Task.WaitAll Method

Definition

Waits for all of the provided Task objects to complete execution.

Overloads

WaitAll(Task[])

Waits for all of the provided Task objects to complete execution.

WaitAll(Task[], Int32)

Waits for all of the provided Task objects to complete execution within a specified number of milliseconds.

WaitAll(Task[], CancellationToken)

Waits for all of the provided Task objects to complete execution unless the wait is cancelled.

WaitAll(Task[], TimeSpan)

Waits for all of the provided cancellable Task objects to complete execution within a specified time interval.

WaitAll(Task[], Int32, CancellationToken)

Waits for all of the provided Task objects to complete execution within a specified number of milliseconds or until the wait is cancelled.

WaitAll(Task[])

Waits for all of the provided Task objects to complete execution.

public static void WaitAll (params System.Threading.Tasks.Task[] tasks);
Parameters
tasks
Task[]

An array of Task instances on which to wait.

Exceptions

One or more of the Task objects in tasks has been disposed.

The tasks argument is null.

The tasks argument contains a null element.

-or-

The tasks argument is an empty array.

At least one of the Task instances was canceled. If a task was canceled, the AggregateException exception contains an OperationCanceledException exception in its InnerExceptions collection.

-or-

An exception was thrown during the execution of at least one of the Task instances.

Examples

The following example starts 10 tasks, each of which is passed an index as a state object. Tasks with an index from two to five throw exceptions. The call to the WaitAll method wraps all exceptions in an AggregateException object and propagates it to the calling thread.

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

class Example
{
    static void Main()
    {
        var tasks = new List<Task<int>>();
         
        // Define a delegate that prints and returns the system tick count
        Func<object, int> action = (object obj) =>
        {
            int i = (int)obj;

            // Make each thread sleep a different time in order to return a different tick count
            Thread.Sleep(i * 100);

            // The tasks that receive an argument between 2 and 5 throw exceptions
            if (2 <= i && i <= 5)
            {
                throw new InvalidOperationException("SIMULATED EXCEPTION");
            }

            int tickCount = Environment.TickCount;
            Console.WriteLine("Task={0}, i={1}, TickCount={2}, Thread={3}", Task.CurrentId, i, tickCount, Thread.CurrentThread.ManagedThreadId);

            return tickCount;
        };

        // Construct started tasks
        for (int i = 0; i < 10; i++)
        {
            int index = i;
            tasks.Add(Task<int>.Factory.StartNew(action, index));
        }

        try
        {
            // Wait for all the tasks to finish.
            Task.WaitAll(tasks.ToArray());

            // We should never get to this point
            Console.WriteLine("WaitAll() has not thrown exceptions. THIS WAS NOT EXPECTED.");
        }
        catch (AggregateException e)
        {
            Console.WriteLine("\nThe following exceptions have been thrown by WaitAll(): (THIS WAS EXPECTED)");
            for (int j = 0; j < e.InnerExceptions.Count; j++)
            {
                Console.WriteLine("\n-------------------------------------------------\n{0}", e.InnerExceptions[j].ToString());
            }
        }
    }
}
// The example displays output like the following:
//     Task=1, i=0, TickCount=1203822250, Thread=3
//     Task=2, i=1, TickCount=1203822359, Thread=4
//     Task=7, i=6, TickCount=1203823484, Thread=3
//     Task=8, i=7, TickCount=1203823890, Thread=4
//     Task=9, i=8, TickCount=1203824296, Thread=3
//     Task=10, i=9, TickCount=1203824796, Thread=4
//     
//     The following exceptions have been thrown by WaitAll(): (THIS WAS EXPECTED)
//     
//     -------------------------------------------------
//     System.InvalidOperationException: SIMULATED EXCEPTION
//        at Example.<Main>b__0(Object obj)
//        at System.Threading.Tasks.Task`1.InnerInvoke()
//        at System.Threading.Tasks.Task.Execute()
//     
//     -------------------------------------------------
//     System.InvalidOperationException: SIMULATED EXCEPTION
//        at Example.<Main>b__0(Object obj)
//        at System.Threading.Tasks.Task`1.InnerInvoke()
//        at System.Threading.Tasks.Task.Execute()
//     
//     -------------------------------------------------
//     System.InvalidOperationException: SIMULATED EXCEPTION
//        at Example.<Main>b__0(Object obj)
//        at System.Threading.Tasks.Task`1.InnerInvoke()
//        at System.Threading.Tasks.Task.Execute()
//     
//     -------------------------------------------------
//     System.InvalidOperationException: SIMULATED EXCEPTION
//        at Example.<Main>b__0(Object obj)
//        at System.Threading.Tasks.Task`1.InnerInvoke()
//        at System.Threading.Tasks.Task.Execute()
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

