Task.Wait Method
Definition
Important
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Waits for the Task to complete execution.
Overloads
Wait(TimeSpan, CancellationToken) |
Waits for the Task to complete execution. |
Wait(Int32, CancellationToken) |
Waits for the Task to complete execution. The wait terminates if a timeout interval elapses or a cancellation token is canceled before the task completes. |
Wait(TimeSpan) |
Waits for the Task to complete execution within a specified time interval. |
Wait(CancellationToken) |
Waits for the Task to complete execution. The wait terminates if a cancellation token is canceled before the task completes. |
Wait() |
Waits for the Task to complete execution. |
Wait(Int32) |
Waits for the Task to complete execution within a specified number of milliseconds. |
Wait(TimeSpan, CancellationToken)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution.
public:
bool Wait(TimeSpan timeout, System::Threading::CancellationToken cancellationToken);
public bool Wait (TimeSpan timeout, System.Threading.CancellationToken cancellationToken);
member this.Wait : TimeSpan * System.Threading.CancellationToken -> bool
Public Function Wait (timeout As TimeSpan, cancellationToken As CancellationToken) As Boolean
Parameters
- timeout
- TimeSpan
The time to wait, or InfiniteTimeSpan to wait indefinitely
- cancellationToken
- CancellationToken
A CancellationToken to observe while waiting for the task to complete.
Returns
true
if the Task completed execution within the allotted time; otherwise, false
.
Exceptions
timeout
is a negative number other than -1 milliseconds, which represents an
infinite time-out
-or-
timeout is greater than MaxValue.
The cancellationToken
was canceled.
Applies to
Wait(Int32, CancellationToken)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution. The wait terminates if a timeout interval elapses or a cancellation token is canceled before the task completes.
public:
bool Wait(int millisecondsTimeout, System::Threading::CancellationToken cancellationToken);
public bool Wait (int millisecondsTimeout, System.Threading.CancellationToken cancellationToken);
member this.Wait : int * System.Threading.CancellationToken -> bool
Public Function Wait (millisecondsTimeout As Integer, cancellationToken As CancellationToken) As Boolean
Parameters
- millisecondsTimeout
- Int32
The number of milliseconds to wait, or Infinite (-1) to wait indefinitely.
- cancellationToken
- CancellationToken
A cancellation token to observe while waiting for the task to complete.
Returns
true
if the Task completed execution within the allotted time; otherwise, false
.
Exceptions
The cancellationToken
was canceled.
The Task has been disposed.
millisecondsTimeout
is a negative number other than -1, which represents an infinite time-out.
The task was canceled. The InnerExceptions collection contains a TaskCanceledException object.
-or-
An exception was thrown during the execution of the task. The InnerExceptions collection contains information about the exception or exceptions.
Examples
The following example calls the Wait(Int32, CancellationToken) method to provide both a timeout value and a cancellation token that can end the wait for a task's completion. A new thread is started and executes the CancelToken
method, which pauses and then calls the CancellationTokenSource.Cancel method to cancel the cancellation tokens. A task is then launched and delays for 5 seconds. The Wait method is then called to wait for the task's completion and is provided both a brief timeout value and a cancellation token.
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
CancellationTokenSource ts = new CancellationTokenSource();
Thread thread = new Thread(CancelToken);
thread.Start(ts);
Task t = Task.Run( () => { Task.Delay(5000).Wait();
Console.WriteLine("Task ended delay...");
});
try {
Console.WriteLine("About to wait completion of task {0}", t.Id);
bool result = t.Wait(1510, ts.Token);
Console.WriteLine("Wait completed normally: {0}", result);
Console.WriteLine("The task status: {0:G}", t.Status);
}
catch (OperationCanceledException e) {
Console.WriteLine("{0}: The wait has been canceled. Task status: {1:G}",
e.GetType().Name, t.Status);
Thread.Sleep(4000);
Console.WriteLine("After sleeping, the task status: {0:G}", t.Status);
ts.Dispose();
}
}
private static void CancelToken(Object obj)
{
Thread.Sleep(1500);
Console.WriteLine("Canceling the cancellation token from thread {0}...",
Thread.CurrentThread.ManagedThreadId);
CancellationTokenSource source = obj as CancellationTokenSource;
if (source != null) source.Cancel();
}
}
// The example displays output like the following if the wait is canceled by
// the cancellation token:
// About to wait completion of task 1
// Canceling the cancellation token from thread 3...
// OperationCanceledException: The wait has been canceled. Task status: Running
// Task ended delay...
