kqueue: Multiple fixes and simplifications

- Stop using a custom thread for listening to kqueue(2) events.  Instead
   call kevent(2) in non blocking mode in a monitor callback.  Under the
   hood poll(2) is used to figure out if new events are available.

 - Do not use a socketpair with a custom protocol requiring 2 supplementary
   context switches per event to commicate between multiple threads.  Calling
   kevent(2), in non blocking mode, to add/remove events is fine from any
   context.

 - Add kqueue(2) events without the EV_ONESHOT flag.  This removes a race
   where some notifications were lost because events had to be re-added for
   every new notification.

 - Get rid of the global hash table and its associated lock and races.  Use
   the 'cookie' argument of kevent(2) to pass the associated descriptor when
   registering an event.

 - Fix _kh_file_appeared_cb() by properly passing a monitor instead of a
   source to g_file_monitor_emit_event().

 - Properly refcount sources.

 - Remove a lot of abstraction making it harder to fix the remaining issues.

https://bugzilla.gnome.org/show_bug.cgi?id=739424

gio/kqueue/kqueue-helper.h

@@ -23,16 +23,31 @@
 #ifndef __KQUEUE_HELPER_H
 #define __KQUEUE_HELPER_H
 
-#include "kqueue-sub.h"
 #include <gio/glocalfilemonitor.h>
 #include <gio/gfilemonitor.h>
 
-gboolean _kh_startup        (void);
-gboolean _kh_add_sub        (kqueue_sub *sub);
-gboolean _kh_cancel_sub     (kqueue_sub *sub);
+#include "dep-list.h"
 
-gboolean _kh_start_watching (kqueue_sub *sub);
+/**
+ * kqueue_sub:
+ * @filename: a name of the file to monitor
+ * @fd: the associated file descriptor (used by kqueue)
+ *
+ * Represents a subscription on a file or directory.
+ */
+typedef struct
+{
+  GLocalFileMonitor   *mon;
+  GFileMonitorSource  *source;
+  gchar*    filename;
+  int       fd;
+  dep_list* deps;
+  int       is_dir;
+} kqueue_sub;
 
-void     _kh_dir_diff       (kqueue_sub *sub, GFileMonitorSource *source);
+gboolean _kqsub_start_watching (kqueue_sub *sub);
+void _kh_dir_diff    (kqueue_sub *sub);
+void _km_add_missing (kqueue_sub *sub);
+void _km_remove      (kqueue_sub *sub);
 
 #endif /* __KQUEUE_HELPER_H */