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11/18/2011

Task Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents an asynchronous operation.

Inheritance Hierarchy

System.Object
System.Threading.Tasks.Task
System.Threading.Tasks.Task<TResult>

Namespace: System.Threading.Tasks
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<DebuggerDisplayAttribute("Id = {Id}, Status = {Status}, Method = {DebuggerDisplayMethodDescription}")> _
Public Class Task _
    Implements IAsyncResult, IDisposable

[DebuggerDisplayAttribute("Id = {Id}, Status = {Status}, Method = {DebuggerDisplayMethodDescription}")]
public class Task : IAsyncResult, IDisposable

The Task type exposes the following members.

Constructors

	Name	Description
	Task(Action)	Initializes a new Task with the specified action.
	Task(Action, CancellationToken)	Initializes a new Task with the specified action and CancellationToken.
	Task(Action, TaskCreationOptions)	Initializes a new Task with the specified action and creation options.
	Task(Action<Object>, Object)	Initializes a new Task with the specified action and state.
	Task(Action, CancellationToken, TaskCreationOptions)	Initializes a new Task with the specified action and creation options.
	Task(Action<Object>, Object, CancellationToken)	Initializes a new Task with the specified action, state, and options.
	Task(Action<Object>, Object, TaskCreationOptions)	Initializes a new Task with the specified action, state, and options.
	Task(Action<Object>, Object, CancellationToken, TaskCreationOptions)	Initializes a new Task with the specified action, state, and options.

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Properties

	Name	Description
	AsyncState	Gets the state object supplied when the Task was created, or null if none was supplied.
	CreationOptions	Gets the TaskCreationOptions used to create this task.
	CurrentId	Returns the unique ID of the currently executing Task.
	Exception	Gets the AggregateException that caused the Task to end prematurely. If the Task completed successfully or has not yet thrown any exceptions, this will return null.
	Factory	Provides access to factory methods for creating Task and Task<TResult> instances.
	Id	Gets a unique ID for this Task instance.
	IsCanceled	Gets whether this Task instance has completed execution due to being canceled.
	IsCompleted	Gets whether this Task has completed.
	IsFaulted	Gets whether the Task completed due to an unhandled exception.
	Status	Gets the TaskStatus of this Task.

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Methods

	Name	Description
	ContinueWith(Action<Task>)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith(Action<Task>, CancellationToken)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith(Action<Task>, TaskContinuationOptions)	Creates a continuation that executes according to the specified TaskContinuationOptions.
	ContinueWith(Action<Task>, TaskScheduler)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith(Action<Task>, CancellationToken, TaskContinuationOptions, TaskScheduler)	Creates a continuation that executes according to the specified TaskContinuationOptions.
	ContinueWith<TResult>(Func<Task, TResult>)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith<TResult>(Func<Task, TResult>, CancellationToken)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith<TResult>(Func<Task, TResult>, TaskContinuationOptions)	Creates a continuation that executes according to the condition specified in continuationOptions.
	ContinueWith<TResult>(Func<Task, TResult>, TaskScheduler)	Creates a continuation that executes asynchronously when the target Task completes.
	ContinueWith<TResult>(Func<Task, TResult>, CancellationToken, TaskContinuationOptions, TaskScheduler)	Creates a continuation that executes according to the condition specified in continuationOptions.
	Dispose()	Releases all resources used by the current instance of the Task class.
	Dispose(Boolean)	Disposes the Task, releasing all of its unmanaged resources.
	Equals(Object)	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 the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	RunSynchronously()	Runs the Task synchronously on the current TaskScheduler.
	RunSynchronously(TaskScheduler)	Runs the Task synchronously on the TaskScheduler provided.
	Start()	Starts the Task, scheduling it for execution to the current TaskScheduler.
	Start(TaskScheduler)	Starts the Task, scheduling it for execution to the specified TaskScheduler.
	ToString	Returns a string that represents the current object. (Inherited from Object.)
	Wait()	Waits for the Task to complete execution.
	Wait(CancellationToken)	Waits for the Task to complete execution.
	Wait(Int32)	Waits for the Task to complete execution.
	Wait(TimeSpan)	Waits for the Task to complete execution.
	Wait(Int32, CancellationToken)	Waits for the Task to complete execution.
	WaitAll(array<Task[])	Waits for all of the provided Task objects to complete execution.
	WaitAll(array<Task[], Int32)	Waits for all of the provided Task objects to complete execution.
	WaitAll(array<Task[], CancellationToken)	Waits for all of the provided Task objects to complete execution.
	WaitAll(array<Task[], TimeSpan)	Waits for all of the provided Task objects to complete execution.
	WaitAll(array<Task[], Int32, CancellationToken)	Waits for all of the provided Task objects to complete execution.
	WaitAny(array<Task[])	Waits for any of the provided Task objects to complete execution.
	WaitAny(array<Task[], Int32)	Waits for any of the provided Task objects to complete execution.
	WaitAny(array<Task[], CancellationToken)	Waits for any of the provided Task objects to complete execution.
	WaitAny(array<Task[], TimeSpan)	Waits for any of the provided Task objects to complete execution.
	WaitAny(array<Task[], Int32, CancellationToken)	Waits for any of the provided Task objects to complete execution.

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Explicit Interface Implementations

	Name	Description
	IAsyncResult.AsyncWaitHandle	Gets a WaitHandle that can be used to wait for the task to complete.
	IAsyncResult.CompletedSynchronously	Gets an indication of whether the operation completed synchronously.

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Remarks

Task instances may be created in a variety of ways. The most common approach is by using the Task type's Factory property to retrieve a TaskFactory instance that can be used to create tasks for several purposes. For example, to create a Task that runs an action, the factory's StartNew method may be used:

// C#
var t = Task.Factory.StartNew(() => DoAction());

' Visual Basic
 Dim t = Task.Factory.StartNew(Function() DoAction())

For more complete examples, see Task Parallelism (Task Parallel Library).

The Task class also provides constructors that initialize the Task but that do not schedule it for execution. For performance reasons, TaskFactory's StartNew method should be the preferred mechanism for creating and scheduling computational tasks, but for scenarios where creation and scheduling must be separated, the constructors may be used, and the task's Start method may then be used to schedule the task for execution at a later time.

For operations that return values, the Task<TResult> class should be used.

For Debugger Developers

For developers implementing custom debuggers, several internal and private members of Task may be useful (these may change from release to release). The Int32 m_taskId field serves as the backing store for the Id property, however accessing this field directly from a debugger may be more efficient than accessing the same value through the property's getter method (the s_taskIdCounter Int32 counter is used to retrieve the next available ID for a Task). Similarly, the Int32 m_stateFlags field stores information about the current lifecycle stage of the Task, information also accessible through the Status property. The m_action System.Object field stores a reference to the Task's delegate, and the m_stateObject System.Object field stores the async state passed to the Task by the developer. Finally, for debuggers that parse stack frames, the InternalWait method serves a potential marker for when a Task is entering a wait operation.

Examples

The following example shows how to start a task by using the StartNew() method:

Version Information

Silverlight

Supported in: 5

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

All members of Task, except for Dispose, are thread-safe and may be used from multiple threads concurrently.

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