Task Constructors
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Initializes a new Task.
Overloads
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 CancellationToken. |
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. |
Task(Action)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action.
public:
Task(Action ^ action);
public Task (Action action);
new System.Threading.Tasks.Task : Action -> System.Threading.Tasks.Task
Public Sub New (action As Action)
Parameters
- action
- Action
The delegate that represents the code to execute in the task.
Exceptions
The action
argument is null
.
Examples
The following example uses the Task(Action) constructor to create tasks that retrieve the filenames in specified directories. All tasks write the file names to a single ConcurrentBag<T> object. The example then calls the WaitAll(Task[]) method to ensure that all tasks have completed, and then displays a count of the total number of file names written to the ConcurrentBag<T> object.
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Threading.Tasks;
public class Example
{
public static async Task Main()
{
var list = new ConcurrentBag<string>();
string[] dirNames = { ".", ".." };
List<Task> tasks = new List<Task>();
foreach (var dirName in dirNames) {
Task t = new Task( () => { foreach(var path in Directory.GetFiles(dirName))
list.Add(path); } );
tasks.Add(t);
t.Start();
}
await Task.WhenAll(tasks.ToArray());
foreach (Task t in tasks)
Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status);
Console.WriteLine("Number of files read: {0}", list.Count);
}
}
// The example displays output like the following:
// Task 1 Status: RanToCompletion
// Task 2 Status: RanToCompletion
// Number of files read: 23
open System.Collections.Concurrent
open System.IO
open System.Threading.Tasks
let main =
task {
let list = ConcurrentBag<string>()
let dirNames = [ "."; ".." ]
let tasks = ResizeArray()
for dirName in dirNames do
let t =
new Task(fun () ->
for path in Directory.GetFiles dirName do
list.Add path)
tasks.Add t
t.Start()
do! tasks.ToArray() |> Task.WhenAll
for t in tasks do
printfn $"Task {t.Id} Status: {t.Status}"
printfn $"Number of files read: {list.Count}"
}
// The example displays output like the following:
// Task 1 Status: RanToCompletion
// Task 2 Status: RanToCompletion
// Number of files read: 23
Imports System.Collections.Concurrent
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim list As New ConcurrentBag(Of String)()
Dim dirNames() As String = { ".", ".." }
Dim tasks As New List(Of Task)()
For Each dirName In dirNames
Dim t As New Task( Sub()
For Each path In Directory.GetFiles(dirName)
list.Add(path)
Next
End Sub )
tasks.Add(t)
t.Start()
Next
Task.WaitAll(tasks.ToArray())
For Each t In tasks
Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status)
Next
Console.WriteLine("Number of files read: {0}", list.Count)
End Sub
End Module
' The example displays output like the following:
' Task 1 Status: RanToCompletion
' Task 2 Status: RanToCompletion
' Number of files read: 23
The following example is identical, except that it used the Run(Action) method to instantiate and run the task in a single operation. The method returns the Task object that represents the task.
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
var list = new ConcurrentBag<string>();
string[] dirNames = { ".", ".." };
List<Task> tasks = new List<Task>();
foreach (var dirName in dirNames) {
Task t = Task.Run( () => { foreach(var path in Directory.GetFiles(dirName))
list.Add(path); } );
tasks.Add(t);
}
Task.WaitAll(tasks.ToArray());
foreach (Task t in tasks)
Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status);
Console.WriteLine("Number of files read: {0}", list.Count);
}
}
// The example displays output like the following:
// Task 1 Status: RanToCompletion
// Task 2 Status: RanToCompletion
// Number of files read: 23
open System.Collections.Concurrent
open System.IO
open System.Threading.Tasks
let list = ConcurrentBag<string>()
let dirNames = [ "."; ".." ]
let tasks = ResizeArray()
for dirName in dirNames do
let t =
Task.Run(fun () ->
for path in Directory.GetFiles dirName do
list.Add path)
tasks.Add t
tasks.ToArray() |> Task.WaitAll
for t in tasks do
printfn $"Task {t.Id} Status: {t.Status}"
printfn $"Number of files read: {list.Count}"
// The example displays output like the following:
// Task 1 Status: RanToCompletion
// Task 2 Status: RanToCompletion
// Number of files read: 23
Imports System.Collections.Concurrent
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim list As New ConcurrentBag(Of String)()
Dim dirNames() As String = { ".", ".." }
Dim tasks As New List(Of Task)()
For Each dirName In dirNames
Dim t As Task = Task.Run( Sub()
For Each path In Directory.GetFiles(dirName)
list.Add(path)
Next
End Sub )
tasks.Add(t)
Next
Task.WaitAll(tasks.ToArray())
For Each t In tasks
Console.WriteLine("Task {0} Status: {1}", t.Id, t.Status)
Next
Console.WriteLine("Number of files read: {0}", list.Count)
End Sub
End Module
' The example displays output like the following:
' Task 1 Status: RanToCompletion
' Task 2 Status: RanToCompletion
' Number of files read: 23
Remarks
This constructor should only be used in advanced scenarios where it is required that the creation and starting of the task is separated.
