Cats STM

Cats STM is a library for writing composable in-memory transactions which will handling correct locking, optimistic concurrency and automatic retries for you. It is intended as a safe, composable alternative to locks and semaphores that also allows a higher level of concurrency.

Transactional and Safe

Write Txn expressions in terms of mutable TVars (analogous to Ref from Cats Effect). Run Txn[A] expressions transactionally to obtain an IO[A] (or F[A] for the Async[F] of your choice). The STM runtime will determine what locks need to be acquired and in what order to avoid deadlock.

Composable

Trivially compose transactional expressions into larger ones without explicit locking or requiring any knowledge of the internals of the subexpressions and what locks they require.

Automatic retries

Specify pre-conditions and the committing of a transaction will be automatically retried until the pre-conditions are satisifed.

Fine-grained, optimistic concurrency

There are no global locks and per-TVar locks are acquired only when a transaction has succeeded and should be committed.