tui: "backpressure": Drop messages to avoid flooding.

Closes #1234

multiqueue:
- Implement multiqueue_size()
- Rename MultiQueueItem.parent to MultiQueueItem.parent_item, to avoid confusion
  with MultiQueue.parent.

1 files changed, 7 insertions, 11 deletions

diff --git a/src/nvim/lib/queue.h b/src/nvim/lib/queue.h
index 9fcedf298f..ab9270081e 100644
--- a/src/nvim/lib/queue.h
+++ b/src/nvim/lib/queue.h
@@ -1,3 +1,8 @@
+// Queue implemented by circularly-linked list.
+//
+// Adapted from libuv. Simpler and more efficient than klist.h for implementing
+// queues that support arbitrary insertion/removal.
+//
 // Copyright (c) 2013, Ben Noordhuis <info@bnoordhuis.nl>
 //
 // Permission to use, copy, modify, and/or distribute this software for any
@@ -28,6 +33,8 @@ typedef struct _queue {
 #define QUEUE_DATA(ptr, type, field) \
   ((type *)((char *)(ptr) - offsetof(type, field)))
 
+// Important note: mutating the list while QUEUE_FOREACH is
+// iterating over its elements results in undefined behavior.
 #define QUEUE_FOREACH(q, h) \
   for (  /* NOLINT(readability/braces) */ \
       (q) = (h)->next; (q) != (h); (q) = (q)->next)
@@ -56,17 +63,6 @@ static inline void QUEUE_ADD(QUEUE *const h, QUEUE *const n)
   h->prev->next = h;
 }
 
-static inline void QUEUE_SPLIT(QUEUE *const h, QUEUE *const q, QUEUE *const n)
-  FUNC_ATTR_ALWAYS_INLINE
-{
-  n->prev = h->prev;
-  n->prev->next = n;
-  n->next = q;
-  h->prev = q->prev;
-  h->prev->next = h;
-  q->prev = n;
-}
-
 static inline void QUEUE_INSERT_HEAD(QUEUE *const h, QUEUE *const q)
   FUNC_ATTR_ALWAYS_INLINE
 {