When Microsoft first announced their .NET Framework in June 2000 it was described as "a new platform based on Internet standards",[5] and in December of that year the underlying Common Language Infrastructure was published as an open standard, "ECMA-335",[6] opening up the potential for independent implementations.[7]Miguel de Icaza of Ximian believed that .NET had the potential to increase programmer productivity and began investigating whether a Linux version was feasible.[8] Recognizing that their small team could not expect to build and support a full product, they launched the Mono open-source project, on July 19, 2001, at the O'Reilly conference.
After three years of development, Mono 1.0 was released on June 30, 2004.[9] Mono evolved from its initial focus of a developer platform for Linux desktop applications to supporting a wide range of architectures and operating systems - including embedded systems.[10]
Novell acquired Ximian in 2003. After Novell was acquired by Attachmate in April 2011, Attachmate announced hundreds of layoffs for the Novell workforce,[11] putting in question the future of Mono.[12][13]
On May 16, Miguel de Icaza announced in his blog that Mono would continue to be supported by Xamarin, a company he founded after being laid off from Novell. The original Mono team had also moved to the new company. Xamarin planned to keep working on Mono and had planned to rewrite the proprietary .NET stacks for iOS and Android from scratch, because Novell still owned MonoTouch and Mono for Android at the time.[14] After this announcement, the future of the project was questioned, MonoTouch and Mono for Android being in direct competition with the existing commercial offerings now owned by Attachmate, and considering that the Xamarin team would have difficulties proving that they did not use technologies they formerly developed when they were employed by Novell for the same work.[15] However, in July 2011, Novell, now a subsidiary of Attachmate, and Xamarin, announced that it granted a perpetual license to Xamarin for Mono, MonoTouch and Mono for Android, which officially took stewardship of the project.[16][17]
Current status and roadmap
Mono's current version is 6.0.0 (as of August 2019[update]). This version provides the core API of the .NET Framework and support for Visual Basic.NET and C# 7.0. LINQ to Objects, XML, and SQL are part of the distribution. Windows Forms 2.0 is also supported, but not actively developed, and as such its support on Mono is incomplete.[18] Version 4.0 was the first version that incorporates Microsoft original source code that was released by Microsoft as part of the .NET Core project.
As of January 14, 2021, Mono has full support for all the features in .NET 4.7 except Windows Presentation Foundation (WPF) (which the Mono team do not plan to support due to the amount of work it would need)[18] and Windows Workflow Foundation (WF), and with only limited support for Windows Communication Foundation (WCF) and the ASP.NET async stack. However, System.Web and WCF are candidates for 'almost immediate' porting from the .NET reference source back to Mono.[19] Some missing parts of the .NET Framework are under development in an experimental Mono subproject called Olive.[20]
The Mono project has also created a Visual Basic .NET compiler and a runtime designed for running VB.NET applications. It is currently being developed by Rolf Bjarne Kvinge.
An open-source implementation of Microsoft Silverlight, called Moonlight, has been included since Mono 1.9.[21] 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.[22] A preview release of Moonlight 3.0 was announced in February 2010 and contains updates to Silverlight 3 support.[23]
The Moonlight project was abandoned on May 29, 2012.[24] According to Miguel, two factors sealed the fate of the project: Microsoft added "artificial restrictions" that "made it useless for desktop programming", and the technology had not gained enough traction on the Web. In addition, Silverlight itself was deprecated by Microsoft by 2012.
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 graphical user interface (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 the object-relational database db4o, Firebird, Microsoft SQL Server (MSSQL), MySQL, Open Database Connectivity (ODBC), Oracle, PostgreSQL, SQLite, and many others. The Mono project tracks developing database components at its website.[27]
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.
The Mono runtime contains a code execution engine that translates ECMA CIL byte codes into native code and supports a number of processors: ARM, MIPS (in 32-bit mode only), SPARC, PowerPC, z/Architecture, IA-32, x86-64 and IA-64 for 64-bit modes.
The code generator is exposed in three modes:
Just-in-time (JIT) compilation: The runtime will turn ECMA CIL byte codes into native code as the code runs.
Ahead-of-Time (AOT) 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 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 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.[citation needed]
Starting with Mono 2.6, it is possible to configure Mono to use the 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 no 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-starting Mono code generation engine.
