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Editorial Team
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Asked: 2026-05-27T22:07:28+00:00

I’m reading a book called Pro .NET 4 Parallel Programming in C# by Adam

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I’m reading a book called Pro .NET 4 Parallel Programming in C# by Adam Freeman. In Chapter 2 page 13 it talks about using Task<int> to return a result by using task1.Result to wait for it to finish. I don’t understand why task2 has to wait for task1 to finish. They are on different threads.

It’s something like below:

Task<int> task1 = new Task<int>(() => { ... ; return sum });
task1.Start();
Console.WriteLine("Result 1: {0}", task1.Result);

Task<int> task2 = new Task<int>(() => { ... ; return sum });
task2.Start();
Console.WriteLine("Result 2: {0}", task2.Result);

If I move to following line to the bottom it seems like task1 still executes first no matter how many times I tried.

Console.WriteLine("Result 1: {0}", task1.Result);

Why is this happening?

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1 Answer

  1. Editorial Team

    The task that actually finishes first — that is, hits its return statement first — is, formally, unpredictable. They can finish their work before you accept their Results.

    If the work your sample tasks do is not very large, it stands to reason that task1 will finish first even if you don’t accept its Result (or in Java threading lingo, join it) first. That’s because you Started it first.

    Presumably you somehow know that task1 finished first. Is there a Console.WriteLine buried in the code for your tasks? If so, keep in mind that the Console subsystem serializes operations, so the first of your tasks to use it will do so completely before the second one can start. Think of it this way: your two tasks race to Console, and the winner takes all.

    task1 has an unfair advantage in this race, because it’s off and running before your main thread even starts constructing task2 with your second new.

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