RingSTM: Scalable Transactions with a Single Atomic Instruction

Existing Software Transactional Memory (STM) designs attach metadata to ranges of shared memory; subsequent runtime instructions read and update this metadata in order to ensure that an in-flight transaction’s reads and writes remain correct. The overhead of metadata manipulation and inspection is linear in the number of reads and writes performed by a transaction, and involves expensive read-modify-write instructions, resulting in substantial overheads.

We consider a novel approach to STM, in which transactions represent their read and write sets as Bloom filters, and transactions commit by enqueuing a Bloom filter onto a global list. Using this approach, our RingSTM system requires at most one read-modify-write operation for any transaction, and incurs validation overhead linear not in transaction size, but in the number of concurrent writers who commit. Furthermore, RingSTM is the first STM that is inherently livelockfree and privatization-safe while at the same time permitting parallel writeback by concurrent disjoint transactions. We evaluate three variants of the RingSTM algorithm, and find that it offers superior performance and/or stronger semantics than the state-of-the-art TL2 algorithm under a number of workloads.