alt Hacker NewsIf I understand this correctly, it basically has the second thread wait until the first one experiences a hardware interrupt, which implicitly synchronizes memory. This avoids the first thread from needing any synchronization primitives that would slow it down.
Sort of. Basically you have a situation where one thread needs to see another thread's memory accesses in sequential consistent order. If you can determine the other thread has synchronized its memory accesses at some point, then all its memory accesses before that are in observably sequentially consistent.
The thing is you don't know exactly when that synchronization took place so your code logic has to take that into account. In the case of hazard pointers, false positives are ok and false negatives, i.e. thread is using reference that was not detected, cannot occur.
There's 2 or 3 other tricks you can make hazard pointers wait-free. Getting rid of the conditional branching in the instruction pipeline gives you a considerable speed up.