1:55:24no-defun-allowedClick's choice to keep keys "pinned" in entries makes reasoning about updates much easier.
1:58:40no-defun-allowedFor example, one thread could be updating an entry, while another removed that entry, then replaced it with an entry with a different key but the same value. Then the former thread could CAS out the value, and end up with the new key with a value intended for the old key.
2:04:27no-defun-allowedThe "insert tombstones only when group is full" concept is also hard to apply with multiple threads, as two threads inserting could fill a group, without either having observed that it was full.