Wait-free Dynamic Transactions for Linked Data Structures

Abstract

Transactional data structures support threads executing a sequence of operations atomically. Dynamic transactions allow operands to be generated on the fly and allows threads to execute code in between the operations of a transaction, in contrast to static transactions which need to know the operands in advance. A framework called Lock-free Transactional Transformation (LFTT) allows data structures to run high-performance transactions, but it only supports static transactions. We extend LFTT to add support for dynamic transactions and wait-free progress while retaining its speed. The thread-helping scheme of LFTT presents a unique challenge to dynamic transactions. We overcome this challenge by changing the input of LFTT from a list of operations to a function, forcing helping threads to always start at the beginning of the transaction, and allowing threads to skip completed operations through the use of a list of return values. We thoroughly evaluate the performance impact of support for dynamic transactions and wait-free progress and find that these features do not hurt the performance of LFTT for our test cases.