// After sleeping, the task status: RanToCompletion
// The example displays output like the following if the wait is canceled by
// the timeout interval expiring:
// About to wait completion of task 1
// Wait completed normally: False
// The task status: Running
// Canceling the cancellation token from thread 3...
open System
open System.Threading
open System.Threading.Tasks
let cancelToken (obj: obj) =
Thread.Sleep 1500
printfn $"Canceling the cancellation token from thread {Thread.CurrentThread.ManagedThreadId}..."
match obj with
| :? CancellationTokenSource as source -> source.Cancel()
| _ -> ()
let ts = new CancellationTokenSource()
let thread = Thread(ParameterizedThreadStart cancelToken)
thread.Start ts
let t =
Task.Run(fun () ->
Task.Delay(5000).Wait()
printfn "Task ended delay...")
try
printfn $"About to wait completion of task {t.Id}"
let result = t.Wait(1510, ts.Token)
printfn $"Wait completed normally: {result}"
printfn $"The task status: {t.Status:G}"
with :? OperationCanceledException as e ->
printfn $"{e.GetType().Name}: The wait has been canceled. Task status: {t.Status:G}"
Thread.Sleep 4000
printfn $"After sleeping, the task status: {t.Status:G}"
ts.Dispose()
// The example displays output like the following if the wait is canceled by
// the cancellation token:
// About to wait completion of task 1
// Canceling the cancellation token from thread 3...
// OperationCanceledException: The wait has been canceled. Task status: Running
// Task ended delay...
// After sleeping, the task status: RanToCompletion
// The example displays output like the following if the wait is canceled by
// the timeout interval expiring:
// About to wait completion of task 1
// Wait completed normally: False
// The task status: Running
// Canceling the cancellation token from thread 3...
Imports System.Threading
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim ts As New CancellationTokenSource()
Dim thread As New Thread(AddressOf CancelToken)
thread.Start(ts)
Dim t As Task = Task.Run( Sub()
Task.Delay(5000).Wait()
Console.WriteLine("Task ended delay...")
End Sub)
Try
Console.WriteLine("About to wait completion of task {0}", t.Id)
Dim result As Boolean = t.Wait(1510, ts.Token)
Console.WriteLine("Wait completed normally: {0}", result)
Console.WriteLine("The task status: {0:G}", t.Status)
Catch e As OperationCanceledException
Console.WriteLine("{0}: The wait has been canceled. Task status: {1:G}",
e.GetType().Name, t.Status)
Thread.Sleep(4000)
Console.WriteLine("After sleeping, the task status: {0:G}", t.Status)
ts.Dispose()
End Try
End Sub
Private Sub CancelToken(obj As Object)
Thread.Sleep(1500)
Console.WriteLine("Canceling the cancellation token from thread {0}...",
Thread.CurrentThread.ManagedThreadId)
If TypeOf obj Is CancellationTokenSource Then
Dim source As CancellationTokenSource = CType(obj, CancellationTokenSource)
source.Cancel()
End If
End Sub
End Module
' The example displays output like the following if the wait is canceled by
' the cancellation token:
' About to wait completion of task 1
' Canceling the cancellation token from thread 3...
' OperationCanceledException: The wait has been canceled. Task status: Running
' Task ended delay...
' After sleeping, the task status: RanToCompletion
' The example displays output like the following if the wait is canceled by
' the timeout interval expiring:
' About to wait completion of task 1
' Wait completed normally: False
' The task status: Running
' Canceling the cancellation token from thread 3...
Note that the precise output from the example depends on whether the wait was canceled because of the cancellation token or because the timeout interval elapsed.
Remarks
Wait(Int32, CancellationToken) is a synchronization method that causes the calling thread to wait for the current task instance to complete until one of the following occurs:
The task completes successfully.
The task itself is canceled or throws an exception. In this case, you handle an AggregateException exception. The AggregateException.InnerExceptions property contains details about the exception or exceptions.
The
cancellationToken
cancellation token is canceled. In this case, the call to the Wait(Int32, CancellationToken) method throws an OperationCanceledException.The interval defined by
millisecondsTimeout
elapses. In this case, the current thread resumes execution and the method returnsfalse
.
Note
Canceling the cancellationToken
cancellation token has no effect on the running task unless it has also been passed the cancellation token and is prepared to handle cancellation. Passing the cancellationToken
object to this method simply allows the wait to be canceled based on some condition.
Applies to
Wait(TimeSpan)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution within a specified time interval.
public:
bool Wait(TimeSpan timeout);
public bool Wait (TimeSpan timeout);
member this.Wait : TimeSpan -> bool
Public Function Wait (timeout As TimeSpan) As Boolean
Parameters
- timeout
- TimeSpan
A TimeSpan that represents the number of milliseconds to wait, or a TimeSpan that represents -1 milliseconds to wait indefinitely.
