concurrent-supply-0.1.8: A fast concurrent unique identifier supply with a pure API

Copyright(C) 2011-2013 Edward Kmett
LicenseBSD-style (see the file LICENSE)
MaintainerEdward Kmett <>
Safe HaskellTrustworthy




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.



data Supply Source

A user managed globally unique variable supply.


newSupply :: IO Supply Source

Grab a new supply. Any two supplies obtained with newSupply are guaranteed to return disjoint sets of identifiers. Replaying the same sequence of operations on the same Supply will yield the same results.

freshId :: Supply -> (Int, Supply) Source

Obtain a fresh Id from a Supply.

splitSupply :: Supply -> (Supply, Supply) Source

Split a supply into two supplies that will return disjoint identifiers

Unboxed API

freshId# :: Supply -> (#Int#, Supply#) Source

An unboxed version of freshId

splitSupply# :: Supply -> (#Supply, Supply#) Source

An unboxed version of splitSupply