Issue #17059 has been updated by Eregon (Benoit Daloze).


I'm unclear how using `epoll` can help for the user calling `IO.select`.
With the API of select(), I'd expect `epoll` is no faster than `select()`.

Regarding the Fiber scheduler, then I think new event is needed, calling epoll() instead of select() wouldn't solve anything, right?

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Feature #17059: epoll as the backend of IO.select on Linux
https://bugs.ruby-lang.org/issues/17059#change-87089

* Author: dsh0416 (Delton Ding)
* Status: Open
* Priority: Normal
----------------------------------------
Current Ruby's `IO.select` method calls POSIX `select` API directly. With the new non-blocking scheduler, this may be the bottleneck of the I/O scheduling. For keeping the backward compatibilty of the current `IO.select` methods, a proposal may be to create a "duck" `select` which uses the `epoll_wait` as the backend.

One tricky part is that the `fd_set` described in POSIX is write-only, which means it is impossible to iterate for generating the `epoll_event` argument for `epoll_wait`. But similar to the large-size select situation, we could define our own `rb_fdset_t` struct in this case, and implement the following APIs.

```
void rb_fd_init(rb_fdset_t *);
void rb_fd_term(rb_fdset_t *);
void rb_fd_zero(rb_fdset_t *);
void rb_fd_set(int, rb_fdset_t *);
void rb_fd_clr(int, rb_fdset_t *);
int rb_fd_isset(int, const rb_fdset_t *);
void rb_fd_copy(rb_fdset_t *, const fd_set *, int);
void rb_fd_dup(rb_fdset_t *dst, const rb_fdset_t *src);
int rb_fd_select(int, rb_fdset_t *, rb_fdset_t *, rb_fdset_t *, struct timeval *);
```

TODO:
1. Implement the fd_set with dynamic allocated fds.
2. Implement the epoll with select API.
3. Edit io.c to use the customized fd_set struct.

I'm trying to work on a branch for this. Any suggestions for this?

---Files--------------------------------
epoll.h (3.62 KB)
epoll.h (6.44 KB)


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