Returns
true
if the Task completed execution within the allotted time; otherwise, false
.
Exceptions
The Task has been disposed.
timeout
is a negative number other than -1 milliseconds, which represents an infinite time-out.
-or-
timeout
is greater than Int32.MaxValue.
The task was canceled. The InnerExceptions collection contains a TaskCanceledException object.
-or-
An exception was thrown during the execution of the task. The InnerExceptions collection contains information about the exception or exceptions.
Examples
The following example starts a task that generates five million random integers between 0 and 100 and computes their mean. The example uses the Wait(TimeSpan) method to wait for the application to complete within 150 milliseconds. If the application completes normally, the task displays the sum and mean of the random numbers that it has generated. If the timeout interval has elapsed, the example displays a message before it terminates.
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
Task t = Task.Run( () => {
Random rnd = new Random();
long sum = 0;
int n = 5000000;
for (int ctr = 1; ctr <= n; ctr++) {
int number = rnd.Next(0, 101);
sum += number;
}
Console.WriteLine("Total: {0:N0}", sum);
Console.WriteLine("Mean: {0:N2}", sum/n);
Console.WriteLine("N: {0:N0}", n);
} );
TimeSpan ts = TimeSpan.FromMilliseconds(150);
if (! t.Wait(ts))
Console.WriteLine("The timeout interval elapsed.");
}
}
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
// Or it displays the following output:
// The timeout interval elapsed.
open System
open System.Threading.Tasks
let t =
Task.Run(fun () ->
let rnd = Random()
let mutable sum = 0L
let n = 5000000
for _ = 1 to n do
let number = rnd.Next(0, 101)
sum <- sum + int64 number
printfn $"Total: {sum:N0}"
printfn $"Mean: {float sum / float n:N2}"
printfn $"N: {n:N0}")
let ts = TimeSpan.FromMilliseconds 150
if t.Wait ts |> not then
printfn "The timeout interval elapsed."
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
// Or it displays the following output:
// The timeout interval elapsed.
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim t As Task = Task.Run( Sub()
Dim rnd As New Random()
Dim sum As Long
Dim n As Integer = 5000000
For ctr As Integer = 1 To n
Dim number As Integer = rnd.Next(0, 101)
sum += number
Next
Console.WriteLine("Total: {0:N0}", sum)
Console.WriteLine("Mean: {0:N2}", sum/n)
Console.WriteLine("N: {0:N0}", n)
End Sub)
Dim ts As TimeSpan = TimeSpan.FromMilliseconds(150)
If Not t.Wait(ts) Then
Console.WriteLine("The timeout interval elapsed.")
End If
End Sub
End Module
' The example displays output similar to the following:
' Total: 50,015,714
' Mean: 50.02
' N: 1,000,000
' Or it displays the following output:
' The timeout interval elapsed.
Remarks
Wait(TimeSpan) is a synchronization method that causes the calling thread to wait for the current task instance to complete until one of the following occurs:
The task completes successfully.
The task itself is canceled or throws an exception. In this case, you handle an AggregateException exception. The AggregateException.InnerExceptions property contains details about the exception or exceptions.
The interval defined by
timeout
elapses. In this case, the current thread resumes execution and the method returnsfalse
.
Applies to
Wait(CancellationToken)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution. The wait terminates if a cancellation token is canceled before the task completes.
public:
void Wait(System::Threading::CancellationToken cancellationToken);
public void Wait (System.Threading.CancellationToken cancellationToken);
member this.Wait : System.Threading.CancellationToken -> unit
Public Sub Wait (cancellationToken As CancellationToken)
Parameters
- cancellationToken
- CancellationToken
A cancellation token to observe while waiting for the task to complete.
Exceptions
The cancellationToken
was canceled.
The task has been disposed.
The task was canceled. The InnerExceptions collection contains a TaskCanceledException object.
-or-
An exception was thrown during the execution of the task. The InnerExceptions collection contains information about the exception or exceptions.
