How can I write a lock free structure?

Question

In my multithreaded application and I see heavy lock contention in it, preventing good scalability across multiple cores. I have decided to use lock free programming to solv

Answer 1

in re. Suma's answer, Maurice Herlithy shows in The Art of Multiprocessor Programming that actually anything can be written without locks (see chapter 6). iirc, This essentially involves splitting tasks into processing node elements (like a function closure), and enqueuing each one. Threads will calculate the state by following all nodes from the latest cached one. Obviously this could, in worst case, result in sequential performance, but it does have important lockless properties, preventing scenarios where threads could get scheduled out for long peroids of time when they are holding locks. Herlithy also achieves theoretical wait-free performance, meaning that one thread will not end up waiting forever to win the atomic enqueue (this is a lot of complicated code).

A multi-threaded queue / stack is surprisingly hard (check the ABA problem). Other things may be very simple. Become accustomed to while(true) { atomicCAS until I swapped it } blocks; they are incredibly powerful. An intuition for what's correct with CAS can help development, though you should use good testing and maybe more powerful tools (maybe SKETCH, upcoming MIT Kendo, or spin?) to check correctness if you can reduce it to a simple structure.

Please post more about your problem. It's difficult to give a good answer without details.

edit immutibility is nice but it's applicability is limited, if I'm understanding it right. It doesn't really overcome write-after-read hazards; consider two threads executing "mem = NewNode(mem)"; they could both read mem, then both write it; not the correct for a classic increment function. Also, it's probably slow due to heap allocation (which has to be synchronized across threads).