience will need to brush up on programming concepts such as pointers, structures, and passing by reference to overcome some of the more basic, but common obstacles in using P/Invoke.

Shared Source Common Language Infrastructure

The Shared Source Common Language Infrastructure (SSCLI), previously codenamed Rotor, is Microsoft's shared source implementation of the CLI, the core of .NET. Although the SSCLI is not suitable for commercial use due to its license, it does make it possible for programmers to examine the implementation details of many .NET libraries and to create modified CLI versions. Microsoft provides the Shared Source CLI as a reference CLI implementation suitable for educational use.

Standard Libraries (CLI)

The Common Language Infrastructure (CLI) includes the Standard Libraries in order to encapsulate a large number of common functions, such as file reading and writing, XML document manipulation, exception handling, application globalization, network communication, threading and reflection, which makes the programmer's job easier. It is much larger in scope than standard libraries for most other languages, including C++, and is comparable in scope and coverage to the standard libraries of Java. The Framework Class Library (FCL) is the origin of the Standard Libraries as the .NET Framework, which includes the FCL, is the first implementation of the CLI.

Virtual Execution System

The Virtual Execution System (VES) is a run-time system of the Common Language Infrastructure CLI which provides an environment for executing managed code. It provides direct support for a set of built-in data types, defines a hypothetical machine with an associated machine model and state, a set of control flow constructs, and an exception handling model. To a large extent, the purpose of the VES is to provide the support required to execute the Common Intermediate Language CIL instruction set.

Common Language Infrastructure
Architecture
Components
Standard
Libraries
Implementations
Languages
Organizations
Standards of Ecma International
Application interfaces
File systems (tape)
File systems (disk)
Graphics
Programming languages
Radio link interfaces
Other
ISO standards by standard number
1–9999
10000–19999
20000+

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