ASP.Net WebApi STA Mode

Question

This post scratches off WebApi from being able to run in STA mode. But this post is also 2 years old.

I've been digging into the newer WebApi2 but can't seem to find a way to make MessageHandlers run in STA mode.

So has anyone found a way of running WebApi or WebApi2 in STA mode?

Answer 1

So it seems that if you want to switch the entire request processing thread to STA mode, you're better off with MVC. However, if your handler does a one off task that doesn't involve switching the entire thread into STA mode, Web API makes it pretty easy. Here's how I did it:

public class StaHandler : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        // consider moving it to singleton instance to improve performance
        var staTaskScheduler = new StaTaskScheduler(100);

        return Task.Factory.StartNew<HttpResponseMessage>(() =>
        {
            //somethign that does its magic and returns a HttpResponseMessag
            return new HttpResponseMessage();
        }, cancellationToken,
            TaskCreationOptions.None,
            staTaskScheduler);
    }
}

Things to consider:

• Creating StaTaskScheduler is heavy. Consider moving it to a singleton or ensure it is initialized only once during App_Start
• Thread Pool Size (100 in my example) can also play a role in how well this scales. Unfortunately, there is no magic formula to get this right. I created Web Performance Load Tests to figure out a sweet spot on my servers.