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static Task.Run(Action) or TaskFactory.StartNew(Action) method.
If a task with no action is needed just for the consumer of an API to have something to await, a TaskCompletionSource<TResult> should be used.
See also
Applies to
Task(Action, CancellationToken)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action and CancellationToken.
public:
Task(Action ^ action, System::Threading::CancellationToken cancellationToken);
public Task (Action action, System.Threading.CancellationToken cancellationToken);
new System.Threading.Tasks.Task : Action * System.Threading.CancellationToken -> System.Threading.Tasks.Task
Public Sub New (action As Action, cancellationToken As CancellationToken)
Parameters
- action
- Action
The delegate that represents the code to execute in the task.
- cancellationToken
- CancellationToken
The CancellationToken that the new task will observe.
Exceptions
The provided CancellationToken has already been disposed.
The action
argument is null.
Examples
The following example calls the Task(Action, CancellationToken) constructor to create a task that iterates the files in the C:\Windows\System32 directory. The lambda expression calls the Parallel.ForEach method to add information about each file to a List<T> object. Each detached nested task invoked by the Parallel.ForEach loop checks the state of the cancellation token and, if cancellation is requested, calls the CancellationToken.ThrowIfCancellationRequested method. The CancellationToken.ThrowIfCancellationRequested method throws an OperationCanceledException exception that is handled in a catch
block when the calling thread calls the Task.Wait method. The Start method is then called to start the task.
using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static async Task Main()
{
var tokenSource = new CancellationTokenSource();
var token = tokenSource.Token;
var files = new List<Tuple<string, string, long, DateTime>>();
var t = new Task(() => { string dir = "C:\\Windows\\System32\\";
object obj = new Object();
if (Directory.Exists(dir)) {
Parallel.ForEach(Directory.GetFiles(dir),
f => {
if (token.IsCancellationRequested)
token.ThrowIfCancellationRequested();
var fi = new FileInfo(f);
lock(obj) {
files.Add(Tuple.Create(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc));
}
});
}
} , token);
t.Start();
tokenSource.Cancel();
try {
await t;
Console.WriteLine("Retrieved information for {0} files.", files.Count);
}
catch (AggregateException e) {
Console.WriteLine("Exception messages:");
foreach (var ie in e.InnerExceptions)
Console.WriteLine(" {0}: {1}", ie.GetType().Name, ie.Message);
Console.WriteLine("\nTask status: {0}", t.Status);
}
finally {
tokenSource.Dispose();
}
}
}
// The example displays the following output:
// Exception messages:
// TaskCanceledException: A task was canceled.
//
// Task status: Canceled
open System
open System.IO
open System.Threading
open System.Threading.Tasks
let main =
task {
use tokenSource = new CancellationTokenSource()
let token = tokenSource.Token
let files = ResizeArray()
let t =
new Task(
(fun () ->
let dir = @"C:\Windows\System32\"
let obj = obj ()
if Directory.Exists dir then
Parallel.ForEach(
Directory.GetFiles dir,
fun f ->
if token.IsCancellationRequested then
token.ThrowIfCancellationRequested()
let fi = FileInfo f
lock obj (fun () -> files.Add(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc))
)
|> ignore),
token
)
t.Start()
tokenSource.Cancel()
try
do! t
printfn $"Retrieved information for {files.Count} files."
with :? AggregateException as e ->
printfn "Exception messages:"
for ie in e.InnerExceptions do
printfn $" {ie.GetType().Name}: {ie.Message}"
printfn $"Task status: {t.Status}"
}
main.Wait()
// The example displays the following output:
// Exception messages:
// TaskCanceledException: A task was canceled.
//
// Task status: Canceled
Imports System.Collections.Generic
Imports System.IO
Imports System.Threading
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim tokenSource As New CancellationTokenSource()
Dim token As CancellationToken = tokenSource.Token
Dim files As New List(Of Tuple(Of String, String, Long, Date))()
Dim t As New Task(Sub()
Dim dir As String = "C:\Windows\System32\"
Dim obj As New Object()
If Directory.Exists(dir)Then
Parallel.ForEach(Directory.GetFiles(dir),
Sub(f)
If token.IsCancellationRequested Then
token.ThrowIfCancellationRequested()
End If
Dim fi As New FileInfo(f)
SyncLock(obj)
files.Add(Tuple.Create(fi.Name, fi.DirectoryName, fi.Length, fi.LastWriteTimeUtc))
End SyncLock
End Sub)
End If
End Sub, token)
t.Start()
tokenSource.Cancel()
Try
t.Wait()
Console.WriteLine("Retrieved information for {0} files.", files.Count)
Catch e As AggregateException
Console.WriteLine("Exception messages:")
For Each ie As Exception In e.InnerExceptions
Console.WriteLine(" {0}:{1}", ie.GetType().Name, ie.Message)
Next
Console.WriteLine()
Console.WriteLine("Task status: {0}", t.Status)
Finally
tokenSource.Dispose()
End Try
End Sub
End Module
' The example displays the following output:
' Exception messages:
' TaskCanceledException: A task was canceled.
