caching the result from a [n async] factory method iff it doesn't throw

Question

UPDATE: Heavily revised after @usr pointed out I\'d incorrectly assumed Lazy\'s default thread safety mode was LazyThreadSafetyMode.PublicationOn

Answer 1

For now, I am using this:

public class CachedAsync
{
    readonly Func> _taskFactory;
    T _value;

    public CachedAsync(Func> taskFactory)
    {
        _taskFactory = taskFactory;
    }

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

    async Task Fetch()
    {
        if (_value == null)
            _value = await _taskFactory();
        return _value;
    }
}

While it works in my scenario (I don't have multiple triggering threads etc.), it's hardly elegant and doesn't provide thread-safe coordination of either

• a single attempt in progress a la LazyThreadSafetyMode.ExecutionAndPublication OR
• a stable result after >= 1 success a la LazyThreadSafetyMode.PublicationOnly