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