A cache for your async tasks so that you can await the same result multiple times

AsyncGeneratorCache.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

namespace DataStructures
{
    public class AsyncGeneratorCache<TKey, TValue>
    {
        private Func<TKey, Task<TValue>> _generate;
        private Dictionary<TKey, Task<TValue>> _promises = new Dictionary<TKey, Task<TValue>>();

        public AsyncGeneratorCache(Func<TKey, Task<TValue>> generatorFunction)
        {
            _generate = generatorFunction;
        }

        public async Task<TValue> Get(TKey key)
        {
            if (!_promises.ContainsKey(key))
                _promises[key] = _generate(key);

            return await _promises[key];
        }

        public void Set(TKey key, TValue value)
        {
            _promises[key] = Task.Run(() => value);
        }

        public void Remove(TKey key)
        {
            _promises.Remove(key);
        }

        public IEnumerable<TKey> Keys { get { return _promises.Keys; } }
    }
}