Mono (software)

Mono

Developer(s)	Novell
Initial release	June 30, 2004
Stable release	2.6.7 / July 19, 2010; 6 months ago (2010-07-19)
Operating system	Cross-platform
Type	Platform
License	GPLv2, LGPLv2 and MIT, or dual license[1]
Website	www.mono-project.com

Mono, pronounced [moʊ'noʊ], 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, iOS, Android, Solaris and Windows operating systems as well as some game console operating systems such as the ones for the PlayStation 3, XBox 360 and Wii.

History

Lacking the resources to build a full .NET replacement on their own, Ximian 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.^[15] Being an open source project, the runtime evolved from a primary focus of being a developer platform for Linux desktop application to go into the server (with ASP.NET) to support a plurality of architectures and operating systems, to embedded systems.

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."^[16]

Current status and roadmap

Mono's current version is 2.6.7 (as of July 2010^[update]). 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, XML, and SQL are part of the distribution. 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^[update]) but not yet released in a stable version.^[17]

Parts of the .NET Framework 3.0 are under development in an experimental Mono subproject called "Olive", but the availability of WPF is not yet planned.^[18][19] The Windows Communication Foundation stack for clients and servers have graduated from Olive and been incorporated into the main Mono distribution.

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.

Moonlight

An open source implementation of Silverlight, called Moonlight, has been included since Mono 1.9.^[20] Moonlight 1.0, which supports the Silverlight 1.0 APIs, was released January 20, 2009. Moonlight 2.0 supports Silverlight 2.0 and some features of Silverlight 3.0.^[21] A preview release of Moonlight 3.0 was announced in February 2010 and contains updates to Silverlight 3 support.^[22]

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# compiler, the virtual machine for the Common Language Infrastructure and the core class libraries. These components are based on the Ecma-334 and Ecma-335 standards,^[23] 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.^[24]

The Mono/Linux/GNOME development stack provide tools for application development while using the 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 (Mono.Posix), 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.^[25]

The Microsoft compatibility stack provides a pathway for porting Windows .NET applications to GNU/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

Simplified Mono architecture

Code Execution Engine

The Mono runtime contains a code execution engine that translates ECMA CIL byte codes into native code and supports a number of processors: MIPS (in 32-bit mode only), SPARC, PowerPC, ARM, S390 (in 32-bit and 64-bit mode), x86, x86-64 and IA-64 for 64-bit modes.

The code generator is exposed in three modes:

• Just in time compilation: The runtime will turn ECMA CIL byte codes into native code as the code runs.
• Ahead-of-Time compilation: this code turns the ECMA CIL byte codes (typically found on a .exe or .dll file) and generates native code stored in an operating system, architecture and CPU specific file (for a foo.exe file, it would produce foo.exe.so on Linux). This mode of operation compiles most of the code that is typically done at runtime. There are some exceptions like trampolines and other administrative bits of code that still require the JIT to function, so AOT images are not fully standalone.
• Full Static Compilation: this mode is only supported on a handful of platforms and takes the Ahead-of-Time compilation process one step further and generates all the trampolines, wrappers and proxies that are required into a static file that can be statically linked into a program and completely eliminates the need for a JIT at runtime. This is used on Apple's iOS, Sony's PlayStation 3 and Microsoft's XBox 360 operating systems.

Starting with Mono 2.6, it is possible to configure Mono to use the Low Level Virtual Machine (LLVM) as the code generation engine instead of Mono's own code generation engine. This is useful for high performance computing loads and other situations where the execution performance is more important than the startup performance.

Starting with the Mono 2.7 preview, it is not longer necessary to pick one engine over the other at configuration time. The code generation engine can be selected at startup by using the --llvm or --nollvm command line arguments, and it defaults to the fast Mono code generation engine.

Garbage Collector

The current default garbage collector (the "Boehm-Demers-Weiser Conservative Garbage Collector")^[26][27] has significant limitations compared to commercial garbage-collected runtimes like the Java Virtual Machine or the .NET framework's runtime, such as a conservative garbage collection can exhibit memory leaks that make it unsuitable for long-running server applications.

