STAThread and async Main gotcha
This took me quite a while to debug, because I was constantly wrongly assuming my threading and synchronization context handling was wrong. At the end of the day it was very simple, I just couldn’t see the forest for the trees.
I have a gutted out WinForms application, no forms, just manually handling bunch of stuff via ApplicationContext. For example, something like this.
[STAThread]
static void Main()
{
ApplicationConfiguration.Initialize();
Application.Run(new MyApplicationContext());
}
Which is pretty standard. But at one point I had to do some “asynchronous initialization” and switched to this (again, an example).
[STAThread]
static async Task Main()
{
ApplicationConfiguration.Initialize();
await foo.InitializeAsync();
Application.Run(new MyApplicationContext());
}
And suddenly everything started to fell apart. I.e: System.Threading.ThreadStateException: 'Current thread must be set to single thread apartment (STA) mode before OLE calls can be made. Ensure that your Main function has STAThreadAttribute marked on it.'.
As I mentioned at the beginning, I immediately jumped into conclusion, that I’m doing something wrong regarding my threading and synchronization context. But as I was digging into it, everything seemed correct. But I kept digging. Oh, boy. Luckily, I realized what the issue was.
The async Main is no magic. In fact I blogged about it roughly 5 years ago. The end code is more or less this.
static void Main() => OldMain().GetAwaiter().GetResult();
[STAThread]
static async Task OldMain()
{
ApplicationConfiguration.Initialize();
await Foo.InitializeAsync();
Application.Run(new MyApplicationContext());
}
Now the STAThread attribute is no longer on real Main, but on some “random” method.
With that, I simply manually created Main method that would be otherwise created by compiler and put STAThread attribute there.
Job done. But what a journey!
