Hosting Overview
.NET Framework applications automatically host the common language runtime that they were built against. If you compile your managed code as an .exe assembly, the runtime is started automatically by mscoree.dll when the .exe is run. Unmanaged applications can also benefit from hosting the common language runtime. The runtime provides a framework for extending applications such as Internet Information Services (IIS) and SQL Server 2005.
Whether it is invoked automatically, as with managed .exe assemblies, or loaded by using the unmanaged hosting API, a .NET Framework application requires a piece of code called a runtime host. The runtime host loads the runtime into a process, creates application domains within the process, and loads and executes user code within those application domains.
The .NET Framework version 2.0 enables applications that host the CLR to control many features of the runtime. You can replace some features, such as memory allocation and assembly loading, with custom implementations. You can control the behavior of other features, receive notifications of events in the runtime, and manage application domains.
The .NET Framework version 4 consolidates many of the version 2.0 hosting APIs. In addition, .NET Framework 4 supports in-process side-by-side runtime host activation, and provides other enhancements.
This overview contains the following sections:
Initializing and Starting a Hosted Runtime
.NET Framework version 2.0 Hosting Management Interfaces
.NET Framework version 4 Hosting Management Interfaces
Application Domain Managers
Related Topics
Reference
Initializing and Starting a Hosted Runtime
The .NET Framework 4 hosting API provides the CLRCreateInstance function, which can return the ICLRMetaHost interface. You can then call the GetRuntime method on this interface to get a specific ICLRRuntimeInfo interface, given a particular CLR version. This procedure supersedes the CorBindToRuntimeEx method that is used by the .NET Framework 2.0 hosting API.
The .NET Framework version 2.0 hosting API provides the CorBindToRuntimeEx function to initialize the runtime. You can choose which version of the runtime to load, but a process can host only one version. If version 2.0, 3.0, or 3.5 is loaded, the function returns the ICLRRuntimeHost interface, which is used to start the runtime and execute managed code.
The .NET Framework version 1 hosting API provides the ICorRuntimeHost interface.
Starting the runtime is discussed in Loading the Common Language Runtime into a Process, and executing managed code is discussed in Transitioning to Managed Hosting Code.
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.NET Framework 2.0 Hosting Management Interfaces
In the .NET Framework 2.0, the CLR provides hosting management interfaces to control many features of the hosted runtime, enables the host application to implement other management interfaces provided by the runtime, and lets you implement your own hosting management interfaces.
For purposes of discovery, the management interfaces fall into two broad categories:
Management interfaces that the host implements and the runtime discovers through the IHostControl interface.
Management interfaces that the CLR provides and the host discovers through the ICLRControl interface.
The following table groups the interfaces by the kind of functionality they provide. The most important interface within each group is listed first.
Group |
Function |
Interfaces |
|---|---|---|
Assembly loading management |
Enables the host to customize the locations from which assemblies are loaded, the way versions are managed, and the formats from which assemblies can be loaded. For example, assemblies could be loaded from a database instead of from files on the hard disk. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
Policy management |
Enables the host to specify the way program failures are handled, to support different reliability requirements. The host uses the ICLRControl interface to gain access to the runtime manager, and implements IHostPolicyManager callbacks for failure notifications from the runtime. |
|
Host protection management |
Enables the host to enforce its own programming model, by preventing the use of specified types or members. For example, the host can disallow the use of threading or synchronization primitives. The host uses the ICLRControl interface to gain access to the runtime manager. |
|
Memory management |
Enables the host to control memory allocation by providing replacements for the operating system functions that the CLR uses to allocate memory. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
Garbage collection management |
Enables the host to implement methods to receive notification of the beginning and end of garbage collection. Enables the host to initiate collections, to collect statistics, and to specify some characteristics of collection. The host uses the ICLRControl interface to gain access to the runtime manager. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
Debug management |
Enables the host to discover whether a debugger is attached, to provide additional debugging information, and to customize debugging tasks. The host uses the ICLRControl interface to gain access to the runtime manager. |
|
CLR event management |
Enables a host to register for notification of the events enumerated by EClrEvent. The host uses the ICLRControl interface to gain access to the runtime manager, and implements its event handlers by using the IActionOnCLREvent interface. |
|
Task management |
Enables the host to be notified whenever a thread makes a transition between managed and unmanaged code. Enables the host to control thread affinity, when tasks are started and stopped, and how they are scheduled. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
Thread pool management |
Enables the host to implement its own thread pool for the runtime to use. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
Synchronization management |
Enables the host to implement its own synchronization primitives for the runtime to use. The host can provide events, critical sections, and semaphores. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
|
I/O completion management |
Enables the host to implement its own implementation of asynchronous input/output. The CLR uses the IHostControl interface to discover whether a host implements this group of interfaces. |
.gif "Note") Note |
|---|
The hosting interfaces for earlier versions of the runtime are documented in .NET Framework 1.0 and 1.1 Hosting Interfaces. |
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.NET Framework 4 Hosting Management Interfaces
The .NET Framework 4 consolidates the 2.0 hosting API within the following interfaces:
ICLRMetaHost provides methods that return a specific version of the CLR, list all installed CLRs, list all in-process runtimes, return the activation interface, and discover the CLR version used to compile an assembly.
ICLRMetaHostPolicy supplies the GetRequestedRuntime method that provides a CLR interface based on a policy criteria, managed assembly, version and configuration file.
ICLRRuntimeInfo provides methods that return information about a specific runtime, including version, directory, and load status.
ICLRStrongName groups all CLR version 2.0 strong naming global static functions that are exported by MSCorEE.dll (except StrongNameErrorInfo) into a single interface. All ICLRStrongName methods return standard COM HRESULTS.
These interfaces encapsulate and supersede the .NET Framework 2.0 hosting interfaces.
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Application Domain Managers
For programs that host the common language runtime, application domains provide greater reliability by isolating assemblies from one another. Assemblies can be unloaded from the process by unloading application domains.
To manage multiple application domains, the .NET Framework provides the AppDomainManager class as a base class from which you can derive your own application domain managers. The application domain manager you design for your host application is essentially an extension of the host, in managed code. It is automatically loaded into each application domain created in your process.
The application domain manager can improve performance by eliminating some transitions between managed and unmanaged code. It can receive notification of the creation of new application domains, and give you an opportunity to configure them. The application domain manager also provides a way for an unmanaged host to call managed code.
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Related Topics
Title |
Description |
|---|---|
Describes how to load the runtime into a process, initialize it, and set values to specify its behavior. |
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Describes how to unload application domains and shut down a process. |
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Describes how to set a role-based security policy. |
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Describes how to set an application domain-level security policy. |
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Describes how to load and execute user code. |
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Describes how to create and configure application domains in which to run user code. |
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Describes how to determine where to set boundaries for a new application domain. |
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Describes how to make the transition from unmanaged code to execute managed hosting code and user code. |
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Describes how to activate a version of the runtime other than the one specified in the application configuration file. |
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Describes hosts that ship with the .NET Framework. |
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Describes the constructs that hosts use to isolate code running within a process. |
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Describes running multiple versions of an application, a component, or the runtime. |
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Describes the unmanaged interfaces for hosting the runtime in the .NET Framework version 4. |
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Describes the unmanaged interfaces for hosting the runtime in the .NET Framework version 2.0. |
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Reference
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