As of July 2009^[update], development of a modern garbage collector called "Simple Generational GC" (SGen-GC) is under way and is now bundled as part of Mono 2.7. Just like the LLVM code generation engine is now selectable at startup, users can elect to use the new SGen garbage collector by passing the --gc=sgen switch to the Mono runtime at startup.^[26]

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.^[28]

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.^[29] 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#.

Mono Specific Innovations

Mono has innovated in some areas with new extensions to the core C# and CLI specifications:

• C# Compiler as a Service (Use the C# compiler as a library) ^[30]
• C# Interactive Shell^[11]
• SIMD support^[9] as part of the Mono.SIMD namespace, where method calls to special vector types are directly mapped to the underlying processor CPU SIMD instructions.
• Full Static Compilation of .NET code^[31] (used on Mono/iPhone, Mono/PS3).
• Mono coroutines (used to implement micro-threading code and continuations, mostly for game developers)^[32]
• 64-bit "large arrays", although present on the ECMA specification, Mono is the only implementation that supports them.
• Assembly injection to live processes^[33]
• Use of LLVM as JIT backend

In addition, Mono is available on a variety of operating systems and architectures^[34]

Related projects

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

Cross-Platform:

• Moonlight, an implementation of Silverlight that uses Mono
• MonoDevelop an open source and cross platform Integrated Development Environment that supports building applications for ASP.NET, Gtk#, Meego, MonoTouch and Silverlight/Moonlight.
• Gtk#, C# wrappers around the underlying GTK+ and GNOME libraries, written in C and availble on Linux, MacOS and Windows.
• Banshee Media Player a cross-platform music media player built with Mono and Gtk# and also a driver of dozens of C#-based libraries and projects for media handling.
• Gecko#, bindings for embedding the layout engine used in Mozilla (Gecko)
• Qyoto, C# bindings for the Qt framework
• Mono Migration Analyzer (MoMA), a tool which aids Windows .NET developers in finding areas in their code that might not be cross-platform and therefor not work in Mono on Linux and other Unixes.
• Tao, a collection of graphics and gaming bindings (OpenGL, SDL, Glut, Cg)

MacOS:

• Cocoa# wrappers around the native Mac OS X toolkit (Cocoa) (deprecated)
• MonoMac the new bindings for OSX programming, based on the MonoTouch API design.

Mobile Platforms:

• MonoTouch Mono for the iPhone, iPad and iPod Touches. With bindings to the iOS APIs.
• MonoDroid Mono for the Android operating system. With bindings for the Android APIs.

Windows:

• MonoTools for Visual Studio A Visual Studio plugin that allows Windows developers to target Linux, MacOS right from Visual Studio and integrates with SUSE Studio.

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

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), although it also supports languages such as C, C++, Python, Java, and Vala. 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

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.^[39] MonoDevelop is used as the primary IDE however additional links to Xcode and the iPhone simulator have been written.

In April 2010, Apple introduced a new term for iPhone developers that apparently prohibits them from developing in languages other than C, C++ and Objective-C, and the use of a middle layer between the iPhone OS platform and iPhone applications. This makes the future of MonoTouch, as well as other technologies such as UNITY, uncertain.^[40]

License

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),^[41] 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. Over the lifetime of the project these concerns have proven to be unfounded.^[42]

The base technologies submitted to the ECMA, and therefore also the Unix/GNOME-specific parts, are not problematic due to Microsoft's explicitly placing both ECMA 334 and ECMA 335 standards under the Microsoft Community Promise. 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, they are simply there for developers and users who need full compatibility with the Windows system.

Should patent issues ever arise, the Mono project's stated strategy for dealing with them is as follows:^[43]

• Work around the patent by using a different implementation technique that retains the API, but changes the mechanism; if that is not possible, they would
• Remove the pieces of code that were covered by those patents, and also
• Find prior art that would render the patent useless.

In addition, Mono is also included in the list of software that the Open Invention Network has sworn to protect.^[44]

Free Software Foundation's warnings

Richard Stallman of the Free Software Foundation has stated it may be "dangerous" to use Mono because of the possible threat of Microsoft patents.^[45] For this reason, the FSF recommends that people avoid creating free software that depends on Mono or C#.^[46]

On November 2, 2006, Microsoft and Novell announced a joint agreement whereby Microsoft agreed to not sue Novell’s customers for patent infringement.^[47] Under the agreement, patent protections extends to Mono but only for Novell developers and customers.^[48] It was criticized by some members of the free software community 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.^[49]

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.^[50] However, their position regarding the non-ECMA components like ASP.NET, ADO.NET, and Windows Forms (which are the bone of contention) remains unclarified.

