vim-patch:8.1.0822: peeking and flushing output slows down execution

Problem:    Peeking and flushing output slows down execution.
Solution:   Do not update the mode message when global_busy is set.  Do not
            flush when only peeking for a character. (Ken Takata)
https://github.com/vim/vim/commit/cb574f415486adff645ce384979bfecf27f5be8c

3 files changed, 22 insertions, 9 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index ec424c12da..539418cf09 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -7803,7 +7803,7 @@ static bool ins_esc(long *count, int cmdchar, bool nomove)
   // Otherwise remove the mode message.
   if (reg_recording != 0 || restart_edit != NUL) {
     showmode();
-  } else if (p_smd) {
+  } else if (p_smd && !skip_showmode()) {
     MSG("");
   }
   // Exit Insert mode
diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index 2e2993ed26..eddbdef739 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -2490,8 +2490,10 @@ int inchar(
     }
 
     // Always flush the output characters when getting input characters
-    // from the user.
-    ui_flush();
+    // from the user and not just peeking.
+    if (wait_time == -1L || wait_time > 10L) {
+      ui_flush();
+    }
 
     // Fill up to a third of the buffer, because each character may be
     // tripled below.
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index afabbe6afc..b4b358052b 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -6557,6 +6557,21 @@ void grid_del_lines(ScreenGrid *grid, int row, int line_count, int end, int col,
   return;
 }
 
+// Return true when postponing displaying the mode message: when not redrawing
+// or inside a mapping.
+bool skip_showmode(void)
+{
+  // Call char_avail() only when we are going to show something, because it
+  // takes a bit of time.  redrawing() may also call char_avail_avail().
+  if (global_busy
+      || msg_silent != 0
+      || !redrawing()
+      || (char_avail() && !KeyTyped)) {
+    redraw_cmdline = true;  // show mode later
+    return true;
+  }
+  return false;
+}
 
 // Show the current mode and ruler.
 //
@@ -6588,12 +6603,8 @@ int showmode(void)
                  || restart_edit
                  || VIsual_active));
   if (do_mode || reg_recording != 0) {
-    // Don't show mode right now, when not redrawing or inside a mapping.
-    // Call char_avail() only when we are going to show something, because
-    // it takes a bit of time.
-    if (!redrawing() || (char_avail() && !KeyTyped) || msg_silent != 0) {
-      redraw_cmdline = TRUE;                    /* show mode later */
-      return 0;
+    if (skip_showmode()) {
+      return 0;  // show mode later
     }
 
     nwr_save = need_wait_return;