Gör så här: Avbryt en Parallel.For- eller ForEach-loop
Metoderna Parallel.For och Parallel.ForEach stöder annullering med hjälp av annulleringstoken. Mer information om annullering finns i Annullering. I en parallell loop anger CancellationToken du metoden i parametern ParallelOptions och omger sedan det parallella anropet i ett try-catch-block.
Exempel
I följande exempel visas hur du avbryter ett anrop till Parallel.ForEach. Du kan använda samma metod för ett Parallel.For anrop.
namespace CancelParallelLoops
{
using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
class Program
{
static void Main()
{
int[] nums = Enumerable.Range(0, 10_000_000).ToArray();
CancellationTokenSource cts = new();
// Use ParallelOptions instance to store the CancellationToken
ParallelOptions options = new()
{
CancellationToken = cts.Token,
MaxDegreeOfParallelism = Environment.ProcessorCount
};
Console.WriteLine("Press any key to start. Press 'c' to cancel.");
Console.ReadKey();
// Run a task so that we can cancel from another thread.
Task.Factory.StartNew(() =>
{
if (Console.ReadKey().KeyChar is 'c')
cts.Cancel();
Console.WriteLine("press any key to exit");
});
try
{
Parallel.ForEach(nums, options, (num) =>
{
double d = Math.Sqrt(num);
Console.WriteLine("{0} on {1}", d, Environment.CurrentManagedThreadId);
});
}
catch (OperationCanceledException e)
{
Console.WriteLine(e.Message);
}
finally
{
cts.Dispose();
}
Console.ReadKey();
}
}
}
' How to: Cancel a Parallel.For or ForEach Loop
Imports System.Threading
Imports System.Threading.Tasks
Module CancelParallelLoops
Sub Main()
Dim nums() As Integer = Enumerable.Range(0, 10000000).ToArray()
Dim cts As New CancellationTokenSource
' Use ParallelOptions instance to store the CancellationToken
Dim po As New ParallelOptions
po.CancellationToken = cts.Token
po.MaxDegreeOfParallelism = System.Environment.ProcessorCount
Console.WriteLine("Press any key to start. Press 'c' to cancel.")
Console.ReadKey()
' Run a task so that we can cancel from another thread.
Dim t As Task = Task.Factory.StartNew(Sub()
If Console.ReadKey().KeyChar = "c"c Then
cts.Cancel()
End If
Console.WriteLine(vbCrLf & "Press any key to exit.")
End Sub)
Try
' The error "Exception is unhandled by user code" will appear if "Just My Code"
' is enabled. This error is benign. You can press F5 to continue, or disable Just My Code.
Parallel.ForEach(nums, po, Sub(num)
Dim d As Double = Math.Sqrt(num)
Console.CursorLeft = 0
Console.Write("{0:##.##} on {1}", d, Thread.CurrentThread.ManagedThreadId)
End Sub)
Catch e As OperationCanceledException
Console.WriteLine(e.Message)
Finally
cts.Dispose()
End Try
Console.ReadKey()
End Sub
End Module
Om token som signalerar annulleringen är samma token som anges i instansen ParallelOptions , kommer den parallella loopen att utlösa en enda OperationCanceledException vid annullering. Detta hindrar omedelbart alla iterationer från att köras när undantaget genereras. Om någon annan token orsakar annullering, genererar loopen en AggregateException med en OperationCanceledException som .InnerException
