|
poll is fairly portable, but still has scaling problems. To get beyond scaling problems, you usually need something OS-specific, such as epoll (Linux), kqueue (BSDs of some kind), etc. One of the things I'd expect of a cross-platform networking library would be to use the best available abstraction, especially on major platforms such as linux, and perhaps fall back to select on odd platforms. Of course, your docs need to point out what the behavior is. The problem with poll/select is that you need to pass (transfer) to the kernel the entire list of events you're interested in, just to wait for a single event. Each time you re-enter your event loop you need to do this, and if you have thousands of connections, it will break down, because poll is O(number of connections). epoll, for example, works around this by having an "epoll FD", which on the kernel side contains all the events you're interested in. You wait by just waiting on that epoll fd with epoll_wait, but you don't specify the events you're interested in when you wait: you do that ahead of time, with other system calls. This allows you to change the event list only when you need to, which is much less frequent than some data arrived from somewhere. The API is supposed to be O(1), instead of O(number of connections) per wait call. My understanding is the kqueue works similarly, but I'm a Linux guy, so I can't really tell you. select also has other problems w.r.t. FDs with high numbers. |