C# regarding running multiple task

Question

State1 & state2 will run parallel or State1 will run first and later State2 will run ?

please guide me. thanks

    var stage1 = Task.Run(() =>
    {

    });

    var stage2 = Task.Run(() =>
    {

    });

    // Block until both tasks have completed.
    // This makes this method prone to deadlocking.
    // Consider using 'await Task.WhenAll' instead.
    Task.WaitAll(stage1, stage2);

Answer 1

@T.Zacks , based on my test, the code you provided will run parallel.

I make a code example and you could have a look.

Code:

    var timer = new Stopwatch();  
    timer.Start();  
    Task.WaitAll(stage1, stage2);  
    timer.Stop();  
    TimeSpan timeTaken = timer.Elapsed;  
    string foo = "Time taken: " + timeTaken.TotalMilliseconds;  
    Console.WriteLine(foo);  

Result:

As the above result showed, we spend about 5000 Milliseconds to complete the two tasks. The stage2 will be completed first, because it only needs 1000 Milliseconds.

Note: I can not code the first two line's code, so I make a picture about the code.

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Answer 2

Each time you "run" a task it begins running at some point in the future. When that is depends on different factors but as far as your code is concerned you can assume it starts running immediately while your main thread continues running. Therefore stage1 will start running then stage2 will start running and then your main thread will block waiting for both to complete. Which one runs first and which one completes first is non-deterministic as it depends on factors related to what is running and what is going on in the system right now.

If you want to make these tasks run in sequential order then start one and then wait for it to finish before starting the second one. Of course the downside is that the total execution times is now : S1 + S2 instead of MAX(S1, S2) of running them in parallel.

var stage1 = await Task.Run(...);   //Run task 1 and wait for it to complete
var stage2 = await Task.Run(...);   //Run task 2 and wait for it to complete

//Both tasks are done so don't need to wait anymore.

Also note that, depending on what they are doing, you tasks may not even run async at all. Again, this is dependent upon multiple factors but for purposes of your code assume they run async as you coded for.