Mono (software)

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File:Mono project logo.svg
Developer(s) Community, with Novell leadership.
Initial release June 30, 2004
Stable release 2.6.1 / December 18, 2009; 131387321 ago
Operating system Cross-platform
Type Platform
License GPLv2, LGPLv2 and MIT, or dual license[1]

Mono is a free and open source project led by Novell (formerly by Ximian) to create an Ecma standard compliant, .NET-compatible set of tools, including among others a C# compiler and a Common Language Runtime. Mono can be run on Linux, BSD, UNIX, Mac OS X, Solaris and Windows operating systems.



Miguel de Icaza became interested in .NET technology as soon as the .NET documents were released in December 2000. After looking at the byte code interpreter, he realized that there were no specifications for the metadata. In February 2001 de Icaza asked for the missing information on the metadata file format in the .NET mailing lists and at the same time started to work on a C# compiler written in C#, as an exercise in C#.[citation needed] In April 2001, ECMA published the missing file format, and at GUADEC (April 6–8, 2001) de Icaza demonstrated the features of his compiler (which by then was able to parse itself).

Internally at Ximian there was much discussion about building tools to increase productivity: making it possible to create more applications in less time and therefore reduce time and cost of development. After a feasibility study, which clearly stated that it was possible to build the technology, Ximian reassigned staff from other projects and created the Mono team. Lacking the resources to build a full .NET replacement on their own, they formed the Mono open source project, which was announced on July 19, 2001 at the O'Reilly conference.

Almost three years later, on June 30, 2004 Mono 1.0 was released.[2]

The logo of Mono is a monkey's face, mono being Spanish for monkey. The name relates to the monkeys and apes that are a central theme within Ximian, such as the GNOME Project's logo (a monkey's footprint), the Bonobo project (bonobos are a species of chimpanzee), the Novell Evolution (formerly Ximian Evolution) Project, and the Ximian logo itself (a monkey's silhouette). According to the Mono FAQ, the origin of the name is "We like monkeys."[3]

Current status and roadmap

Mono's current version is 2.6 (as of December 2009). This version provides the core API of the .NET Framework as well as support for Visual Basic.NET and C# versions 2.0, 3.0 and 4.0. LINQ to objects and XML is part of the distribution, but not LINQ to SQL. C# 3.0 is now the default mode of operation for the C# compiler. Windows Forms 2.0 is also now supported. Support for C# 4.0 is feature complete (as of December 2009) but not yet released in a stable version.[4]

Implementation of .NET Framework 3.0 (i.e. WPF) is under development under an experimental Mono subproject called "Olive", but the availability of a Mono framework supporting .NET 3.0 is still not planned yet.[5][6]

The Mono project has also created a VB.NET compiler as well as a runtime designed for running VB.NET applications. It is currently being developed by Rolf Bjarne Kvinge.

An open source implementation of Silverlight, called Moonlight, is now underway and has been included since Mono 1.9.[7] Moonlight 1.0, which supports the Silverlight 1.0 APIs, was released January 20, 2009. A Moonlight 2.0 Beta release, which has pre-alpha support for Silverlight 2.0 (first version which is scriptable with .NET), was released on 17 August 2009.[8]

Mono components

Mono consists of three groups of components:

  1. Core components
  2. Mono/Linux/GNOME development stack
  3. Microsoft compatibility stack.

The core components include the C# grammars and semantics and the Common Language Infrastructure. These components are based on the Ecma-334 and Ecma-335 standards,[9] allowing Mono to provide a standards compliant, free and open source CLI virtual machine. Microsoft issued a statement that covers both standards under their Community Promise license.[10]

The Mono/Linux/GNOME development stack provide tools for application development while leveraging existing GNOME and Free and Open Source libraries. These include: Gtk# for GUI development, Mozilla libraries for working with the Gecko rendering engine, Unix integration libraries, database connectivity libraries, a security stack, and the XML schema language RelaxNG. Gtk# allows Mono applications to integrate into the Gnome desktop as native applications. The database libraries provide connectivity to MySQL, SQLite, PostgreSQL, Firebird, Open Database Connectivity (ODBC), Microsoft SQL Server (MSSQL), Oracle, the object-relational database db4o, and many others. The Mono project tracks developing database components at its website.[11]

The Microsoft compatibility stack provides a pathway for porting Windows .NET applications to Linux. This group of components include ADO.NET, ASP.NET, and Windows.Forms, among others. As these components are not covered by ECMA standards, some of them remain subject to patent fears and concerns.

Framework architecture

File:Mono architecture.svg
Simplified Mono architecture

Just-in-time engine

The Mono runtime contains a just-in-time compilation (JIT) engine for a number of processors: MIPS (in 32-bit mode only), x86, SPARC, PowerPC, ARM, S390 (in 32-bit and 64-bit mode), and x86-64 and IA64 for 64-bit modes. The runtime will perform a just-in-time compilation to the machine's native code which is cached as the application runs. It is also possible to precache the native image before execution. (For other supported systems not listed, an interpreter executes each bytecode instruction sequentially, without compiling the image to native code. JIT compilation outperforms interpretation under most circumstances.)

