Enforce an async method to be called once

Question

Say I have a class that needs to perform some async initialization using an InitializeAsync() method. I want to make sure that the initialization is performed only once. If

Answer 1

I have a blog post that covers a few different options for doing "asynchronous constructors".

Normally, I prefer asynchronous factory methods, because I think they're simpler and a bit safer:

public class MyService
{
  private MyService() { }

  public static async Task CreateAsync()
  {
    var result = new MyService();
    result.Value = await ...;
    return result;
  }
}

AsyncLazy is a perfectly good way of defining a shared asynchronous resource (and may be a better conceptual match for a "service", depending on how it is used). The one advantage of the async factory method approach is that it's not possible to create an uninitialized version of MyService.