UNLOCKING CONCURRENCY

Multicore architectures are an inflection point in mainstream software development because they force developers to write paral-lel programs. In a previous article in Queue, Herb Sutter and James Larus pointed out, “The concur-rency revolution is primarily a software revolution. The difficult problem is not building multicore hardware, but programming it in a way that lets mainstream applica-tions benefit from the continued exponential growth in CPU performance.” In this new multicore world, developers must write explicitly parallel applications that can take advantage of the increasing number of cores that each successive multicore generation will provide. Parallel programming poses many new challenges to the developer, one of which is synchronizing concurrent access to shared memory by multiple threads. Program-mers have traditionally used locks for synchronization, but lock-based synchronization has well-known pitfalls. Simplistic coarse-grained locking does not scale well, while more sophisticated fine-grained locking risks intro-ducing deadlocks and data races. Furthermore, scalable libraries written using fine-grained locks cannot be easily composed in a way that retains scalability and avoids deadlock and data races. TM (transactional memory) provides a new concur-rency-control construct that avoids the pitfalls of locks and significantly eases concurrent programming. It brings to mainstream parallel programming proven concur-more queue: www.acmqueue.co