event: Refactor async event processing

- Improve the implementation of deferred/immediate events.
- Use the new queue module to change how/when events are queued/processed by
  giving a private queue to each emitter.
- Immediate events(which only exist to break uv_run recursion) are now
  represented in the `loop->fast_events` queue.
- Events pushed to child queues are propagated to the event loop main queue and
  processed as K_EVENT keys.

src/nvim/event/loop.c

@@ -1,3 +1,4 @@
+#include <stdarg.h>
 #include <stdint.h>
 
 #include <uv.h>
@@ -9,15 +10,20 @@
 # include "event/loop.c.generated.h"
 #endif
 
+typedef struct idle_event {
+  uv_idle_t idle;
+  Event event;
+} IdleEvent;
+
 
 void loop_init(Loop *loop, void *data)
 {
   uv_loop_init(&loop->uv);
   loop->uv.data = loop;
-  loop->deferred_events = kl_init(Event);
-  loop->immediate_events = kl_init(Event);
   loop->children = kl_init(WatcherPtr);
   loop->children_stop_requests = 0;
+  loop->events = queue_new_parent(on_put, loop);
+  loop->fast_events = queue_new_child(loop->events);
   uv_signal_init(&loop->uv, &loop->children_watcher);
   uv_timer_init(&loop->uv, &loop->children_kill_timer);
   uv_timer_init(&loop->uv, &loop->poll_timer);
@@ -50,29 +56,20 @@ void loop_poll_events(Loop *loop, int ms)
   }
 
   recursive--;  // Can re-enter uv_run now
-  process_events_from(loop->immediate_events);
+  queue_process_events(loop->fast_events);
 }
 
-
-// Queue an event
-void loop_push_event(Loop *loop, Event event, bool deferred)
+static void on_put(Queue *queue, void *data)
 {
+  Loop *loop = data;
   // Sometimes libuv will run pending callbacks(timer for example) before
   // blocking for a poll. If this happens and the callback pushes a event to one
   // of the queues, the event would only be processed after the poll
   // returns(user hits a key for example). To avoid this scenario, we call
   // uv_stop when a event is enqueued.
   uv_stop(&loop->uv);
-  kl_push(Event, deferred ? loop->deferred_events : loop->immediate_events,
-      event);
 }
 
-void loop_process_event(Loop *loop)
-{
-  process_events_from(loop->deferred_events);
-}
-
-
 void loop_close(Loop *loop)
 {
   uv_close((uv_handle_t *)&loop->children_watcher, NULL);
@@ -83,20 +80,6 @@ void loop_close(Loop *loop)
   } while (uv_loop_close(&loop->uv));
 }
 
-void loop_process_all_events(Loop *loop)
-{
-  process_events_from(loop->immediate_events);
-  process_events_from(loop->deferred_events);
-}
-
-static void process_events_from(klist_t(Event) *queue)
-{
-  while (!kl_empty(queue)) {
-    Event event = kl_shift(Event, queue);
-    event.handler(event);
-  }
-}
-
 static void timer_cb(uv_timer_t *handle)
 {
 }