7 files changed, 50 insertions, 9 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 53717229f6..68c7438ea3 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -1024,7 +1024,7 @@ static int insert_handle_key(InsertState *s)
     break;
 
   case K_EVENT:       // some event
-    multiqueue_process_events(main_loop.events);
+    state_handle_k_event();
     goto check_pum;
 
   case K_COMMAND:       // some command
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 8c8e0d568b..60229e1ebc 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -3029,10 +3029,11 @@ static void f_getchar(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 
     if (argvars[0].v_type == VAR_UNKNOWN) {
       // getchar(): blocking wait.
+      // TODO(bfredl): deduplicate shared logic with state_enter ?
       if (!(char_avail() || using_script() || input_available())) {
         (void)os_inchar(NULL, 0, -1, 0, main_loop.events);
         if (!multiqueue_empty(main_loop.events)) {
-          multiqueue_process_events(main_loop.events);
+          state_handle_k_event();
           continue;
         }
       }
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index d470bfb418..5979f4d3a0 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -935,7 +935,7 @@ static int command_line_execute(VimState *state, int key)
 
   if (s->c == K_EVENT || s->c == K_COMMAND) {
     if (s->c == K_EVENT) {
-      multiqueue_process_events(main_loop.events);
+      state_handle_k_event();
     } else {
       do_cmdline(NULL, getcmdkeycmd, NULL, DOCMD_NOWAIT);
     }
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 4d8b11f832..0b4e2e1f23 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -8103,7 +8103,7 @@ static void nv_event(cmdarg_T *cap)
   // lists or dicts being used.
   may_garbage_collect = false;
   bool may_restart = (restart_edit != 0);
-  multiqueue_process_events(main_loop.events);
+  state_handle_k_event();
   finish_op = false;
   if (may_restart) {
     // Tricky: if restart_edit was set before the handler we are in ctrl-o mode,
diff --git a/src/nvim/os/input.c b/src/nvim/os/input.c
index 9d6518841a..eca245650a 100644
--- a/src/nvim/os/input.c
+++ b/src/nvim/os/input.c
@@ -159,16 +159,28 @@ bool os_char_avail(void)
   return inbuf_poll(0, NULL) == kInputAvail;
 }
 
-// Check for CTRL-C typed by reading all available characters.
+/// Poll for fast events. `got_int` will be set to `true` if CTRL-C was typed.
+///
+/// This invokes a full libuv loop iteration which can be quite costly.
+/// Prefer `line_breakcheck()` if called in a busy inner loop.
+///
+/// Caller must at least check `got_int` before calling this function again.
+/// checking for other low-level input state like `input_available()` might
+/// also be relevant (i e to throttle idle processing when user input is
+/// available)
 void os_breakcheck(void)
 {
+  if (got_int) {
+    return;
+  }
+
   int save_us = updating_screen;
   // We do not want screen_resize() to redraw here.
+  // TODO(bfredl): we are already special casing redraw events, is this
+  // hack still needed?
   updating_screen++;
 
-  if (!got_int) {
-    loop_poll_events(&main_loop, 0);
-  }
+  loop_poll_events(&main_loop, 0);
 
   updating_screen = save_us;
 }
diff --git a/src/nvim/state.c b/src/nvim/state.c
index b195c1d96b..a3c74789d1 100644
--- a/src/nvim/state.c
+++ b/src/nvim/state.c
@@ -75,6 +75,34 @@ getkey:
   }
 }
 
+/// process events on main_loop, but interrupt if input is available
+///
+/// This should be used to handle K_EVENT in states accepting input
+/// otherwise bursts of events can block break checking indefinitely.
+void state_handle_k_event(void)
+{
+  while (true) {
+    Event event = multiqueue_get(main_loop.events);
+    if (event.handler) {
+      event.handler(event.argv);
+    }
+
+    if (multiqueue_empty(main_loop.events)) {
+      // don't breakcheck before return, caller should return to main-loop
+      // and handle input already.
+      return;
+    }
+
+    // TODO(bfredl): as an further micro-optimization, we could check whether
+    // event.handler already checked input.
+    os_breakcheck();
+    if (input_available() || got_int) {
+      return;
+    }
+  }
+}
+
+
 /// Return true if in the current mode we need to use virtual.
 bool virtual_active(void)
 {
diff --git a/src/nvim/terminal.c b/src/nvim/terminal.c
index 642c443318..f6995cddb6 100644
--- a/src/nvim/terminal.c
+++ b/src/nvim/terminal.c
@@ -457,7 +457,7 @@ static int terminal_execute(VimState *state, int key)
     case K_EVENT:
       // We cannot let an event free the terminal yet. It is still needed.
       s->term->refcount++;
-      multiqueue_process_events(main_loop.events);
+      state_handle_k_event();
       s->term->refcount--;
       if (s->term->buf_handle == 0) {
         s->close = true;