Supporting Nested Transactional Memory in LogTM

Nested Transactional Memory (TM) facilitates software composition by letting one module invoke another without either knowing whether the other uses transactions. Closed nested transactions extend isolation of an inner transaction until the top-level transaction commits. Implementations may flatten nested transactions into the top-level one, resulting in a complete abort on conflict, or allow partial abort of inner transactions. Open nested transactions allow a committing inner transaction to immediately release isolation, which increases parallelism and expressiveness at the cost of both software and hardware complexity.