Question

I have a method that returns XML elements, but that method takes some time to finish and return a value.

What I have now is

foreach (var t in s)
{
    r.add(method(test));
}

but this only runs the next statement after previous one finishes. How can I make it run simultaneously?

Answer 1

You should be able to use tasks for this:

//first start a task for each element in s, and add the tasks to the tasks collection
var tasks = new List<Task>();
foreach( var t in s)
{
    tasks.Add(Task.Factory.StartNew(method(t)));
}

//then wait for all tasks to complete asyncronously
Task.WaitAll(tasks);

//then add the result of all the tasks to r in a treadsafe fashion
foreach( var task in tasks)
{
  r.Add(task.Result);
}

EDIT
There are some problems with the code above. See the code below for a working version. Here I have also rewritten the loops to use LINQ for readability issues (and in the case of the first loop, to avoid the closure on t inside the lambda expression causing problems).

var tasks = s.Select(t => Task<int>.Factory.StartNew(() => method(t))).ToArray();

//then wait for all tasks to complete asyncronously
Task.WaitAll(tasks);

//then add the result of all the tasks to r in a treadsafe fashion
r = tasks.Select(task => task.Result).ToList();