Async threadsafe Get from MemoryCache

Question

I have created a async cache that uses .NET MemoryCache underneath. This is the code:

public async Task GetAsync(string key, Func

        

Answer 1

Although there is an already accepted answer, I'll post a new one with Lazy approach. Idea is: to minimize the duration of lock block, if the key doesn't exists in cache, put a Lazy to cache. That way all threads using the same key at the same time will be waiting the same Lazy's value

public Task GetAsync(string key, Func> populator, TimeSpan expire, object parameters)
{
    if (parameters != null)
        key += JsonConvert.SerializeObject(parameters);

    lock (_cache)
    {
        if (!_cache.Contains(key))
        {
            var lazy = new Lazy>(populator, true);
            _cache.Add(key, lazy, DateTimeOffset.Now.Add(expire));
        }
    }

    return ((Lazy>)_cache.Get(key)).Value;
}

Version2

public Task GetAsync(string key, Func> populator, TimeSpan expire, object parameters)
{
    if (parameters != null)
        key += JsonConvert.SerializeObject(parameters);

    var lazy = ((Lazy>)_cache.Get(key));
    if (lazy != null) return lazy.Value;

    lock (_cache)
    {
        if (!_cache.Contains(key))
        {
            lazy = new Lazy>(populator, true);
            _cache.Add(key, lazy, DateTimeOffset.Now.Add(expire));
            return lazy.Value;
        }
        return ((Lazy>)_cache.Get(key)).Value;
    }
}

Version3

public Task GetAsync(string key, Func> populator, TimeSpan expire, object parameters)
{
    if (parameters != null)
        key += JsonConvert.SerializeObject(parameters);

    var task = (Task)_cache.Get(key);
    if (task != null) return task;

    var value = populator();
    return 
     (Task)_cache.AddOrGetExisting(key, value, DateTimeOffset.Now.Add(expire)) ?? value;
}