Examples
The following example illustrates the simple use of a cancellation token to cancel waiting for a task's completion. A task is launched, calls the CancellationTokenSource.Cancel method to cancel any of the token source's cancellation tokens, and then delays for five seconds. Note that the task itself has not been passed the cancellation token and is not cancelable. The application thread calls the task's Task.Wait method to wait for the task to complete, but the wait is canceled once the cancellation token is cancelled and an OperationCanceledException is thrown. The exception handler reports the exception and then sleeps for six seconds. As the output from the example shows, that delay allows the task to complete in the RanToCompletion state.
using System;
using System.Threading;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
CancellationTokenSource ts = new CancellationTokenSource();
Task t = Task.Run( () => { Console.WriteLine("Calling Cancel...");
ts.Cancel();
Task.Delay(5000).Wait();
Console.WriteLine("Task ended delay...");
});
try {
Console.WriteLine("About to wait for the task to complete...");
t.Wait(ts.Token);
}
catch (OperationCanceledException e) {
Console.WriteLine("{0}: The wait has been canceled. Task status: {1:G}",
e.GetType().Name, t.Status);
Thread.Sleep(6000);
Console.WriteLine("After sleeping, the task status: {0:G}", t.Status);
}
ts.Dispose();
}
}
// The example displays output like the following:
// About to wait for the task to complete...
// Calling Cancel...
// OperationCanceledException: The wait has been canceled. Task status: Running
// Task ended delay...
// After sleeping, the task status: RanToCompletion
open System
open System.Threading
open System.Threading.Tasks
let ts = new CancellationTokenSource()
let t =
Task.Run(fun () ->
printfn "Calling Cancel..."
ts.Cancel()
Task.Delay(5000).Wait()
printfn $"Task ended delay...")
try
printfn "About to wait for the task to complete..."
t.Wait ts.Token
with :? OperationCanceledException as e ->
printfn $"{e.GetType().Name}: The wait has been canceled. Task status: {t.Status:G}"
Thread.Sleep 6000
printfn $"After sleeping, the task status: {t.Status:G}"
ts.Dispose()
// The example displays output like the following:
// About to wait for the task to complete...
// Calling Cancel...
// OperationCanceledException: The wait has been canceled. Task status: Running
// Task ended delay...
// After sleeping, the task status: RanToCompletion
Imports System.Threading
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim ts As New CancellationTokenSource()
Dim t = Task.Run( Sub()
Console.WriteLine("Calling Cancel...")
ts.Cancel()
Task.Delay(5000).Wait()
Console.WriteLine("Task ended delay...")
End Sub)
Try
Console.WriteLine("About to wait for the task to complete...")
t.Wait(ts.Token)
Catch e As OperationCanceledException
Console.WriteLine("{0}: The wait has been canceled. Task status: {1:G}",
e.GetType().Name, t.Status)
Thread.Sleep(6000)
Console.WriteLine("After sleeping, the task status: {0:G}", t.Status)
End Try
ts.Dispose()
End Sub
End Module
' The example displays output like the following:
' About to wait for the task to complete...
' Calling Cancel...
' OperationCanceledException: The wait has been canceled. Task status: Running
' Task ended delay...
' After sleeping, the task status: RanToCompletion
Remarks
The Wait(CancellationToken) method creates a cancelable wait; that is, it causes the current thread to wait until one of the following occurs:
The task completes.
The cancellation token is canceled. In this case, the call to the Wait(CancellationToken) method throws an OperationCanceledException.
Note
Canceling the cancellationToken
cancellation token has no effect on the running task unless it has also been passed the cancellation token and is prepared to handle cancellation. Passing the cancellationToken
object to this method simply allows the wait to be canceled.
Applies to
Wait()
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution.
public:
void Wait();
public void Wait ();
member this.Wait : unit -> unit
Public Sub Wait ()
Exceptions
The Task has been disposed.
The task was canceled. The InnerExceptions collection contains a TaskCanceledException object.
-or-
An exception was thrown during the execution of the task. The InnerExceptions collection contains information about the exception or exceptions.
Examples
The following example starts a task that generates one million random integers between 0 and 100 and computes their mean. The example uses the Wait method to ensure that the task completes before the application terminates. Otherwise, because this is a console application, the example would terminate before the task can compute and display the mean.
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
Task t = Task.Run( () => {
Random rnd = new Random();
long sum = 0;
int n = 1000000;
for (int ctr = 1; ctr <= n; ctr++) {
int number = rnd.Next(0, 101);
sum += number;
}
Console.WriteLine("Total: {0:N0}", sum);
Console.WriteLine("Mean: {0:N2}", sum/n);
Console.WriteLine("N: {0:N0}", n);
} );
t.Wait();
}
}
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
open System
open System.Threading.Tasks
let t =
Task.Run(fun () ->
let rnd = Random()
let mutable sum = 0L
let n = 1000000
for _ = 1 to n do
let number = rnd.Next(0, 101)
sum <- sum + int64 number
printfn $"Total: {sum:N0}"
printfn $"Mean: {float sum / float n:N2}"
printfn $"N: {n:N0}")
t.Wait()
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim t As Task = Task.Run( Sub()
Dim rnd As New Random()
Dim sum As Long
Dim n As Integer = 1000000
For ctr As Integer = 1 To n
Dim number As Integer = rnd.Next(0, 101)
sum += number
Next
Console.WriteLine("Total: {0:N0}", sum)
Console.WriteLine("Mean: {0:N2}", sum/n)
Console.WriteLine("N: {0:N0}", n)
End Sub)
t.Wait()
End Sub
End Module
' The example displays output similar to the following:
' Total: 50,015,714
' Mean: 50.02
' N: 1,000,000
Remarks
Wait is a synchronization method that causes the calling thread to wait until the current task has completed. If the current task has not started execution, the Wait method attempts to remove the task from the scheduler and execute it inline on the current thread. If it is unable to do that, or if the current task has already started execution, it blocks the calling thread until the task completes. For more information, see Task.Wait and "Inlining" in the Parallel Programming with .NET blog.
