Await for list of Tasks

Question

I\'m trying to do something like this:

foreach (var o in ObjectList) 
{ 
    CalculateIfNeedToMakeTaskForO(o);

    if (yes) 
        TaskList.Add(OTaskAsync         


        

Answer 1

You are looking for Task.WaitAll (assuming your TaskList implemented IEnumerable<Task>)

Task.WaitAll(TaskList.ToArray());

Edit: Since WaitAll only takes an array of task (or a list of Task in the form of a variable argument array), you have to convert your Enumerable. If you want an extension method, you can do something like this:

public static void WaitAll(this IEnumerable<Task> tasks) 
{
    Task.WaitAll(tasks.ToArray());
}      

TaskList.WaitAll();

But that's really only syntactic sugar.

Answer 2

You are looking for Task.WhenAll:

var tasks = ObjectList
    .Where(o => CalculateIfNeedToMakeTaskForO(o))
    .Select(o => OTaskAsync(o))
    .ToArray();
var results = await Task.WhenAll(tasks);
var combinedResults = results.Select(r => "result for O is: " + r);