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# wepoll - epoll for windows [![][ci status badge]][ci status link] This library implements the [epoll][man epoll] API for Windows applications. It is fast and scalable, and it closely resembles the API and behavior of Linux' epoll. ## Rationale Unlike Linux, OS X, and many other operating systems, Windows doesn't have a good API for receiving socket state notifications. It only supports the `select` and `WSAPoll` APIs, but they [don't scale][select scale] and suffer from [other issues][wsapoll broken]. Using I/O completion ports isn't always practical when software is designed to be cross-platform. Wepoll offers an alternative that is much closer to a drop-in replacement for software that was designed to run on Linux. ## Features * Can poll 100000s of sockets efficiently. * Fully thread-safe. * Multiple threads can poll the same epoll port. * Sockets can be added to multiple epoll sets. * All epoll events (`EPOLLIN`, `EPOLLOUT`, `EPOLLPRI`, `EPOLLRDHUP`) are supported. * Level-triggered and one-shot (`EPOLLONESTHOT`) modes are supported * Trivial to embed: you need [only two files][dist]. ## Limitations * Only works with sockets. * Edge-triggered (`EPOLLET`) mode isn't supported. ## How to use The library is [distributed][dist] as a single source file ([wepoll.c][wepoll.c]) and a single header file ([wepoll.h][wepoll.h]).<br> Compile the .c file as part of your project, and include the header wherever needed. ## Compatibility * Requires Windows Vista or higher. * Can be compiled with recent versions of MSVC, Clang, and GCC. ## API ### General remarks * The epoll port is a `HANDLE`, not a file descriptor. * All functions set both `errno` and `GetLastError()` on failure. * For more extensive documentation, see the [epoll(7) man page][man epoll], and the per-function man pages that are linked below. ### epoll_create/epoll_create1 ```c HANDLE epoll_create(int size); HANDLE epoll_create1(int flags); ``` * Create a new epoll instance (port). * `size` is ignored but most be greater than zero. * `flags` must be zero as there are no supported flags. * Returns `NULL` on failure. * [Linux man page][man epoll_create] ### epoll_close ```c int epoll_close(HANDLE ephnd); ``` * Close an epoll port. * Do not attempt to close the epoll port with `close()`, `CloseHandle()` or `closesocket()`. ### epoll_ctl ```c int epoll_ctl(HANDLE ephnd, int op, SOCKET sock, struct epoll_event* event); ``` * Control which socket events are monitored by an epoll port. * `ephnd` must be a HANDLE created by [`epoll_create()`](#epoll_createepoll_create1) or [`epoll_create1()`](#epoll_createepoll_create1). * `op` must be one of `EPOLL_CTL_ADD`, `EPOLL_CTL_MOD`, `EPOLL_CTL_DEL`. * `sock` must be a valid socket created by [`socket()`][msdn socket], [`WSASocket()`][msdn wsasocket], or [`accept()`][msdn accept]. * `event` should be a pointer to a [`struct epoll_event`](#struct-epoll_event).<br> If `op` is `EPOLL_CTL_DEL` then the `event` parameter is ignored, and it may be `NULL`. * Returns 0 on success, -1 on failure. * It is recommended to always explicitly remove a socket from its epoll set using `EPOLL_CTL_DEL` *before* closing it.<br> As on Linux, closed sockets are automatically removed from the epoll set, but wepoll may not be able to detect that a socket was closed until the next call to [`epoll_wait()`](#epoll_wait). * [Linux man page][man epoll_ctl] ### epoll_wait ```c int epoll_wait(HANDLE ephnd, struct epoll_event* events, int maxevents, int timeout); ``` * Receive socket events from an epoll port. * `events` should point to a caller-allocated array of [`epoll_event`](#struct-epoll_event) structs, which will receive the reported events. * `maxevents` is the maximum number of events that will be written to the `events` array, and must be greater than zero. * `timeout` specifies whether to block when no events are immediately available. - `<0` block indefinitely - `0` report any events that are already waiting, but don't block - `≥1` block for at most N milliseconds * Return value: - `-1` an error occurred - `0` timed out without any events to report - `≥1` the number of events stored in the `events` buffer * [Linux man page][man epoll_wait] ### struct epoll_event ```c typedef union epoll_data { void* ptr; int fd; uint32_t u32; uint64_t u64; SOCKET sock; /* Windows specific */ HANDLE hnd; /* Windows specific */ } epoll_data_t; ``` ```c struct epoll_event { uint32_t events; /* Epoll events and flags */ epoll_data_t data; /* User data variable */ }; ``` * The `events` field is a bit mask containing the events being monitored/reported, and optional flags.<br> Flags are accepted by [`epoll_ctl()`](#epoll_ctl), but they are not reported back by [`epoll_wait()`](#epoll_wait). * The `data` field can be used to associate application-specific information with a socket; its value will be returned unmodified by [`epoll_wait()`](#epoll_wait). * [Linux man page][man epoll_ctl] | Event | Description | |---------------|----------------------------------------------------------------------| | `EPOLLIN` | incoming data available, or incoming connection ready to be accepted | | `EPOLLOUT` | ready to send data, or outgoing connection successfully established | | `EPOLLRDHUP` | remote peer initiated graceful socket shutdown | | `EPOLLPRI` | out-of-band data available for reading | | `EPOLLERR` | socket error¹ | | `EPOLLHUP` | socket hang-up¹ | | `EPOLLRDNORM` | same as `EPOLLIN` | | `EPOLLRDBAND` | same as `EPOLLPRI` | | `EPOLLWRNORM` | same as `EPOLLOUT` | | `EPOLLWRBAND` | same as `EPOLLOUT` | | `EPOLLMSG` | never reported | | Flag | Description | |------------------|---------------------------| | `EPOLLONESHOT` | report event(s) only once | | `EPOLLET` | not supported by wepoll | | `EPOLLEXCLUSIVE` | not supported by wepoll | | `EPOLLWAKEUP` | not supported by wepoll | ¹: the `EPOLLERR` and `EPOLLHUP` events may always be reported by [`epoll_wait()`](#epoll_wait), regardless of the event mask that was passed to [`epoll_ctl()`](#epoll_ctl). [ci status badge]: https://ci.appveyor.com/api/projects/status/github/piscisaureus/wepoll?branch=master&svg=true [ci status link]: https://ci.appveyor.com/project/piscisaureus/wepoll/branch/master [dist]: https://github.com/piscisaureus/wepoll/tree/dist [man epoll]: http://man7.org/linux/man-pages/man7/epoll.7.html [man epoll_create]: http://man7.org/linux/man-pages/man2/epoll_create.2.html [man epoll_ctl]: http://man7.org/linux/man-pages/man2/epoll_ctl.2.html [man epoll_wait]: http://man7.org/linux/man-pages/man2/epoll_wait.2.html [msdn accept]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms737526(v=vs.85).aspx [msdn socket]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms740506(v=vs.85).aspx [msdn wsasocket]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms742212(v=vs.85).aspx [select scale]: https://daniel.haxx.se/docs/poll-vs-select.html [wsapoll broken]: https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/ [wepoll.c]: https://github.com/piscisaureus/wepoll/blob/dist/wepoll.c [wepoll.h]: https://github.com/piscisaureus/wepoll/blob/dist/wepoll.h