Firing off multiple Tasks asynchronously and waiting for them to complete [duplicate]

Question

I have a situation where I want to fire off a user-defined number of tasks asynchronously and wait for all of them to complete. Simplified, here's what I'm dealing with:

[TestMethod]
public async Task Start() {
        var numDrivers = 2;
        while (numDrivers != 0) {
            var rnd = new Random();
            var r = rnd.Next(itemArray.Count);
            var target = itemArray[r];
            var proxyDriver = GetProxiedDriver();
            Task.Run(() => HandleIntro(proxyDriver, target));
            numDrivers--;
        }
 }

For some context - these are Selenium webdrivers getting spun up to run some UI tests. I see the browsers pop up, but as soon as the last Task.Run() completes, all execution stops. How do I fire off n drivers to run asynchronously while waiting for them all to complete before stopping execution?

I've tried await Task.Run(() => HandleIntro(proxyDriver, target)); but this awaits the task and they don't run simultaneously.

HandleIntro:

private async Task HandleIntro(FirefoxDriver driver, string target) {
    // do stuff
}

Answer 1

It's rather simple with async-await. You have Task.WhenAll which itself returns an awaitable which can be asynchronously waited for all tasks to complete:

[TestMethod]
public async Task Start() 
{
   var numDrivers = 2;
   List<Task> tasks = new List<Task>();

   while (numDrivers != 0) 
   {
       var rnd = new Random();
       var r = rnd.Next(itemArray.Count);

       var target = itemArray[r];
       var proxyDriver = GetProxiedDriver();

       tasks.Add(Task.Run(() => HandleIntro(proxyDriver, target)));
       numDrivers--;
   }

   await Task.WhenAll(tasks);
}