[ruby-core:99602] [Ruby master Feature#17059] epoll as the backend of IO.select on Linux

[dsh0416@gmail.com]

Issue #17059 has been updated by dsh0416 (Delton Ding).


In general, event handling gems like nio4r could provide a similar `select` interface with multiple backends including select, kqueue and epoll support.
On the side of Ruby meta-programming, this part is easy to be implemented, and could provide a much better performance comparing to the default IO.select.
But since Ruby merged the Fiber scheduler recently, the IO.select injection from the core library may be important to provide extra performance.
From the patch, Ruby does use the POSIX `fdset_t` in some platforms, but Ruby also defines its own structs on some other platforms for non-standard select implementation.
Since the `IO.select` has seperated code with macro to use these customized struct. We may also create another macro branch for the epoll compatible implementation.
This is my current idea, and I'm working on implementing this.

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Feature #17059: epoll as the backend of IO.select on Linux
https://bugs.ruby-lang.org/issues/17059#change-87081

* 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)


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