'
' Task status: Canceled
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static Task.Run(Action, CancellationToken) and TaskFactory.StartNew(Action, CancellationToken) methods. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
For more information, see Task Parallelism (Task Parallel Library) and Cancellation in Managed Threads.
Applies to
Task(Action, TaskCreationOptions)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action and creation options.
public:
Task(Action ^ action, System::Threading::Tasks::TaskCreationOptions creationOptions);
public Task (Action action, System.Threading.Tasks.TaskCreationOptions creationOptions);
new System.Threading.Tasks.Task : Action * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task
Public Sub New (action As Action, creationOptions As TaskCreationOptions)
Parameters
- action
- Action
The delegate that represents the code to execute in the task.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The action
argument is null.
The creationOptions
argument specifies an invalid value for TaskCreationOptions.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action, TaskCreationOptions) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
Applies to
Task(Action<Object>, Object)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action and state.
public:
Task(Action<System::Object ^> ^ action, System::Object ^ state);
public Task (Action<object> action, object state);
public Task (Action<object?> action, object? state);
new System.Threading.Tasks.Task : Action<obj> * obj -> System.Threading.Tasks.Task
Public Sub New (action As Action(Of Object), state As Object)
Parameters
- state
- Object
An object representing data to be used by the action.
Exceptions
The action
argument is null.
Examples
The following example defines an array of 6-letter words. Each word is then passed as an argument to the Task(Action<Object>, Object) constructor, whose Action<T> delegate scrambles the characters in the word, then displays the original word and its scrambled version.
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
public class Example
{
public static async Task Main()
{
var tasks = new List<Task>();
Random rnd = new Random();
Object lockObj = new Object();
String[] words6 = { "reason", "editor", "rioter", "rental",
"senior", "regain", "ordain", "rained" };
foreach (var word6 in words6) {
Task t = new Task( (word) => { Char[] chars = word.ToString().ToCharArray();
double[] order = new double[chars.Length];
lock (lockObj) {
for (int ctr = 0; ctr < order.Length; ctr++)
order[ctr] = rnd.NextDouble();
}
Array.Sort(order, chars);
Console.WriteLine("{0} --> {1}", word,
new String(chars));
}, word6);
t.Start();
tasks.Add(t);
}
await Task.WhenAll(tasks.ToArray());
}
}
// The example displays output like the following:
// regain --> irnaeg
// ordain --> rioadn
// reason --> soearn
// rained --> rinade
// rioter --> itrore
// senior --> norise
// rental --> atnerl
// editor --> oteird
open System
open System.Threading.Tasks
let main =
task {
let tasks = ResizeArray()
let rnd = Random()
let lockObj = obj ()
let words6 =
[ "reason"
"editor"
"rioter"
"rental"
"senior"
"regain"
"ordain"
"rained" ]
for word6 in words6 do
let t =
new Task(
(fun word ->
let chars = (string word).ToCharArray()
let order = Array.zeroCreate<double> chars.Length
lock lockObj (fun () ->
for i = 0 to order.Length - 1 do
order[i] <- rnd.NextDouble())
Array.Sort(order, chars)
printfn $"{word} --> {new String(chars)}"),
word6
)
t.Start()
tasks.Add t
do! tasks.ToArray() |> Task.WhenAll
}
main.Wait()
// The example displays output like the following:
// regain --> irnaeg
// ordain --> rioadn
// reason --> soearn
// rained --> rinade
// rioter --> itrore
// senior --> norise
// rental --> atnerl
// editor --> oteird
Imports System.Collections.Generic
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim tasks As New List(Of Task)()
Dim rnd As New Random()
Dim lockObj As New Object()
Dim words6() As String = { "reason", "editor", "rioter", "rental",
"senior", "regain", "ordain", "rained" }
For Each word6 in words6
Dim t As New Task( Sub(word)
Dim chars() As Char = word.ToString().ToCharArray()
Dim order(chars.Length - 1) As Double
SyncLock lockObj
For ctr As Integer = 0 To order.Length - 1
order(ctr) = rnd.NextDouble()
Next
End SyncLock
Array.Sort(order, chars)
Console.WriteLine("{0} --> {1}", word,
New String(chars))
End Sub, word6)
t.Start()
tasks.Add(t)
Next
Task.WaitAll(tasks.ToArray())
End Sub
End Module
' The example displays output like the following:
' regain --> irnaeg
' ordain --> rioadn
' reason --> soearn
' rained --> rinade
' rioter --> itrore
' senior --> norise
' rental --> atnerl
' editor --> oteird
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action<Object>, Object) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
See also
Applies to
Task(Action, CancellationToken, TaskCreationOptions)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action and creation options.
