I've written a fairly wide variety of multithreaded code in the past ten years or so, and I think the only real trouble I've had is with algorithms that work st

I've written a fairly wide variety of multithreaded code in the past ten years or so, and I think the only real trouble I've had is with algorithms that work step by step, each step dependent on the previous results. That's effectively impossible to parallelize without fundamentally changing the algorithm. Otherwise, even if you have large chunks of shared memory, it's usually possible to work around that without locks.