However, the current conservative garbage collector (the "Boehm-Demers-Wiser Conservative Garbage Collector")[12][13] presents a serious drawback compared to commercial garbage collected runtimes, like the Java Virtual Machine or the .NET framework's runtime. There is a theoretical chance of running into memory leaks that may even result in an abrupt end of an application's execution due to an out-of-memory condition. This is especially a grave concern for server applications meant to run for a long time. As of July 2009, development of a modern garbage collector called "Simple Generational GC" (SGen-GC) is under way, but a date for incorporation into a production release has not been set.[12]

Class library

The class library provides a comprehensive set of facilities for application development. They are primarily written in C#, but due to the Common Language Specification they can be used by any .NET language. The class library is structured into namespaces, and deployed in shared libraries known as assemblies. Speaking of the .NET framework is primarily referring to this class library.[14]

Namespaces and assemblies

Namespaces are a mechanism for logically grouping similar classes into a hierarchical structure. This prevents naming conflicts. The structure is implemented using dot-separated words, where the most common top-level namespace is System, such as System.IO and System.Net. There are other top-level namespaces as well, such as Accessibility and Windows. A user can define a namespace by placing elements inside a namespace block.

Assemblies are the physical packaging of the class libraries. These are .dll files, just like (but not to be confused with) Win32 shared libraries. Examples of assemblies are mscorlib.dll, System.dll, System.Data.dll and Accessibility.dll. Namespaces are often distributed among several assemblies and one assembly can be composed of several files.

Common Language Infrastructure and Common Language Specification

The Common Language Infrastructure (CLI), or more commonly known as the Common Language Runtime, is implemented by the Mono executable. The runtime is used to execute compiled .NET applications. The common language infrastructure is defined by the ECMA standard.[15] To run an application, you must invoke the runtime with the relevant parameters.

The Common Language Specification (CLS) is specified in chapter 6 of ECMA-335 and defines the interface to the CLI, such as conventions like the underlying types for Enum. The Mono compiler generates an image that conforms to the CLS. This is the Common Intermediate Language. The Mono runtime takes this image and runs it. The ECMA standard formally defines a library that conforms to the CLS as a framework.

Managed and unmanaged code

Within a native .NET/Mono application, all code is managed; that is, it is governed by the CLI's style of memory management and thread safety. Other .NET or Mono applications can use legacy code, which is referred to as unmanaged, by using the System.Runtime.InteropServices libraries to create C# bindings. Many libraries which ship with Mono use this feature of the CLI, such as Gtk#.

Related projects

Several projects extend Mono and allow developers to use it in their development environment. These projects include:

Microsoft has a version of .NET 2.0 now available only for Windows XP, called the Shared Source CLI (Rotor). Microsoft's shared source license may be insufficient for the needs of the community (it explicitly forbids commercial use). The Mono project has many of the same goals as the Portable.NET project, part of the similar but separate project DotGNU run by Free Software Foundation.


MonoDevelop is a free GNOME integrated development environment primarily designed for C# and other .NET languages such as Nemerle, Boo, and Java (via IKVM.NET). MonoDevelop was originally a port of SharpDevelop to Gtk#, but it has since evolved to meet the needs of Mono developers. The IDE includes class management, built-in help, code completion, Stetic (a GUI designer), project support, and an integrated debugger.

The MonoDoc browser provides access to API documentation and code samples. The documentation browser uses wiki-style content management, allowing developers to edit and improve the documentation.


MonoTouch allows developers to create C# and .NET based applications that run on the iPhone. It is based on the Mono framework and developed in conjunction with Novell. Unlike Mono applications MonoTouch "Apps" are compiled down to machine code targeted specifically at the Apple iPhone.

MonoTouch is available from Novell under a separate licensing agreement to Mono[16]. MonoDevelop is used as the primary IDE however additional links to XCode and the iPhone simulator have been written.


Mono is dual licensed by Novell, similar to other products such as Qt and the Mozilla Application Suite. Mono's C# compiler and tools are released under the GNU General Public License (GPLv2 only) (starting with version 2.0 of Mono, the Mono C# compiler source code will also be available under the MIT X11 License),[17] the runtime libraries under the GNU Lesser General Public License (LGPLv2 only) and the class libraries under the MIT License. These are all free software and open-source licenses and hence Mono is free and open-source software.

Mono and Microsoft’s patents


Mono’s implementation of those components of the .NET stack not submitted to the ECMA for standardization has been the source of patent violation concerns for much of the life of the project. In particular, discussion has taken place about whether Microsoft could destroy the Mono project through patent suits.