Module WaitAllDemo
    Sub Main()
        Dim tasks As New List(Of Task(Of Integer))()
        ' Define a delegate that prints and returns the system tick count
        Dim action As Func(Of Object, Integer) = Function(obj As Object)
                                                     Dim i As Integer = CInt(obj)

                                                     ' Make each thread sleep a different time in order to return a different tick count
                                                     Thread.Sleep(i * 100)

                                                     ' The tasks that receive an argument between 2 and 5 throw exceptions
                                                     If 2 <= i AndAlso i <= 5 Then
                                                         Throw New InvalidOperationException("SIMULATED EXCEPTION")
                                                     End If

                                                     Dim tickCount As Integer = Environment.TickCount
                                                     Console.WriteLine("Task={0}, i={1}, TickCount={2}, Thread={3}", Task.CurrentId, i, tickCount, Thread.CurrentThread.ManagedThreadId)

                                                     Return tickCount
                                                 End Function

        ' Construct started tasks
        For i As Integer = 0 To 9
            Dim index As Integer = i
            tasks.Add(Task(Of Integer).Factory.StartNew(action, index))
        Next

        Try
            ' Wait for all the tasks to finish.
            Task.WaitAll(tasks.ToArray())

            ' We should never get to this point
            Console.WriteLine("WaitAll() has not thrown exceptions. THIS WAS NOT EXPECTED.")
        Catch e As AggregateException
            Console.WriteLine(vbLf & "The following exceptions have been thrown by WaitAll(): (THIS WAS EXPECTED)")
            For j As Integer = 0 To e.InnerExceptions.Count - 1
                Console.WriteLine(vbLf & "-------------------------------------------------" & vbLf & "{0}", e.InnerExceptions(j).ToString())
            Next
        End Try
    End Sub
End Module
' The example displays output like the following:
'     Task=1, i=0, TickCount=1203822250, Thread=3
'     Task=2, i=1, TickCount=1203822359, Thread=4
'     Task=7, i=6, TickCount=1203823484, Thread=3
'     Task=8, i=7, TickCount=1203823890, Thread=4
'     Task=9, i=8, TickCount=1203824296, Thread=3
'     Task=10, i=9, TickCount=1203824796, Thread=4
'     
'     The following exceptions have been thrown by WaitAll(): (THIS WAS EXPECTED)
'     
'     -------------------------------------------------
'     System.InvalidOperationException: SIMULATED EXCEPTION
'        at Example.<Main>b__0(Object obj)
'        at System.Threading.Tasks.Task`1.InnerInvoke()
'        at System.Threading.Tasks.Task.Execute()
'     
'     -------------------------------------------------
'     System.InvalidOperationException: SIMULATED EXCEPTION
'        at Example.<Main>b__0(Object obj)
'        at System.Threading.Tasks.Task`1.InnerInvoke()
'        at System.Threading.Tasks.Task.Execute()
'     
'     -------------------------------------------------
'     System.InvalidOperationException: SIMULATED EXCEPTION
'        at Example.<Main>b__0(Object obj)
'        at System.Threading.Tasks.Task`1.InnerInvoke()
'        at System.Threading.Tasks.Task.Execute()
'     
'     -------------------------------------------------
'     System.InvalidOperationException: SIMULATED EXCEPTION
'        at Example.<Main>b__0(Object obj)
'        at System.Threading.Tasks.Task`1.InnerInvoke()
'        at System.Threading.Tasks.Task.Execute()

WaitAll(Task[], Int32)

Waits for all of the provided Task objects to complete execution within a specified number of milliseconds.

public static bool WaitAll (System.Threading.Tasks.Task[] tasks, int millisecondsTimeout);
Parameters
tasks
Task[]

An array of Task instances on which to wait.

millisecondsTimeout
Int32

The number of milliseconds to wait, or Infinite (-1) to wait indefinitely.

