Reimplement the event queue in event.c using klist.h

 - Add a new macro to klist.h: kl_empty()

   The whole point of abstract data structures is to avoid reimplementing
   common actions. The emptiness test seems to be such an action.

 - Add a new function attribute to func_attr.h: FUNC_ATTR_UNUSED

   Some of the many functions created by the macros in klist.h may end up not
   being used. Unused functions cause compilation errors as we compile with
   -Werror. To mark those functions as possibly unused we can use the
   FUNC_ATTR_UNUSED now.

 - Pass `Event` by value

   `Event` is such a small struct that I don't think we should allocate heap space
   and pass it by reference. Let's use the stack and memory cache in our favor
   passing it by value.

6 files changed, 34 insertions, 48 deletions

diff --git a/src/func_attr.h b/src/func_attr.h
index 94bab79a97..4275d23ff1 100644
--- a/src/func_attr.h
+++ b/src/func_attr.h
@@ -34,6 +34,7 @@
   #define FUNC_ATTR_CONST __attribute__((const))
   #define FUNC_ATTR_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
   #define FUNC_ATTR_ALWAYS_INLINE __attribute__((always_inline))
+  #define FUNC_ATTR_UNUSED __attribute__((unused))
 
   #ifdef __clang__
     // clang only
@@ -90,6 +91,10 @@
   #define FUNC_ATTR_ALWAYS_INLINE
 #endif
 
+#ifndef FUNC_ATTR_UNUSED
+  #define FUNC_ATTR_UNUSED
+#endif
+
 #ifndef FUNC_ATTR_NONNULL_ALL
   #define FUNC_ATTR_NONNULL_ALL
 #endif
diff --git a/src/lib/klist.h b/src/lib/klist.h
index bb60449915..f8b16ea9fa 100644
--- a/src/lib/klist.h
+++ b/src/lib/klist.h
@@ -26,8 +26,10 @@
 #ifndef _AC_KLIST_H
 #define _AC_KLIST_H
 
+#include <stdbool.h>
 #include <stdlib.h>
 
+#include "func_attr.h"
 #include "memory.h"
 
 #define KMEMPOOL_INIT(name, kmptype_t, kmpfree_f)                       \
@@ -84,6 +86,8 @@
         kl->head->next = 0;                                             \
         return kl;                                                      \
     }                                                                   \
+    static inline void kl_destroy_##name(kl_##name##_t *kl)             \
+        FUNC_ATTR_UNUSED;                                               \
     static inline void kl_destroy_##name(kl_##name##_t *kl) {           \
         kl1_##name *p;                                                  \
         for (p = kl->head; p != kl->tail; p = p->next)                  \
@@ -119,5 +123,6 @@
 #define kl_destroy(name, kl) kl_destroy_##name(kl)
 #define kl_pushp(name, kl) kl_pushp_##name(kl)
 #define kl_shift(name, kl, d) kl_shift_##name(kl, d)
+#define kl_empty(kl) ((kl)->size == 0)
 
 #endif
diff --git a/src/os/event.c b/src/os/event.c
index fe06ff4581..dd8d6d9bdd 100644
--- a/src/os/event.c
+++ b/src/os/event.c
@@ -4,6 +4,7 @@
 
 #include <uv.h>
 
+#include "lib/klist.h"
 #include "os/event.h"
 #include "os/input.h"
 #include "os/signal.h"
@@ -11,22 +12,22 @@
 #include "memory.h"
 #include "misc2.h"
 
-typedef struct EventNode {
-  Event *event;
-  struct EventNode *next;
-} EventNode;
+// event.data will be cleaned up after the event is processed
+#define _destroy_event(x)  // do nothing
+KLIST_INIT(Event, Event, _destroy_event)
 
-static EventNode *head, *tail;
+static klist_t(Event) *event_queue;
 static uv_timer_t timer;
 static uv_prepare_t timer_prepare;
 static bool poll_uv_loop(int ms);
 static void process_all_events(void);
-static bool has_pending_events(void);
 static void timer_cb(uv_timer_t *handle, int);
 static void timer_prepare_cb(uv_prepare_t *, int);
 
 void event_init()
 {
+  // Initialize the event queue
+  event_queue = kl_init(Event);
   // Initialize input events
   input_init();
   // Timer to wake the event loop if a timeout argument is passed to
@@ -72,50 +73,27 @@ bool event_poll(int32_t ms)
 }
 
