[pizlonator]

You’re talking about interfaces for waiting on multiple kernel resources but the new futex interface enables you to wait for multiple user resources.

Though it can emulate a win32 api for waiting on multiple “objects”, it’s strictly more powerful than WaitForMultiple if you are dealing with user objects since futexes impose very few constraints on how your user synchronization object is shaped and how it works.

So, the new interface is totally different from things like epoll. In one case the kernel is helping you wait for multiple user objects and in the other case it’s helping you wait for multiple kernel objects. The distinction is intentional because the whole point is that the user object that has the futex can be shaped however user likes, and can implement whatever synchro protocol the use likes.

Finally, it’s worth remembering that futex interfaces are all about letting you avoid going into kernel unless there is actually something to wait for. The best part of the api is that it helps you to avoid calling it. So for typical operations, if the resource being waited on can have its wait state represented as a 32-bit int in user memory, the futex based apis will be a lot faster.