Add kqueue notifications for macOS stat watchers

ext/cool.io/stat_watcher.c

@@ -33,9 +33,8 @@ static void Coolio_StatWatcher_libev_callback(struct ev_loop *ev_loop, struct ev
 static void Coolio_StatWatcher_dispatch_callback(VALUE self, int revents);
 
 /*
- * Coolio::StatWatcher lets you create either one-shot or periodic stats which
- * run within Coolio's event loop.  It's useful for creating timeouts or
- * events which fire periodically.
+ * Coolio::StatWatcher monitors a path and calls on_change when its stat
+ * attributes change.
  **/
 void Init_coolio_stat_watcher()
 {
@@ -77,10 +76,18 @@ void Init_coolio_stat_watcher()
  * specified how often in seconds the path should be polled for changes.
  * Setting interval to zero uses an "automatic" value (typically around 5
  * seconds) which optimizes performance.  Otherwise, values less than
- * 0.1 are not particularly meaningful.  Where available (on Linux and Windows),
- * high performance file monitoring interfaces are used.  On Windows, polling
- * remains necessary because notification timing is not guaranteed.  An attached
- * Windows watcher may also prevent renaming an ancestor directory until detached.
+ * 0.1 are not particularly meaningful.  Where available (on Linux, macOS and
+ * Windows), high performance file monitoring interfaces are used.  On macOS
+ * and Windows, polling remains enabled for changes native notifications may
+ * miss.  An attached Windows watcher may also prevent renaming an ancestor
+ * directory until detached.
+ *
+ * On macOS, each registered watcher uses one file descriptor for the path or
+ * an ancestor directory, plus one shared kqueue descriptor per loop. If the
+ * descriptor limit is reached, watchers fall back to polling.
+ *
+ * On macOS, construct the loop with :fork_check => true when continuing to
+ * use attached watchers in a forked child.
  */
 static VALUE Coolio_StatWatcher_initialize(int argc, VALUE *argv, VALUE self)
 {

ext/libev/ev.c

@@ -342,6 +342,14 @@
 # endif
 #endif
 
+#ifndef EV_USE_KQUEUE_STAT
+# if EV_USE_KQUEUE && EV_STAT_ENABLE && defined __APPLE__ && defined __MACH__
+#  define EV_USE_KQUEUE_STAT 1
+# else
+#  define EV_USE_KQUEUE_STAT 0
+# endif
+#endif
+
 #ifndef EV_PID_HASHSIZE
 # define EV_PID_HASHSIZE EV_FEATURE_DATA ? 16 : 1
 #endif
@@ -1863,6 +1871,10 @@ typedef struct
 #if defined(_WIN32) && EV_STAT_ENABLE && EV_ASYNC_ENABLE
 static void win32_fs_destroy (EV_P);
 #endif
+#if EV_USE_KQUEUE_STAT
+static void kq_stat_fork (EV_P);
+static void kq_stat_destroy (EV_P);
+#endif
 
 #if EV_FEATURE_API
 # define EV_RELEASE_CB if (expect_false (release_cb)) release_cb (EV_A)
@@ -2937,6 +2949,10 @@ loop_init (EV_P_ unsigned int flags) EV_THROW
       win32_fs          = 0;
       win32_fs_disabled = (flags & EVFLAG_NOINOTIFY) != 0;
 #endif
+#if EV_USE_KQUEUE_STAT
+      kq_stat          = 0;
+      kq_stat_disabled = (flags & EVFLAG_NOINOTIFY) != 0;
+#endif
 #if EV_USE_INOTIFY
       fs_fd              = flags & EVFLAG_NOINOTIFY ? -1 : -2;
 #endif
@@ -3008,6 +3024,9 @@ ev_loop_destroy (EV_P)
 #if defined(_WIN32) && EV_STAT_ENABLE && EV_ASYNC_ENABLE
   win32_fs_destroy (EV_A);
 #endif
+#if EV_USE_KQUEUE_STAT
+  kq_stat_destroy (EV_A);
+#endif
 
   if (ev_is_active (&pipe_w))
     {
@@ -3110,6 +3129,9 @@ loop_fork (EV_P)
 #if EV_USE_INOTIFY
   infy_fork (EV_A);
 #endif
+#if EV_USE_KQUEUE_STAT
+  kq_stat_fork (EV_A);
+#endif
 
 #if EV_SIGNAL_ENABLE || EV_ASYNC_ENABLE
   if (ev_is_active (&pipe_w) && postfork != 2)
@@ -4366,6 +4388,9 @@ noinline static void stat_timer_cb (EV_P_ ev_timer *w_, int revents);
 #if defined(_WIN32) && EV_ASYNC_ENABLE
 # include "ev_win32_stat.c"
 #endif
+#if EV_USE_KQUEUE_STAT
+# include "ev_kqueue_stat.c"
+#endif
 
 #if EV_USE_INOTIFY
 
@@ -4648,6 +4673,10 @@ stat_timer_cb (EV_P_ ev_timer *w_, int revents)
     win32_fs_add (EV_A_ w, 1); /* retry missing parents or failed directory handles */
 #endif
 
+#if EV_USE_KQUEUE_STAT
+  kq_stat_poll (EV_A_ w, revents);
+#endif
+
   ev_statdata prev = w->attr;
   ev_stat_stat (EV_A_ w);
 
@@ -4685,6 +4714,10 @@ stat_timer_cb (EV_P_ ev_timer *w_, int revents)
           }
       #endif
 
+#if EV_USE_KQUEUE_STAT
+      kq_stat_refresh (EV_A_ w);
+#endif
+
       ev_feed_event (EV_A_ w, EV_STAT);
     }
 }
@@ -4721,6 +4754,9 @@ ev_stat_start (EV_P_ ev_stat *w) EV_THROW
   win32_fs_add (EV_A_ w, 0);
   stat_timer_cb (EV_A_ &w->timer, 0); /* close the stat/registration race */
 #endif
+#if EV_USE_KQUEUE_STAT
+  kq_stat_start (EV_A_ w);
+#endif
 
   EV_FREQUENT_CHECK;
 }
@@ -4737,6 +4773,9 @@ ev_stat_stop (EV_P_ ev_stat *w) EV_THROW
 #if defined(_WIN32) && EV_ASYNC_ENABLE
   win32_fs_del (EV_A_ w);
 #endif
+#if EV_USE_KQUEUE_STAT
+  kq_stat_del (EV_A_ w);
+#endif
 
 #if EV_USE_INOTIFY
   infy_del (EV_A_ w);