how to calculate execution time of a async method in c#

Question

So I have a Async method which does something asynchronously.

private async static void DoSomethingAsync (int i){}

I call it in a loop lets say 50 times.

for (int i = 0; i < 50; i++)
 {
    DoSomethingAsync (i);
 }

At the end of loop I want to calculate total processing time, I used Stopwatch but as you can imagine it gives me wrong time as it gets called as soon as after the loop, it does not wait for the DoSomethingAsync to finish processing.

how to tell Stopwatch to wait for all the 50 instances of DoSomethingAsync() to finish. I have seen this question, but I cant use Task here.

Solution 1

I don't know why you cannot use Task, my guess is that you are calling it within a Main method or something. So i will go out from that.

Like Martin Ullrich said i would change DoSomethingAsync method to return a task:

private async static Task DoSomethingAsync(int i)
{
    ...
}

Then create a new method that does the loop by adding the methods to a List<Task>:

private static async void PerformLoop()
{
    Stopwatch timer = new Stopwatch();
    timer.Start();
    List<Task> l = new List<Task>();
    for (int i = 0; i < 50; i++)
    {
        l.Add(DoSomethingAsync(i));
    }
    await Task.WhenAll(l);
    timer.Stop();

    Console.WriteLine(timer.Elapsed.TotalSeconds);
}

Now from where you did the loop before, in this case the Main method simply add the new method call in there:

static void Main(string[] args)
{
    PerformLoop();

    Console.ReadLine();
}

Solution 2

This is the downside of using async void. There is no way to do that without modifying the called method (so that it could call a callback, unlock a mutex etc.).

You can change your method to return async Task instead and create another method that just calls this method without awaiting which can then be used in places you previously needed the async void signature for.

Solution 3

async void why? don't do that, use asnyc Task, or a ActionBlocks or ParallelFor/ForEach. However purely for novelty (and not to be used as a true gauge), if you want to calculate time in a parallel process id consider putting a timer inside your parallel method and using a global variable and use Interlocked.Add Method Method for thread safety

private long CombinedMs;

...

private async static void DoSomethingAsync (int i)
{

   var sw = new StopWatch();
   sw.Start();
   ...
   sw.Stop();

   Interlocked.Add(ref CombinedMs,sw.ElapsedMillisecond);

}

Anyway, i think you need to go back to the drawing board on tasks... Good luck