public async Task Perform()
{
while (sourceProvider.HasNext())
{
var item = await sourceProvider.GetNext();
var metadatas = new ConcurrentDictionary <string, IMetadata>();
metadataProviders.AsParallel().ForAll(async mp => metadatas.TryAdd(mp.Name, await mp.GetMetadata(item)));
databaseProvider.Add(item, metadatas);
}
}
