KQueue support for M:N threads

* Allows macOS users to use M:N threads (and technically FreeBSD, though it has not been verified on FreeBSD)

* Include sys/event.h header check for macros, and include sys/event.h when present

* Rename epoll_fd to more generic kq_fd (Kernel event Queue) for use by both epoll and kqueue

* MAP_STACK is not available on macOS so conditionall apply it to mmap flags

* Set fd to close on exec

* Log debug messages specific to kqueue and epoll on creation

* close_invalidate raises an error for the kqueue fd on child process fork. It's unclear rn if that's a bug, or if it's kqueue specific behavior

Use kq with rb_thread_wait_for_single_fd

* Only platforms with `USE_POLL` (linux) had changes applied to take advantage of kernel event queues. It needed to be applied to the `select` so that kqueue could be properly applied

* Clean up kqueue specific code and make sure only flags that were actually set are removed (or an error is raised)

* Also handle kevent specific errnos, since most don't apply from epoll to kqueue

* Use the more platform standard close-on-exec approach of `fcntl` and `FD_CLOEXEC`. The io-event gem uses `ioctl`, but fcntl seems to be the recommended choice. It is also what Go, Bun, and Libuv use

* We're making changes in this file anyways - may as well fix a couple spelling mistakes while here

Make sure FD_CLOEXEC carries over in dup

* Otherwise the kqueue descriptor should have FD_CLOEXEC, but doesn't and fails in assert_close_on_exec

1 files changed, 7 insertions, 0 deletions

diff --git a/process.c b/process.c
index 395c69e08f..3b254ddecb 100644
--- a/process.c
+++ b/process.c
@@ -3354,6 +3354,13 @@ run_exec_dup2(VALUE ary, VALUE tmpbuf, struct rb_execarg *sargp, char *errmsg, s
                 ERRMSG("dup");
                 goto fail;
             }
+            // without this, kqueue timer_th.event_fd fails with a reserved FD did not have close-on-exec
+            //   in #assert_close_on_exec because the FD_CLOEXEC is not dup'd by default
+            if (fd_get_cloexec(pairs[i].oldfd, errmsg, errmsg_buflen)) {
+                if (fd_set_cloexec(extra_fd, errmsg, errmsg_buflen)) {
+                    goto fail;
+                }
+            }
             rb_update_max_fd(extra_fd);
         }
         else {