Mono 2.8 - New GC, C# 4.0, and LLVM

Ten months worth of development has brought plenty of major updates and new features to the open source implementation of the .NET framework, Mono.  Today, Mono 2.8 adds support for C# 4.0, a new Garbage Collection engine, System.XAML, the Parallel Framework, ASP.NET MVC 2, ASP.NET 4.0, OpenBSD, and more.  Mono 2.8 has also graduated LLVM support to 'stable' and made large performance improvements.

ABI/API Embedding

Mono 2.8 no longer depends on the GLIB library.  2.8 has removed internal methods from the public API and replaced GLIB types with integer data types from stdint.h.  Project developers also depreciated some methods that were limited and not intended for external use.

New GC

Mono has been using an excellent GC written by Hans Boehm for years, but with 2.8 the developers wanted to add less conservative features like generational garbage collection.  The project decided to change its GC to SGen: a generational, copying, heap precise, stack conservative garbage collector. SGen can repack the data in memory and it can also move data around in a way that reduces heap fragmentation.  The .NET-based graph database, Sones, did some benchmarking of SGen vs. Mono's old garbage collector:



The blue line is the time it takes SGen to fulfill a request while the red line is the Boehm GC.  SGen is supported on ARM, x86, x86-64 and the s390x platforms.

New MS-PL or Apache v2-licensed Microsoft Libraries

• ASP.NET MVC2
• Managed Extensibility Framework (MEF)
• System.Data.Services.Client
• Dynamic Language Runtime

LLVM

Support for the Low-Level Virtual Machine compiler infrastructure is now stable in 2.8.  Users can write a mono-llvm command to make server applications run with an LLVM backend.  However, JIT compilation with this release is still quite slow, so the backend is currently suitable for long server processes only.

Other new features

Mono 2.8 introduces a partial implementation of Code Contracts, a preview code implementation of PLinq, the Managed Extensibility Framework, and the Dynamic Language Runtime.  XBuild is also available now for building Silverlight projects and WCF routing has been added.

Miguel De Icaza, the Mono project lead, reminds us that Mono 2.6 is still the long term support release.  The next long term version will be Mono 3.0.