Using the Stopwatch with Async methods

Question

I have some code as follows:

public void Start()
{
    var watch = new Stopwatch();
    watch.Start();

    Task.Factory.StartNew(MyMethod1);
    Task.Factory.StartNew(MyMethod2);

    watch.Stop();
    Log(watch.ElapsedMilliseconds);
    Task.Factory.StartNew(MyMethod3);
}

Because MyMethod1 and MyMethod2 are called Asynchronously watch.Stop() gets called at the wrong time. How I can ensure that .Stop gets called and logged after MyMethod1 and MyMethod2 finish BUT ensure that MyMethod3 does not have to wait.

I want to keep all Stopwatch functionality in my Start() method and not have the logging in any of my 3 methods i.e. MyMethod1, MyMethod2 and MyMethod3

Answer 1

You can use the Task.Factory.ContinueWhenAll method.

watch.Start();
var t1 = Task.Factory.StartNew(MyMethod1);
var t2 = Task.Factory.StartNew(MyMethod2);
Task.Factory.ContinueWhenAll(new [] {t1, t2}, tasks => watch.Stop());

If you're targeting for .NET 4.5 and upper, you can also use the method Task.WhenAll. It returns a task that will complete when all of the passed Task objects have completed.

Task.WhenAll(t1, t2).ContinueWith(t => watch.Stop());