class Bootsnap::LoadPathCache::Cache

def load_dir(dir)

is "/a/b".
e.g. given "/a/b/c/d" exists, and the path is ["/a/b"], load_dir("c/d")
What is the path item that contains the dir as child? 
def load_dir(dir)
  reinitialize if stale?
  @mutex.synchronize { @dirs[dir] }
end