C# TPL how to know that all tasks are done?

Question

I have the Loop which generates tasks.

Code:

Task task = null;
foreach (Entity a in AAAA)
{
  // create the task 
  task = new Task(() => {
    myMethod(a);
  },  Token, TaskCreationOptions.None);
  task.Start();
}

As you can see in each iteration task object has new initialization (..new Task(() =>..) How can I know that all tasks done?

Answer 1

var allTasks = new List<Task>();
foreach (Entity a in AAAA)
{
  // create the task 
  task = new Task(() => {
    myMethod(a);
  },  Token, TaskCreationOptions.None);

  // Add the tasks to a list
  allTasks.Add(task);
  task.Start();
}

// Wait until all tasks are completed.
Task.WaitAll(allTasks.ToArray());

Answer 2

You'll need to keep references to all the tasks created in the loop. Then you can use the Task.WaitAll method (see MSDN reference). You can either create an array and assign tasks to elements of the array (in C# 2.0) or you can use LINQ:

var tasks = 
   AAAA.Select((Entity a) => 
      Task.Factory.StartNew(() => { myMethod(a); },
         Token, TaskCreationOptions.None)).ToArray();
Task.WaitAll(tasks)

If you don't need to use tasks (explicitly) then Henk's suggestion to use Parallel.ForEach is probably a better option.

Answer 3

I f you replace this with a

 Parallel.ForEach(...,  () => myMethod(a), ...)

Then you get an automatic Wait on all tasks at the end of the ForEach.

And maybe run the ForEach from a separate Task.