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 by making its updates to transactional variables visible or abort by discarding all its changes.We introduce WFR-TM, a TM algorithm which attempts to combine the advantages of pessimistic and optimistic TM. In a pessimistic TM, no transaction ever aborts; however, update transactions are executed sequentially, thus decreasing the degree of achieved parallelism. In optimistic TM, transactions are executed concurrently and they commit if they have not encountered any conflict during their execution.In WFR-TM, read-only transactions are wait-free and they never execute expensive synchronization operations, like CAS, Fetch&Increment, Swap, etc. This is achieved without sacrificing the parallelism between update transactions. Update transactions synchronize pessimistically with concurrently executed read-only transactions and they synchronize optimistically with each other.