File object cache for DirectoryStore #381
Description
It would be nice to have a file object cache for DirectoryStore (likely using LRU). The benefit here would be twofold. First we could reuse the same file object for multiple reads as opposed to tossing it after each one. This benefit becomes more notable when considering memory-mapping. ( #265 ) ( #377 ) Second we could constrain the number of file descriptors around at any one time by fixing the cache size. This latter point has been an issue historically for some workflows. Though IDK how much it occurs with Zarr specifically.