Starting with Mono 5.18, support for LLVM is a default configuration option. Previous versions required a special LLVM fork, but now mono can fall back to its own code generator when it encounters something not handled by LLVM.[28]
Garbage collector
As of Mono 2.8, the Mono runtime ships with two garbage collectors: a generational collector and the Boehm-Demers-Weiser Conservative Garbage Collector. The Boehm garbage collector could exhibit memory leaks on certain classes of applications, making it unsuitable for some long-running server applications.[29][30] Mono switched to Simple Generational GC (SGen-GC) as the default collector in version 3.1.1.
The SGen garbage collector has many advantages over a traditional conservative scanner. It uses generational garbage collection where new objects are allocated from a nursery, during the garbage collection cycle, all objects that survived are migrated to an older generation memory pool. The idea is that many objects are transient and can quickly be collected and only a handful of objects are long-term objects that live for the entire life of the application. To improve performance this collector assigns memory pools to each thread to let threads allocate new memory blocks without having to coordinate with other threads. Migration of objects from the nursery to the old generation is done by copying the data from the nursery to the old generation pool and updating any live pointers that point to the data to point to the new location. This can be expensive for large objects, so Mono's SGen uses a separate pool of memory for large objects (Large Object Section) and uses a mark-and-sweep algorithm for those objects.[29]
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.[31]
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) as implemented by the Common Language Runtime (CLR), is implemented by the Mono executable. The runtime compiles and executes .NET applications. The common language infrastructure is defined by the ECMA standard.[25] 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).[32]
SIMD support[34] 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[35] (used on Mono/iPhone, Mono/PS3).
Cxxi and CppSharp direct interop with C++ code and libraries.
In addition, Mono is available on a variety of operating systems and architectures.[38]
System requirements
Windows 7, Windows 8, Windows 8.1, Windows 10, macOS or Linux
Related projects
Several projects extend Mono and allow developers to use it in their development environment. These projects include:
Cross-platform:
Banshee Media Player (stalled), 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.
Beagle (unmaintained), a search system for Unix systems.
Gecko#, bindings for embedding the layout engine used in Mozilla (Gecko).
Gtk#, C# wrappers around the underlying GTK and GNOME libraries, written in C and available on Linux, MacOS and Windows.
Mono Migration Analyzer (MoMA), a tool which aids Windows .NET developers in finding areas in their code that might not be cross-platform and therefore not work in Mono on Linux and other Unixes. Not upgraded since Mono 2.8 (2013); use Microsoft's .NET Portability Analyzer (dotnet-apiport) instead.
MonoCross, a cross-platform model–view–controller design pattern where the Model and Controller are shared across platforms and the Views are unique for each platform for an optimized User Interface. The framework requires Xamarin.iOS and Xamarin.Android.
MvvmCross, a cross-platform Model View ViewModel framework utilizing Xamarin.iOS and Xamarin.Android for developing mobile apps.
MonoDevelop an open-source and cross-platform integrated development environment that supports building applications for ASP.NET, Gtk#, Meego, MonoTouch and Silverlight/Moonlight.
Resco MobileBusiness, a cross-platform developer solution for mobile clients.
Resco MobileCRM, a cross-platform developer solution for mobile clients synchronized with Microsoft Dynamics CRM.
ServiceStack a high-performance open-source .NET REST web services framework that simplifies the development of XML, JSON and SOAP web services.
SparkleShare an open-source client software that provides cloud storage and file synchronization services.
Tao (superseded by OpenTK), a collection of graphics and gaming bindings (OpenGL, SDL, GLUT, Cg).
Xwt, a GUI toolkit that maps API calls to native platform calls of the underlying platform, exposing one unified API across different platforms and making possible for the graphical user interfaces to have native look and feel on different platforms. It enables building GUI-based desktop applications that run on multiple platforms, without having to customizing code for different platforms. Xwt API is mapped to a set of native controls on each supported platform. Features that are not available on specific platforms are emulated by using native widgets, which is referred to as hosting in the Xwt context.[39] Xwt was partially used as GUI toolkit (beside GTK#) in the development of the Xamarin Studio.[40] Supported "backend" engines are: WPF engine and Gtk engine (using Gtk#) on Windows, Cocoa engine (using MonoMac) and Gtk engine (using Gtk#) on Mac OS X, and Gtk engine (using Gtk#) on Linux.[41]
macOS:
Cocoa# – wrappers around the native macOS toolkit (Cocoa) (deprecated).
Monobjc – a set of bindings for macOS programming.
MonoMac – newer bindings for macOS programming, based on the MonoTouch API design.
Mobile platforms:
MonoDroid. Mono for the Android operating system. With bindings for the Android APIs.
MonoTouch. Mono for the iPhone, iPad and iPod Touches. With bindings to the iOS APIs.