See also
Applies to
Wait(Int32)
- Source:
- Task.cs
- Source:
- Task.cs
- Source:
- Task.cs
Waits for the Task to complete execution within a specified number of milliseconds.
public:
bool Wait(int millisecondsTimeout);
public bool Wait (int millisecondsTimeout);
member this.Wait : int -> bool
Public Function Wait (millisecondsTimeout As Integer) As Boolean
Parameters
- millisecondsTimeout
- Int32
The number of milliseconds to wait, or Infinite (-1) to wait indefinitely.
Returns
true
if the Task completed execution within the allotted time; otherwise, false
.
Exceptions
The Task has been disposed.
millisecondsTimeout
is a negative number other than -1, which represents an infinite time-out.
The task was canceled. The InnerExceptions collection contains a TaskCanceledException object.
-or-
An exception was thrown during the execution of the task. The InnerExceptions collection contains information about the exception or exceptions.
Examples
The following example starts a task that generates five million random integers between 0 and 100 and computes their mean. The example uses the Wait(Int32) method to wait for the application to complete within 150 milliseconds. If the application completes normally, the task displays the sum and mean of the random numbers that it has generated. If the timeout interval has elapsed, the example displays a message before it terminates.
using System;
using System.Threading.Tasks;
public class Example
{
public static void Main()
{
Task t = Task.Run( () => {
Random rnd = new Random();
long sum = 0;
int n = 5000000;
for (int ctr = 1; ctr <= n; ctr++) {
int number = rnd.Next(0, 101);
sum += number;
}
Console.WriteLine("Total: {0:N0}", sum);
Console.WriteLine("Mean: {0:N2}", sum/n);
Console.WriteLine("N: {0:N0}", n);
} );
if (! t.Wait(150))
Console.WriteLine("The timeout interval elapsed.");
}
}
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
// Or it displays the following output:
// The timeout interval elapsed.
open System
open System.Threading.Tasks
let t =
Task.Run(fun () ->
let rnd = Random()
let mutable sum = 0L
let n = 5000000
for _ = 1 to n do
let number = rnd.Next(0, 101)
sum <- sum + int64 number
printfn $"Total: {sum:N0}"
printfn $"Mean: {float sum / float n:N2}"
printfn $"N: {n:N0}")
if t.Wait 150 |> not then
printfn "The timeout interval elapsed."
// The example displays output similar to the following:
// Total: 50,015,714
// Mean: 50.02
// N: 1,000,000
// Or it displays the following output:
// The timeout interval elapsed.
Imports System.Threading.Tasks
Module Example
Public Sub Main()
Dim t As Task = Task.Run( Sub()
Dim rnd As New Random()
Dim sum As Long
Dim n As Integer = 5000000
For ctr As Integer = 1 To n
Dim number As Integer = rnd.Next(0, 101)
sum += number
Next
Console.WriteLine("Total: {0:N0}", sum)
Console.WriteLine("Mean: {0:N2}", sum/n)
Console.WriteLine("N: {0:N0}", n)
End Sub)
If Not t.Wait(150) Then
Console.WriteLine("The timeout interval elapsed.")
End If
End Sub
End Module
' The example displays output similar to the following:
' Total: 50,015,714
' Mean: 50.02
' N: 1,000,000
' Or it displays the following output:
' The timeout interval elapsed.
Remarks
Wait(Int32) is a synchronization method that causes the calling thread to wait for the current task instance to complete until one of the following occurs:
The task completes successfully.
The task itself is canceled or throws an exception. In this case, you handle an AggregateException exception. The AggregateException.InnerExceptions property contains details about the exception or exceptions.
The interval defined by
millisecondsTimeout
elapses. In this case, the current thread resumes execution and the method returnsfalse
.