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SqMod/vendor/ZMQ/external/wepoll/README.md
2021-02-02 19:07:02 +02:00

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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 error<sup>1</sup> |
| `EPOLLHUP` | socket hang-up<sup>1</sup> |
| `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 |
<sup>1</sup>: 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