state: throttle batched event processing when input is available

before, calling vim.schedule() from inside an event would execute
the scheduled callback immediately after this event without
checking for user input in between. Break event processing
whenever user input or an interrupt is available.

1 files changed, 16 insertions, 4 deletions

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;
 }