How to cancel a Parallel.For and Parallel.Foreach loop – Task Parallel Library

In my previous article, I explained about Parallel.For and Parallel.Foreach loop in detail. In this article I will explain, how to cancel running or ongoing Parallel.For and Parallel.Foreach loop on certain event.

Parallel.For and Parallel.Foreach has overload methods to pass ParallelOptions to accept cancel request from user. We need to set CancelationToken to ParallelOptions and pass it to Parallel.For and Parallel.Foreach methods. When user request for cancelling parallel loop via cancellation token, then the parallel loop will throw an OperationCanceledException and cancel the parallel loop. See below example for more information.

Code –

	using System.Collections.Generic;
	using System.Diagnostics;
	using System.Linq;
	using System.Text;
	using System;
	using System.Threading.Tasks;
	using System.Threading;
	namespace ParallelFor
	{
	class Program
	{
	static void Main(string[] args)
	{
	using (CancellationTokenSource cancelToken = new CancellationTokenSource())
	{
	//Setting cancellationtoken to parallel options
	ParallelOptions options = new ParallelOptions();
	options.CancellationToken = cancelToken.Token;
	Console.WriteLine("Press 'c' to cancel.");
	//running another thread to get user cancel request
	Task.Factory.StartNew(() =>
	{
	if (Console.ReadKey().KeyChar == 'c')
	cancelToken.Cancel();
	});
	try
	{
	Console.Write("Starting Parallel.For loop");
	Parallel.For(0, 100000, options, (i) =>
	{
	Console.Write("{0}, ", i);
	options.CancellationToken.ThrowIfCancellationRequested();
	});
	}
	catch (OperationCanceledException ex)
	{
	Console.ForegroundColor = ConsoleColor.Red;
	Console.WriteLine("Parallel loop has been canceled by user");
	}
	catch (Exception e)
	{
	throw (e);
	}
	}
	Console.ReadLine();
	}
	}
	}

view raw Program.cs hosted with ❤ by GitHub

Output –

As you can see in above example, when user request for cancel the parallel loop, cancellation token of parallel options will throw an OperationCanceledException and cancel the running parallel loop.

References –

MSDN

See also –

Parallel.For and Parallel.Foreach – TPL
How to handle exception in Parallel.For and Parallel.Foreach loop? – TPL