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'd go with AsyncLazy (slightly modified version):

public class AsyncLazy : Lazy> 
{ 
    public AsyncLazy(Func valueFactory) : 
        base(() => Task.Run(valueFactory)) { }

    public AsyncLazy(Func> taskFactory) : 
        base(() => Task.Run(() => taskFactory())) { } 

    public TaskAwaiter GetAwaiter() { return Value.GetAwaiter(); } 
}

And consume it like this:

private AsyncLazy asyncLazy = new AsyncLazy(async () =>
                                    { 
                                        await DoStuffOnlyOnceAsync()
                                        return true;
                                    });

Note i'm using bool simply because you have no return type from DoStuffOnlyOnceAsync.

Edit:

Stephan Cleary (of course) also has an implementation of this here.