Per https://stackoverflow.com/questions/38133870/how-the-parameter-numberofconcurrentthreads-is-used-in-createiocompletionport, it seems that `NumberOfConcurrentThreads` controls what happens when multiple threads call `GetQueuedCompletionStatus`.  

But since a given instance of `IocpProactor` only calls `GetQueuedCompletionStatus` from a single thread, probably this arg doesn't matter, and the value `1` would be more explicit about the pattern asyncio is using?  A huge number is, presumably, either not relevant or, at worst, wasteful of some kernel resource.  

Am I correct that only one thread calls `GetQueuedCompletionStatus` on a given `iocp` object in asyncio under Windows `IocpProactor`?