CODEWITHSUNDEEP
c#multithreadingtask
P.K.
P.K.

Reputation: 1772

Why second thread with ContinueWith option is not waiting for first thread's end?

Why second thead started by line

var finalTask = parent.ContinueWith( .. )

is not waiting for first thread's end? This is printout proving that the new thread is not waiting for the first one's end:

Starting main thread 1
Starting ContinueWith thread 2
0 0 0
Ending ContinueWith thread 2
ContinueWith thread is finished!
Starting child thread 3
Ends child thread 3
Starting child thread 2
Ends child thread 2
Starting child thread 1
Ends child thread 1

Code:

public static void AttachTasksToMain()
        {
            Task<Int32[]> parent = Task.Run(() =>
            {
                Console.WriteLine("Starting main thread 1");
                var results = new Int32[3];
                new Task(() => {
                    Console.WriteLine("Starting child thread 1");
                    results[0] = 0;
                    Console.WriteLine("Ends child thread 1");
                }, TaskCreationOptions.AttachedToParent).Start();

                new Task(() => {
                    Console.WriteLine("Starting child thread 2");
                    results[1] = 1;
                    Console.WriteLine("Ends child thread 2");
                }, TaskCreationOptions.AttachedToParent).Start();

                new Task(() => {
                    Console.WriteLine("Starting child thread 3");
                    results[2] = 2;
                    Console.WriteLine("Ends child thread 3");
                }, TaskCreationOptions.AttachedToParent).Start();

                //this thread finishes when all child-thread are finished!
                return results;
            });
            //parent.Wait();

            var finalTask = parent.ContinueWith(parentTask =>
            {
                Console.WriteLine("Starting ContinueWith thread 2");
                foreach (int i in parentTask.Result)
                    Console.WriteLine(i);

                Console.WriteLine("Ending ContinueWith thread 2");
            });

            finalTask.Wait();
            Console.WriteLine("ContinueWith thread is finished!");

        }

Upvotes: 2

Views: 171

Answers (1)

Zer0
Zer0

Reputation: 7354

The problem is Task.Run. This starts the task with TaskCreationOptions.DenyChildAttach.

A simple change to using Task.Factory.StartNew and the problem is solved. That's because the default here is TaskCreationOptions.None.

See here for an in depth discussion of the difference.

Upvotes: 4

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