Subsequently, the Free Software Foundation reiterated its warnings,^[51] claiming that the extension of Microsoft Community Promise to the C# and the CLI ECMA specifications^[52] 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, examples include regular expressions and XML which the FSF considers now dangerous to use.^[53]

These warnings, however, were countered by Miguel de Icaza, lead developer of Mono, on the GNOME Foundation mailing-list,^[54] saying "That article now leads us to believe that there is something "magical" about the way that Microsoft implements regular expressions or how they implemented XSLT and XPath. If you can't find prior art for that, you probably should leave the software industry while you are still ahead."

Canonical Ltd., makers of the Ubuntu (Operating System) Linux distribution, have also come out with a Mono Position Statement^[55] which states that "It is common practice in the software industry to register patents as protection against litigation, rather than as an intent to litigate. Thus mere existence of a patent, without a claim of infringement, is not sufficient reason to warrant exclusion from the Ubuntu Project." The statement then goes on to say that they would therefore continue to ship Mono in Ubuntu until the patents actually become a real threat rather than simply a perceived threat.

Fedora Project Leader, Paul Frields, has stated that "We haven't come to a legal conclusion that is pat enough for us to make the decision to take mono out." ^[56]

Software developed with Mono

Banshee (media player)

GNOME Do

A range of the programs have been developed that use the Mono API and C#. Some such programs written for the Linux Desktop include Banshee, Beagle, F-Spot, Gbrainy, GNOME Do, MonoTorrent, Pinta, and Tomboy. A number of video games such as The Sims 3 and Second Life along with many games based on the Unity game engine also make use of Mono.

See also

• Comparison of application virtual machines
• MonoDevelop - an open source IDE targeting both Mono and Microsoft .NET framework platforms
• DotGNU - A completely free software implementation of ECMA standard .NET
• Portable.NET - A portable version of DotGNU toolchain and runtime
• Common Language Runtime
• Shared Source Common Language Infrastructure - Microsoft's shared source implementation of .NET, previously codenamed Rotor
• mod_mono - a module for the Apache HTTP Server that allows for hosting of ASP.NET pages and other assemblies on multiple platforms by use of the Mono

Notes

References

• This article incorporates text from Mono's homepage, which was then under the GNU Free Documentation License.
• Miguel de Icaza (October 13, 2003). "[Mono-list] Mono early history." (mailing list). http://lists.ximian.com/archives/public/mono-list/2003-October/016345.html. Retrieved December 6, 2005. 
• Edd Dumbill (March 11, 2004). "Will Mono Become the Preferred Platform for Linux Development?". ONLamp. http://www.onlamp.com/pub/a/onlamp/2004/03/11/mono.html. Retrieved October 14, 2006. 
• Eugenia Loli-Queru (February 22, 2005). "Mono Applications? Aplenty!". OSNews. http://www.osnews.com/story.php?news_id=9780. Retrieved December 6, 2005. 
• Sean Michael Kerner (November 18, 2005). "Mono Project Goes Virtual". Internet News. http://www.internetnews.com/dev-news/article.php/3565496. Retrieved October 14, 2006. 
• Kerner, Sean Michael (November 9, 2006). "Months Late, Novell Ships Mono 1.2". internetnews.com. http://www.internetnews.com/dev-news/article.php/3643026. 
• Corey Northcutt (October 12, 2006). "In the World of mod_mono". Ubiquity. http://blog.ubiquityhosting.com/?p=34. Retrieved October 14, 2006. 
• Sean Campbell (October 8, 2008). "Interview with Joseph Hill - Product Manager - Mono - Novell". HSIB. http://howsoftwareisbuilt.com/2008/10/08/interview-with-joseph-hill-mono/. Retrieved October 8, 2008. 

External links

• Mono Project Main Page
• MonoTouch Main Page
• Taking the new and shiny Mono Simple Generational Garbage Collector for a walk - A performance comparison of the Boehm GC and Mono's new SGEN GC.