The base technologies submitted to the ECMA, and therefore also the Unix/GNOME-specific parts, may be non-problematic. The concerns primarily relate to technologies developed by Microsoft on top of the .NET Framework, such as ASP.NET, ADO.NET and Windows Forms (see Non standardized namespaces), i.e. parts composing Mono’s Windows compatibility stack. These technologies are today not fully implemented in Mono and not required for developing Mono-applications. Richard Stallman of the Free Software Foundation has stated it may be "dangerous" to use Mono because of the possible threat of Microsoft patents.[18] For this reason, the FSF recommends that people avoid creating free software that depends on Mono or C#.[19]

On November 2, 2006, Microsoft and Novell announced a joint agreement whereby Microsoft agreed to not sue Novell’s customers for patent infringement.[20] According to Mono project leader Miguel de Icaza,[citation needed] this agreement extends to Mono but only for Novell developers and customers. It was criticized by some members of the free software community[who?] because it violates the principles of giving equal rights to all users of a particular program.

In a note posted on the Free Software Foundation's news website in June 2009, Richard Stallman warned that he believes "Microsoft is probably planning to force all free C# implementations underground some day using software patents" and recommended that developers avoid taking what he described as the "gratuitous risk" associated with "depend[ing] on the free C# implementations", including Mono.[21]

On July 6, 2009, Microsoft announced that it was placing their ECMA 334 and ECMA 335 specifications under their Community Promise pledging that they would not assert their patents against anyone implementing, distributing, or using alternative implementations of .NET[22] which have dispelled the patent concerns over the ECMA portions of Mono.

However, the Free Software Foundation later reiterated its warnings,[23] claiming that the extension of Microsoft Community Promise to the C# and the CLI ECMA specifications[24] would not prevent Microsoft from harming open source implementations of C#, because many specific Windows libraries included with .NET or Mono were not covered by this promise.

Software developed with Mono

The following are programs that use the Mono API and C#.

See also


  1. "FAQ: Licensing – Mono". Retrieved 2009-11-26. 
  2. "OSS .NET implementation Mono 1.0 released - Ars Technica". ArsTechnica. Retrieved 2009-10-23. 
  3. "FAQ: General". Mono Project. Retrieved December 4, 2009. 
  5. Olive
  6. Mono Project Roadmap - Mono
  7. "MoonlightRoadmap". Mono Team. Retrieved 2008-11-08. 
  8. "Alpha support for Silverlight 2.0". Retrieved 2009-08-23. "Currently support for Silverlight 2.0 is in pre-Alpha stage" 
  9. Ecma-335
  12. 12.0 12.1 "Compacting GC". Retrieved 2008-12-16. 
  13. Boehm, Hans-J.. "Advantages and Disadvantages of Conservative Garbage Collection". Xerox Parc. Retrieved 2008-12-16. 
  14. .NET Framework Architecture on the official Mono documentation
  15. ECMA-335
  17. "Mono C# Compiler Under MIT X11 License". Novell Inc. 2008-04-08. 
  18. Stallman, Richard (2006-03-09). "Transcript of Richard Stallman on the Free Software movement, Zagreb". Free Software Foundation. Retrieved 2006-11-02. "(...)we know that Microsoft is getting patents on some features of C#. So I think it's dangerous to use C#, and it may be dangerous to use Mono. There's nothing wrong with Mono. Mono is a free implementation of a language that users use. It's good to provide free implementations. We should have free implementations of every language. But, depending on it is dangerous, and we better not do that. " 
  19. Stallman, Richard (2009-06-26). "Why free software shouldn't depend on Mono or C#". Free Software Foundation. Retrieved 2009-07-02. "We should systematically arrange to depend on the free C# implementations as little as possible. In other words, we should discourage people from writing programs in C#. Therefore, we should not include C# implementations in the default installation of GNU/Linux distributions, and we should distribute and recommend non-C# applications rather than comparable C# applications whenever possible." 
  20. Novell (2006-11-02). "Microsoft and Novell Announce Broad Collaboration on Windows and SUSE Linux Interoperability and Support". Press release. Retrieved 2006-11-02. 
  21. Stallman, Richard (June 26, 2009). "Why free software shouldn't depend on Mono or C#". Free Software Foundation. Retrieved July 2, 2009. "The danger is that Microsoft is probably planning to force all free C# implementations underground some day using software patents. ... We should systematically arrange to depend on the free C# implementations as little as possible. In other words, we should discourage people from writing programs in C#. Therefore, we should not include C# implementations in the default installation of GNU/Linux distributions, and we should distribute and recommend non-C# applications rather than comparable C# applications whenever possible." 
  22. "The ECMA C# and CLI Standards". 
  23. "Microsoft's Empty Promise". Free Software Foundation. 2009-07-16. Retrieved 2009-078-03. "Until that happens, free software developers still should not write software that depends on Mono. C# implementations can still be attacked by Microsoft's patents: the Community Promise is designed to give the company several outs if it wants them. We don't want to see developers' hard work lost to the community if we lose the ability to use Mono, and until we eliminate software patents altogether, using another language is the best way to prevent that from happening." 
  24. "The ECMA C# and CLI Standards". 2009-07-06. Retrieved 2009-078-03. 
  25. Mono Launch announced on Second Life Blog Retrieved on 2008-08-30.
  26. Mono Second Life viewer released Retrieved on 2008-08-30.
  27. Something Awful: The Internet Makes You Stupid



External links


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