Non-awaited async methods run on the UI thread?

Question

I want to have a method (Let\'s call it M1) execute some async code in a loop (Let\'s call that second method M2). On every iterat

Answer 1

Yes. (assuming you use Synchronization Context that returns to UI thread - i.e. one from WinForm/WPF).

Note that it also means you can't schedule CPU-intensive operations that way as it will run on UI thread.

Using void async is quite standard method of handling events in WinForms:

void async click_RunManyAsync(...)
{
   await M1();
}

void async M1()
{
     foreach (...)
     {
        var result = await M2(); 
        uiElement.Text = result; 
     }
}

async Task<string> M2()
{
    // sync portion runs on UI thread
    // don't perform a lot of CPU-intensive work

    // off main thread, same synchronization context - so sync part will be on UI thread. 
    var result = await SomeReallyAsyncMethod(...); 

    // sync portion runs on UI thread
    // don't perform a lot of CPU-intensive work
}