 // Push an event to the queue
-void event_push(Event *event)
+void event_push(Event event)
 {
-  EventNode *node = (EventNode *)xmalloc(sizeof(EventNode));
-  node->event = event;
-  node->next = NULL;
-
-  if (head == NULL) {
-    head = node;
-  } else {
-    tail->next = node;
-  }
-
-  tail = node;
+  *kl_pushp(Event, event_queue) = event;
 }
 
 // Runs the appropriate action for each queued event
 static void process_all_events()
 {
-  EventNode *next;
-  Event *event;
+  Event event;
 
-  while (has_pending_events()) {
-    next = head->next;
-    event = head->event;
-    free(head);
-    head = next;
-
-    switch (event->type) {
+  while (kl_shift(Event, event_queue, &event) == 0) {
+    switch (event.type) {
       case kEventSignal:
         signal_handle(event);
         break;
       default:
         abort();
     }
-
   }
 }
 
-// Checks if there are queued events
-bool has_pending_events()
-{
-  return head != NULL;
-}
-
 // Wait for some event
 static bool poll_uv_loop(int32_t ms)
 {
@@ -150,7 +128,7 @@ static bool poll_uv_loop(int32_t ms)
   } while (
       // Continue running if ...
       !input_ready() && // we have no input
-      !has_pending_events() && // no events are waiting to be processed
+      kl_empty(event_queue) && // no events are waiting to be processed
       run_mode != UV_RUN_NOWAIT && // ms != 0
       !timed_out  // we didn't get a timeout
       );
@@ -162,7 +140,7 @@ static bool poll_uv_loop(int32_t ms)
     uv_timer_stop(&timer);
   }
 
-  return input_ready() || has_pending_events();
+  return input_ready() || !kl_empty(event_queue);
 }
 
 // Set a flag in the `event_poll` loop for signaling of a timeout
diff --git a/src/os/event.h b/src/os/event.h
index fe846695e5..2470add1cf 100644
--- a/src/os/event.h
+++ b/src/os/event.h
@@ -15,7 +15,7 @@ typedef struct {
 
 void event_init(void);
 bool event_poll(int32_t ms);
-void event_push(Event *event);
+void event_push(Event event);
 
 #endif  // NEOVIM_OS_EVENT_H
 
diff --git a/src/os/signal.c b/src/os/signal.c
index 2ac31060aa..503269208d 100644
--- a/src/os/signal.c
+++ b/src/os/signal.c
@@ -67,12 +67,11 @@ void signal_accept_deadly()
   rejecting_deadly = false;
 }
 
-void signal_handle(Event *event)
+void signal_handle(Event event)
 {
-  int signum = *(int *)event->data;
+  int signum = *(int *)event.data;
 
-  free(event->data);
-  free(event);
+  free(event.data);
 
   switch (signum) {
     case SIGINT:
@@ -148,8 +147,6 @@ static void deadly_signal(int signum)
 
 static void signal_cb(uv_signal_t *handle, int signum)
 {
-  Event *event;
-
   if (rejecting_deadly) {
     if (signum == SIGINT) {
       got_int = true;
@@ -158,9 +155,10 @@ static void signal_cb(uv_signal_t *handle, int signum)
     return;
   } 
 
-  event = (Event *)xmalloc(sizeof(Event));
-  event->type = kEventSignal;
-  event->data = xmalloc(sizeof(int));
-  *(int *)event->data = signum;
+  Event event = {
+    .type = kEventSignal,
+    .data = xmalloc(sizeof(int))
+  };
+  *(int *)event.data = signum;
   event_push(event);
 }
diff --git a/src/os/signal.h b/src/os/signal.h
index a5247742db..4507bea26b 100644
--- a/src/os/signal.h
+++ b/src/os/signal.h
@@ -7,7 +7,7 @@ void signal_init(void);
 void signal_stop(void);
 void signal_accept_deadly(void);
 void signal_reject_deadly(void);
-void signal_handle(Event *event);
+void signal_handle(Event event);
 
 #endif