Windows:
MonoTools for Visual Studio A Visual Studio plugin that allows Windows developers to target Linux and macOS right from Visual Studio and integrates with SUSE Studio.
Other implementations
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).
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, 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.
Xamarin.iOS and Xamarin.Android
Xamarin.iOS and Xamarin.Android, both developed by Xamarin, are implementations of Mono for iPhone and Android-based smartphones. Previously available only for commercial licensing,[43] after Microsoft's acquisition of Xamarin in 2016, the Mono runtime itself was relicensed under MIT license[44] and both Xamarin.iOS and Xamarin.Android are being made free and open-source.[45]
Xamarin.iOS
Xamarin.iOS (previously named MonoTouch) is a library that allows developers to create C# and .NET based applications that run on the iPhone, iPod and iPad devices. It is based on the Mono framework and developed in conjunction with Novell. Unlike Mono applications, Xamarin.iOS "Apps" are compiled down to machine code targeted specifically at the AppleiPhone and iPad.[46] This is necessary because the iOS kernel prevents just-in-time compilers from executing on the device.
The Xamarin.iOS stack is made up of:
Compilers
C# from the Mono Project
Third-party compilers like RemObject's Oxygene can target Xamarin.iOS also
Core .NET libraries
Development SDK:
Linker – used to bundle only the code used in the final application
mtouch – the Native compiler and tool used to deploy to the target device
Xamarin Studio is used as the primary IDE, however additional links to Xcode and the iOS simulator have been written.
From April to early September 2010, the future of MonoTouch was put in doubt as Apple introduced new terms 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 iOS platform and iPhone applications. This made the future of MonoTouch, and other technologies such as Unity, uncertain.[47] Then, in September 2010, Apple rescinded this restriction, stating that they were relaxing the language restrictions that they had put in place earlier that year.[48][49]
Xamarin.Android (formerly known as Mono for Android), initially developed by Novell and continued by Xamarin, is a proprietary[citation needed][66] implementation of Mono for Android-based smart-phones.[67][68][69] It was first released on April 6, 2011.[70] Mono for Android was developed to allow developers to more easily write cross-platform applications that will run on all mobile platforms.[71] In an interview with H-Online, Miguel de Icaza stated, "Our vision is to allow developers to reuse their engine and business logic code across all mobile platforms and swapping out the user interface code for a platform-specific API."[72]
In August 2010, a Microsoft spokesman, Tom Hanrahan of Microsoft's Open Source Technology Centre, stated, in reference to the lawsuit filed by Oracle against Google over Android's use of Java, that "The type of action Oracle is taking against Google over Java is not going to happen. If a .NET port to Android was through Mono it would fall under the Microsoft Community Promise Agreement."[73][74]
The Xamarin.Android stack consists of the following components:
Xamarin Studio and Visual Studio 2010 integration to design the UI, remotely debug, and deploy.
Mono on macOS
CocoaSharp
Cocoa# (also known as CocoaSharp) was a bridge framework for Mac OS X, which allowed applications developed with the Mono runtime to access the Cocoa API. It was initially released on August 12, 2004,[76] and was included with the Mono distribution starting with version 1.0.6, released on February 18, 2005.[citation needed] It has not seen any development since 2008,[citation needed] and is now deprecated.[77]
Monobjc
Monobjc was CocoaSharp's replacement. It allows .NET developers to use most of the Mac OS X API, including Cocoa, with no native code, while still achieving a native UI.[citation needed]
Xamarin.Mac
Xamarin.Mac is a library that allows developers to run .NET and C# apps on the Mac.[78]
The license of the C# compiler was changed from the GPL to the MIT X11 license[80] to allow the compiler code to be reused in a few instances where the GPL would have prevented such:
Mono's Compiler as a Service
The Mono interactive Shell
The Mono embeddable C# compiler
Mono's implementation of the C# 4.0 dynamic binder.
On March 18, 2016, Microsoft's acquisition of Xamarin was officially closed.[81]
On March 31, 2016, Microsoft announced at Microsoft Build that they'll completely re-license Mono under the MIT License even in scenarios where previously a commercial license was necessary,[82] and Microsoft stated that they won't assert any "applicable patents" against parties that are "using, selling, offering for sale, importing, or distributing Mono."[83][84] It was also announced that Xamarin had contributed the Mono Project to the .NET Foundation.[83]
Mono's APIs are now in par with .NET 2.0. Introduces the C# 3.0 and Visual Basic 8 compilers. New Mono-specific APIs: Mono.Cecil, Mono.Cairo and Mono.Posix. Gtk# 2.12 is released. The Gendarme verification tool and Mono Linker are introduced.
