auto-revert-notify-watch-descriptor-hash-list is a variable defined in `autorevert.el'.
Its value is

#s(hash-table size 65 test equal rehash-size 1.5 rehash-threshold 0.8 data ())

A hash table collecting all file watch descriptors.
Hash key is a watch descriptor, hash value is a list of buffers
which are related to files being watched and carrying the same
default directory.