public:
Task(Action ^ action, System::Threading::CancellationToken cancellationToken, System::Threading::Tasks::TaskCreationOptions creationOptions);
public Task (Action action, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);
new System.Threading.Tasks.Task : Action * System.Threading.CancellationToken * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task
Public Sub New (action As Action, cancellationToken As CancellationToken, creationOptions As TaskCreationOptions)
Parameters
- action
- Action
The delegate that represents the code to execute in the task.
- cancellationToken
- CancellationToken
The CancellationToken that the new task will observe.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The CancellationTokenSource that created cancellationToken
has already been disposed.
The action
argument is null.
The creationOptions
argument specifies an invalid value for TaskCreationOptions.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action, CancellationToken, TaskCreationOptions, TaskScheduler) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
For more information, see Task Parallelism (Task Parallel Library) and Task Cancellation.
Applies to
Task(Action<Object>, Object, CancellationToken)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action, state, and CancellationToken.
public:
Task(Action<System::Object ^> ^ action, System::Object ^ state, System::Threading::CancellationToken cancellationToken);
public Task (Action<object> action, object state, System.Threading.CancellationToken cancellationToken);
public Task (Action<object?> action, object? state, System.Threading.CancellationToken cancellationToken);
new System.Threading.Tasks.Task : Action<obj> * obj * System.Threading.CancellationToken -> System.Threading.Tasks.Task
Public Sub New (action As Action(Of Object), state As Object, cancellationToken As CancellationToken)
Parameters
- state
- Object
An object representing data to be used by the action.
- cancellationToken
- CancellationToken
The CancellationToken that the new task will observe.
Exceptions
The CancellationTokenSource that created cancellationToken
has already been disposed.
The action
argument is null.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action<Object>, Object, CancellationToken) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
Applies to
Task(Action<Object>, Object, TaskCreationOptions)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action, state, and options.
public:
Task(Action<System::Object ^> ^ action, System::Object ^ state, System::Threading::Tasks::TaskCreationOptions creationOptions);
public Task (Action<object> action, object state, System.Threading.Tasks.TaskCreationOptions creationOptions);
public Task (Action<object?> action, object? state, System.Threading.Tasks.TaskCreationOptions creationOptions);
new System.Threading.Tasks.Task : Action<obj> * obj * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task
Public Sub New (action As Action(Of Object), state As Object, creationOptions As TaskCreationOptions)
Parameters
- state
- Object
An object representing data to be used by the action.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The action
argument is null.
The creationOptions
argument specifies an invalid value for TaskCreationOptions.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action<Object>, Object, TaskCreationOptions) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.
Applies to
Task(Action<Object>, Object, CancellationToken, TaskCreationOptions)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Initializes a new Task with the specified action, state, and options.
public:
Task(Action<System::Object ^> ^ action, System::Object ^ state, System::Threading::CancellationToken cancellationToken, System::Threading::Tasks::TaskCreationOptions creationOptions);
public Task (Action<object> action, object state, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);
public Task (Action<object?> action, object? state, System.Threading.CancellationToken cancellationToken, System.Threading.Tasks.TaskCreationOptions creationOptions);
new System.Threading.Tasks.Task : Action<obj> * obj * System.Threading.CancellationToken * System.Threading.Tasks.TaskCreationOptions -> System.Threading.Tasks.Task
Public Sub New (action As Action(Of Object), state As Object, cancellationToken As CancellationToken, creationOptions As TaskCreationOptions)
Parameters
- state
- Object
An object representing data to be used by the action.
- cancellationToken
- CancellationToken
The CancellationToken that the new task will observe.
- creationOptions
- TaskCreationOptions
The TaskCreationOptions used to customize the task's behavior.
Exceptions
The CancellationTokenSource that created cancellationToken
has already been disposed.
The action
argument is null.
The creationOptions
argument specifies an invalid value for TaskCreationOptions.
Remarks
Rather than calling this constructor, the most common way to instantiate a Task object and launch a task is by calling the static TaskFactory.StartNew(Action<Object>, Object, CancellationToken, TaskCreationOptions, TaskScheduler) method. The only advantage offered by this constructor is that it allows object instantiation to be separated from task invocation.