A fast unique identifier supply with local pooling and replay support.

One often has a desire to generate a bunch of integer identifiers within a single process that are unique within that process. You could use UUIDs, but they can be expensive to generate; you don't want to have your threads contending for a single external counter if the identifier is not going to be used outside the process.

concurrent-supply builds a tree-like structure which can be split; you can make smaller unique supplies and then you allocate from your supplies locally. Internally it pulls from a unique supply one block at a time as you walk into parts of the tree that haven't been explored.