Mono switches its JIT engine to a new internal representation[94] that gives it a performance boost and introduces SIMD support in the Mono.Simd[34] Mono.Simd namespace. Mono introduces Full Ahead of Time compilation that allows developers to create full static applications and debuts the C# Compiler as a Service[32] and the C# Interactive Shell[33] (C# REPL)
The Mono runtime is now able to use LLVM as a code generation backend and this release introduces Mono co-routines, the Mono Soft Debugger and the CoreCLR security system required for Moonlight and other Web-based plugins. On the class library System.IO.Packaging, WCF client, WCF server, LINQ to SQL debut. The Interactive shell supports auto-completion and the LINQ to SQL supports multiple database backends. The xbuild build system is introduced.
Defaults to .NET 4.0 profile, C# 4.0 support, new generational garbage collector, includes Parallel Extensions, WCF Routing, CodeContracts, ASP.NET 4.0, drops the 1.0 profile support; the LLVM engine tuned to support 99.9% of all generated code, runtime selectable llvm and gc; incorporates Dynamic Language Runtime, MEF, ASP.NET MVC2, OData Client open-source code from Microsoft;. Will become release 3.0
Shipping Roslyn C# compiler to enable C#7 support; Shipping msbuild and deprecating xbuild for better compatibility; Enabling concurrent SGen garbage collector to reduce time spent in GC; Introducing the AppleTLS stack on macOS for HTTPS connections; Continued Progress on .NET Class Library convergence; Updated libjpeg in macOS package
The Interpreter is now included in the default installation; runtime now supports Default Interface Methods; WebAssembly considered reliable now; Support for .NET 4.7.1 / C# 7.2 / F# 4.1
^"The Death and Rebirth of Mono". infoq.com. 2011-05-17. Retrieved 2011-05-29. Even if they aren't supporting it, they do own a product that is in direct competition with Xamarin's future offerings. Without some sort of legal arrangement between Attachmate and Xamarin, the latter would face the daunting prospect of proving that their new development doesn't use any the technology that the old one did. Considering that this is really just a wrapper around the native API, it would be hard to prove you had a clean-room implementation even for a team that wasn't intimately familiar with Attachmate's code.
^"SUSE and Xamarin Partner to Accelerate Innovation and Support Mono Customers and Community". Novell. 2011-07-18. Retrieved 2011-07-18. The agreement grants Xamarin a broad, perpetual license to all intellectual property covering Mono, MonoTouch, Mono for Android and Mono Tools for Visual Studio. Xamarin will also provide technical support to SUSE customers using Mono-based products, and assume stewardship of the Mono open source community project.
^ abde Icaza, Miguel (2011-03-07). "GDC 2011". Retrieved 2011-03-11. We have no plans on building WPF. We just do not have the man power to build an implementation in any reasonable time-frame(...)For tools that are mostly OpenGL/DirectX based, use Windows.Forms, keeping in mind that some bug fixing or work around on their part might be needed as our Windows.Forms is not actively developed.
^"Xamarin for Everyone". blog.xamarin.com. 2016-03-31. we are announcing today our commitment to open source the Xamarin SDKs for Android, iOS, and Mac under the MIT license in the coming months
^"MonoTouch and iPhone 4". Applications built with MonoTouch are native applications indistinguishable from other native applications.
^"Statement by Apple on App Store Review Guidelines". Based on their input, today we are making some important changes to our iOS Developer Program license in sections 3.3.1, 3.3.2 and 3.3.9 to relax some restrictions we put in place earlier this year. In particular, we are relaxing all restrictions on the development tools used to create iOS apps, as long as the resulting apps do not download any code. This should give developers the flexibility they want, while preserving the security we need.
^"Great News for MonoTouch Users". With these new terms, the ambiguity is gone and C# lovers and enthusiasts can go back to using MonoTouch. Developers that like garbage collection and their strongly typed languages can resume their work.
^"Novell (Mono/C#) is developing MonoDroid". Android Community. 18 February 2010. This will make it easier for developers to make cross platform apps as well as bring some of the existing apps that are made using MonoTouch to Android.
^"Mono for Android". H-Online. Our vision is to allow developers to reuse their engine and business logic code across all mobile platforms and swapping out the user interface code for a platform-specific API.
^"Microsoft won't stop (Mono) .NET on Android". TechWorld. The type of action Oracle is taking against Google over Java is not going to happen. If a .NET port to Android was through Mono it would fall under the Microsoft Community Promise Agreement.
