C++ Move Semantics for Exception Safety and Optimization in Software Transactional Memory Libraries Justin Gottschlich, Jeremy Siek, Daniel A. Connors. Proceedings of the 2008 International Workshop on Implementation, Compilation, Optimization of Object-Oriented Languages, Programs and Systems (ICOOOLPS 2008) July, 2008. The goal of transactional memory (TM) is to reduce the complexity of parallel programming. Software transactional memory (STM) is an effective near-term solution for gaining experience with transactional memory and taking advantage of its benefits. STM systems rely on either traditional lock-based synchronization or non-blocking techniques. While non-blocking techniques offer natural scalability, the lock-based approaches require fewer changes to user-defined data structures. Some lock-based STM libraries rely on user-defined copy assignment operators during the commit phase of a transaction (under the deferred update policy) or during the abort phase of a transaction (under the direct update policy). Unfortunately, such operations may throw exceptions and prevent the commit or abort from completing, thereby leaving the program in a partially-committed or inconsistent state. In this paper we present a solution to this problem: our STM library moves objects back to global memory instead of copying them. The move operation transfers the resources of the source object to the target object and then zeroes out the source object. Implementing move operations in an exception safe manner is straightforward. The ability to move objects is a new feature in the next version of the C++ standard, supported by the addition of rvalue references. We demonstrate our solution within DracoSTM, a C++ lock-based STM library, and present a performance comparison of move versus copy for both direct and deferred updating. [ PDF ]