ThreadHelper Class

Article
04/29/2015

Provides a generic dispatcher helper to ensure that a method is invoked on the application's main thread.

Inheritance Hierarchy

Object
Microsoft.VisualStudio.Shell.ThreadHelper

Namespace: Microsoft.VisualStudio.Shell
Assembly: Microsoft.VisualStudio.Shell.12.0 (in Microsoft.VisualStudio.Shell.12.0.dll)

Syntax

'Declaration
Public MustInherit Class ThreadHelper

public abstract class ThreadHelper

public ref class ThreadHelper abstract

[<AbstractClass>]
type ThreadHelper =  class end

public abstract class ThreadHelper

The ThreadHelper type exposes the following members.

Constructors

	Name	Description
	ThreadHelper	Initializes a new instance of ThreadHelper.

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Properties

	Name	Description
	Generic	Gets a generic ThreadHelper.
	JoinableTaskContext	Gets the singleton JoinableTaskContext instance for Visual Studio.
	JoinableTaskFactory	Gets the joinable task factory for Visual Studio.

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Methods

	Name	Description
	BeginInvoke(Action)	Schedules an action for execution on the UI thread asynchronously.
	BeginInvoke(DispatcherPriority, Action)	Schedules an action for execution on the UI thread asynchronously.
	CheckAccess	Determines whether the call is being made on the UI thread.
	Equals	Determines whether the specified object is equal to the current object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as the default hash function. (Inherited from Object.)
	GetInvocationWrapper	Gets the invocation wrapper.
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	Invoke(Action)	Calls an action on the UI thread, re-entering (if necessary) any code already executing on the UI thread.
	Invoke<TResult>(Func<TResult>)
	InvokeAsync
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ThrowIfNotOnUIThread	Determines whether the call is being made on the UI thread, and throws COMException(RPC_E_WRONG_THREAD) if it is not.
	ThrowIfOnUIThread	Determines whether the call is being made on the UI thread ,and throws COMException(RPC_E_WRONG_THREAD) if it is.
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Remarks

We use the current application's dispatcher for convenient identification of the main thread. Note that this means that the application object must be initialized by the window manager.

However, DispatcherOperation objects are not used, because they are not compatible with RPC. For example, if the UI thread is in the middle of an RPC call, and code must run on the UI thread, then DispatcherOperation objects will not get through. This is because DispatcherOperation objects are initiated by posting a message to the UI thread, and the UI thread must dispatch that message. If the UI thread is making an RPC call, these messages will not be removed from the queue. The standard OLE message filter processes only a limited set of messages from the queue.

By going through a private service, the operation becomes a COM call on the UI thread. This operation is allowed through the Visual Studio message filter if it is part of the same logical call, since the message filter will see it as a nested call and may not reject it.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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