libnative (fast, low-latency native I/O) and libgreen (libuv backed and great for large numbers of infrequent/idle messengers) are both awesome and provide some great options for network server I/O, particularly since you can mix-and-match them.
However there's a seemingly unsolved problem in Rust: multiplexing I/O operations with channels. I think this can be fixed in a purely additive manner (i.e everything else that exists today is great!) with a new feature borrowed from Erlang: the ioserver (noting that Erlang also implements libgreen-style synchronous I/O in addition to ioserver) Ignoring Erlang for a second, the naive solution to the I/O + channel multiplexing is magic select API that can handle both. In my experience (i.e. I wrote and support this approach in a system some people actually use) the backend implementation, especially across POSIX and Windows, ends up quite ugly. There's a better option though... if you want to multiplex IO with channel messages, turn everything into channel messages in one place: the "ioserver" Solution: Centralize I/O event loops into a separate thread (pool if necessary, probably not). Erlang and 0MQ work this way. Erlang implements an API called a "port" to talk to the ioserver. In Rust perhaps you could have a type that implements the same trait as channels? The ioserver becomes the central place to optimize the nitty gritty of taking I/O requests from the rest of the program and multiplexing them with other (i.e channel) events in the system. The basic formula is: - Have the ioserver block for events using libuv or what have you, and have an OS-specific I/O handle (i.e. a pipe) to unblock the selector in the event of in-process communication - Use lock-free mechanisms so if the selector isn't stuck in a system call we can use more efficient coordination of registering and unregistering I/O op interests (Note: libuv is an I/O completions library and not a selector library so the proposed solution is admittedly a bit handwavey) Mixing a pipe-based wakeup mechanism with lock-free operations to eliminate unnecessary system calls has been used somewhat successfully in the Netty I/O library for the JVM. -- Tony Arcieri
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