Returns

true if all of the Task instances completed execution within the allotted time; otherwise, false.

Exceptions

One or more of the Task objects in tasks has been disposed.

The tasks argument is null.

At least one of the Task instances was canceled. If a task was canceled, the AggregateException contains an OperationCanceledException in its InnerExceptions collection.

-or-

An exception was thrown during the execution of at least one of the Task instances.

millisecondsTimeout is a negative number other than -1, which represents an infinite time-out.

The tasks argument contains a null element.

-or-

The tasks argument is an empty array.

WaitAll(Task[], CancellationToken)

Waits for all of the provided Task objects to complete execution unless the wait is cancelled.

public static void WaitAll (System.Threading.Tasks.Task[] tasks, System.Threading.CancellationToken cancellationToken);
Parameters
tasks
Task[]

An array of Task instances on which to wait.

cancellationToken
CancellationToken

A CancellationToken to observe while waiting for the tasks to complete.

Exceptions

The cancellationToken was canceled.

The tasks argument is null.

At least one of the Task instances was canceled. If a task was canceled, the AggregateException contains an OperationCanceledException in its InnerExceptions collection.

-or-

An exception was thrown during the execution of at least one of the Task instances.

The tasks argument contains a null element.

-or-

The tasks argument is an empty array.

One or more of the Task objects in tasks has been disposed.

Remarks

The cancellationToken argument is used to cancel the wait operation. Cancellation of the tasks is a distinct operation, and is signaled by the AggregateException as noted above.

WaitAll(Task[], TimeSpan)

Waits for all of the provided cancellable Task objects to complete execution within a specified time interval.

public static bool WaitAll (System.Threading.Tasks.Task[] tasks, TimeSpan timeout);
Parameters
tasks
Task[]

An array of Task instances on which to wait.

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 all of the Task instances completed execution within the allotted time; otherwise, false.

Exceptions

One or more of the Task objects in tasks has been disposed.

The tasks argument is null.

At least one of the Task instances was canceled. If a task was canceled, the AggregateException contains an OperationCanceledException in its InnerExceptions collection.

-or-

An exception was thrown during the execution of at least one of the Task instances.

timeout is a negative number other than -1 milliseconds, which represents an infinite time-out.

-or-

timeout is greater than MaxValue.

The tasks argument contains a null element.

-or-

The tasks argument is an empty array.

WaitAll(Task[], Int32, CancellationToken)

Waits for all of the provided Task objects to complete execution within a specified number of milliseconds or until the wait is cancelled.

public static bool WaitAll (System.Threading.Tasks.Task[] tasks, int millisecondsTimeout, System.Threading.CancellationToken cancellationToken);
Parameters
tasks
Task[]

An array of Task instances on which to wait.

millisecondsTimeout
Int32

The number of milliseconds to wait, or Infinite (-1) to wait indefinitely.

cancellationToken
CancellationToken

A CancellationToken to observe while waiting for the tasks to complete.

Returns

true if all of the Task instances completed execution within the allotted time; otherwise, false.

Exceptions

One or more of the Task objects in tasks has been disposed.

The tasks argument is null.

At least one of the Task instances was canceled. If a task was canceled, the AggregateException contains an OperationCanceledException in its InnerExceptions collection.

-or-

An exception was thrown during the execution of at least one of the Task instances.

millisecondsTimeout is a negative number other than -1, which represents an infinite time-out.

The tasks argument contains a null element.

-or-

The tasks argument is an empty array.

The cancellationToken was canceled.

Remarks

The cancellationToken argument is used to cancel the wait operation. Cancellation of the tasks is a distinct operation, and is signaled by the AggregateException noted above.

Applies to