A queue for unique indices (integers) with O(1) push/pop and O(1) lookup/removal. It is a doubly-linked list with all its nodes stored inside a single Vec. The queue is most memory efficient when the integers are relatively small and densely packed. The implementation is similar to
index_queue is more specialized: it allows querying whether an index already exists as well as removal by index, but does not allow duplicate indices.
This crate was originally created to implement a cooperative FIFO task scheduler (