rb_wait_for_single_fd() should probably be used instead of rb_thread_fd_select()

[eregon]

I've noticed this gem is using rb_thread_fd_select() in

hiredis-rb/ext/hiredis_ext/connection.c

Line 94 in d62cb77

#define _thread_fd_select(n, r, w, e, t) rb_thread_fd_select(n, r, w, e, t)

And it's used by

hiredis-rb/ext/hiredis_ext/connection.c

Line 126 in d62cb77

if (_thread_fd_select(fd + 1, &fds, NULL, NULL, toptr) < 0) {

and

hiredis-rb/ext/hiredis_ext/connection.c

Line 156 in d62cb77

if (_thread_fd_select(fd + 1, NULL, &fds, NULL, toptr) < 0) {

to wait for a single file descriptor, either read or write.

rb_thread_fd_select() uses select(2) internally which is rather inefficient, especially with a large number of open file descriptors.
So int rb_wait_for_single_fd(int fd, int events, struct timeval *tv); seems a better fit there, and that uses poll() internally which is much more efficient.

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As Ruby APIs there is also IO#wait_readable and IO#wait_writable. That's probably less easy to use from C as it takes a Float and not a struct timeval for the timeout.

[eregon]

Also select() seems limited to 1024 descriptors on Linux, so if fd happens to be higher it might just not work.