What is new in Common Language Runtime (CLR) 4.0

The following sections describe new features in security, parallel computing, performance and diagnostics, dynamic language runtime, and other CLR-related technologies.
Security

The .NET Framework 4 Beta 1 provides simplifications, improvements, and expanded capabilities in the security model. For more information, see Security Changes in the .NET Framework 4.
Parallel Computing

The .NET Framework 4 Beta 1 introduces a new programming model for writing multithreaded and asynchronous code that greatly simplifies the work of application and library developers. The new model enables developers to write efficient, fine-grained, and scalable parallel code in a natural idiom without having to work directly with threads or the thread pool. The new Parallel and Task classes, and other related types, support this new model. Parallel LINQ (PLINQ), which is a parallel implementation of LINQ to Objects, enables similar functionality through declarative syntax. For more information, see Parallel Programming in the .NET Framework.
Performance and Diagnostics

In addition to the following features, the .NET Framework 4 Beta 1 provides improvements in startup time, working set sizes, and faster performance for multithreaded applications.
ETW Events

You can now access the Event Tracing for Windows (ETW) events for diagnostic purposes to improve performance. For more information, see the following topics:

    *

      CLR ETW Events
    *

      Using Event Tracing for Windows to Log CLR Events

Performance Monitor (Perfmon.exe) now enables you to disambiguate multiple applications that use the same name and multiple versions of the common language runtime loaded by a single process. This requires a simple registry modification. For more information, see Performance Counters and In-Process Side-By-Side Applications.
Code Contracts

Code contracts let you specify contractual information that is not represented by a method's or type's signature alone. The new System.Diagnostics.Contracts namespace contains classes that provide a language-neutral way to express coding assumptions in the form of pre-conditions, post-conditions, and object invariants. The contracts improve testing with run-time checking, enable static contract verification, and documentation generation.

The applicable scenarios include the following:

    *

      Perform static bug finding, which enables some bugs to be found without executing the code.
    *

      Create guidance for automated testing tools to enhance test coverage.
    *

      Create a standard notation for code behavior, which provides more information for documentation.

Lazy Initialiation

With lazy initialization, the memory for an object is not allocated until it is needed. Lazy initialization can improve performance by spreading object allocations evenly across the lifetime of a program. You can enable lazy initialization for any custom type by wrapping the type inside a System..::.Lazy<(Of <(T>)>) class.
Dynamic Language Runtime

The dynamic language runtime (DLR) is a new runtime environment that adds a set of services for dynamic languages to the CLR. The DLR makes it easier to develop dynamic languages to run on the .NET Framework and to add dynamic features to statically typed languages. To support the DLR, the new System.Dynamic namespace is added to the .NET Framework. In addition, several new classes that support the .NET Framework infrastructure are added to the System.Runtime.CompilerServices namespace. For more information, see Dynamic Language Runtime Overview.
In-Process Side-by-Side Execution

In-process side-by-side hosting enables an application to load and activate multiple versions of the common language runtime (CLR) in the same process. For example, you can run applications that are based on the .NET Framework 2.0 SP1 and applications that are based on .NET Framework 4 Beta 1 in the same process. Older components continue to use the same CLR version, and new components use the new CLR version. For more information, see Hosting Changes in the .NET Framework 4.
Interoperability

New interoperability features and improvements include the following:

    *

      You no longer have to use primary interop assemblies (PIAs). Compilers embed the parts of the interop assemblies that the add-ins actually use, and type safety is ensured by the common language runtime.
    *

      You can use the System.Runtime.InteropServices..::.ICustomQueryInterface interface to create a customized, managed code implementation of the IUnknown::QueryInterface method. Applications can use the customized implementation to return a specific interface (except IUnknown) for a particular interface ID.

Profiling

In the .NET Framework 4 Beta 1, you can attach profilers to a running process at any point, perform the requested profiling tasks, and then detach. For more information, see the [IClrProfiling::AttachProfiler]IClrProfiling Interface::AttachProfiler Method method.
Garbage Collection

The .NET Framework 4 Beta 1 provides background garbage collection; for more information, see the entry So, what’s new in the CLR 4.0 GC? in the CLR Garbage Collector blog. 
Covariance and Contravariance

Several generic interfaces and delegates now support covariance and contravariance. For more information, see Covariance and Contravariance in the Common Language Runtime.