WFR-TM: Wait-free readers without sacrificing speculation of writers

Abstract

Transactional Memory (TM) is a promising concurrent programming paradigm which employs transactions to achieve synchronization in accessing common data known as transactional variables. A transaction may either commit, making its updates to transactional variables visible, or abort, discarding its updates.We introduce WFR-TM, a TM algorithm which attempts to combine the advantages of pessimistic and optimisticTM. In a pessimistic TM, no transaction ever aborts; however, current pessimistic TM implementations, execute update transactions sequentially, decreasing the degree of achieved parallelism. In optimistic TM, transactions are executed concurrently and they commit if they have encountered no conflict during their execution.In WFR-TM, read-only transactions not only are wait-free, but also they never execute expensive synchronization operations (like CAS, LL/SC, etc.). This is achieved without sacrificing the parallelism between update transactions. Update transactions synchronize pessimistically with concurrently executed read-only transactions but they synchronize optimistically with each other.