Flat combining and the synchronization-parallelism tradeoff

Traditional data structure designs, whether lock-based or lock-free, provide parallelism via fine grained synchroniza- tion among threads. We introduce a new synchronization paradigm based on coarse locking, which we call flat combining. The cost of synchronization in flat combining is so low, that having a single thread holding a lock perform the combined access requests of all others, delivers, up to a certain non-negligible concurrency level, better performance than the most effective parallel finely synchronized implementations. We use flat-combining to devise, among other structures, new lin-earizable stack, queue, and priority queue algorithms that greatly outperform all prior algorithms.