To get Result from Task.Run without await

Question

I have a snippet that looks like this,

private void btn_Click(object sender, EventArgs e)
{
   try
   {
      var res = Task.Run(() => DoTask(param1, param2));
      if(res.IsCompleted)
      { 
          MessageBox.Show("Done");
      }
       MessageBox.Show("DoTask isn't called yet.");
   }
   catch
   {
       MessageBox.Show("Something wrong");
   }
}

The DoTask method looks like this

private async Task<bool> DoTask(int p1, int p2)
{
    // run long tasks   

}

I'd want to show Done message after the task is done. But this never works. Instead the message DoTask isn't called yet. is always called before DoTask does tasks.

Change the signature to `async void` and use `await`. Anything else would just freeze the UI, removing any benefit you'd get from `Task.Run` — Panagiotis Kanavos, Mar 06 '20 at 17:41
I am wildly guessing you want to do something after task is complete without blocking current thread, see [this](https://stackoverflow.com/q/13211334/1997232). — Sinatr, Mar 06 '20 at 17:42
Can you elaborate on why you are using `Task.Run` when `DoTask` is asynchronous? `Task.Run` should not be required in this case. — Thomas Barnekow, Mar 06 '20 at 17:54
All of the answers posted thus far are dangerously wrong; they all produce situations in which you can easily deadlock your process. You do NOT get a result from a task without `await` *unless you already know that the task has completed*. Asynchronous tasks **need to be awaited asynchronously**. That's why they are asynchronous! — Eric Lippert, Mar 06 '20 at 19:06

score 0 · Answer 1 · answered Mar 06 '20 at 17:50

Panagiotis' answer is the way to go. Should you have the same situation in a method that is not an event handler and you can't use async for some reason, here's the next best option:

Task<bool> task = Task.Run(() => DoTask(param1, param2));
bool res = task.GetAwaiter().GetResult();

score 0 · Answer 2 · answered Mar 07 '20 at 00:50

To get Result from Task.Run without await

The proper way to get a result from an asynchronous task is to use await:

private async void btn_Click(object sender, EventArgs e)
{
   try
   {
      var res = await Task.Run(() => DoTask(param1, param2));
      if(res)
      { 
          MessageBox.Show("Done");
      }
       MessageBox.Show("DoTask isn't called yet.");
   }
   catch
   {
       MessageBox.Show("Something wrong");
   }
}

Note that you should usually avoid async void, but since this code is an event handler, the async void is OK.

score -2 · Answer 3 · answered Mar 06 '20 at 18:21

-2

Simple Way:

bool result = DoTask(paran1, param2).Result;

No need to use Task.Run(). But you can use it in the following way (BAD WAY):

bool result = Task.Run(() => DoTask(paran1, param2).Result).Result;

answered Mar 06 '20 at 18:21

Haddad

301
3
5

1

Do not follow the advice in this answer. This causes deadlocks. – Eric Lippert Mar 06 '20 at 19:05

To get Result from Task.Run without await

3 Answers3