Commit: patch 9.2.0274: BSU/ESU are output directly to the terminal

[Christian Brabandt]

patch 9.2.0274: BSU/ESU are output directly to the terminal

Commit: https://github.com/vim/vim/commit/309332a32e02d934540c1d35e38779c1b3570d48
Author: Yasuhiro Matsumoto <matt...@gmail.com>
Date: Tue Mar 31 16:34:23 2026 +0000

patch 9.2.0274: BSU/ESU are output directly to the terminal

Problem: BSU/ESU are output directly to the terminal
Solution: Route them through out_buf() and flush the output directly,
increase the OUT_SIZE terminal buffer (Yasuhiro Matsumoto)

Route synchronized-output control sequences through out_buf and flush
explicitly at protocol boundaries, instead of forcing BSU/ESU through
ui_write() directly.

Also increase the terminal output buffer from 2047 to 8191 bytes so
large redraws are emitted in fewer writes.

The important guarantee here is terminal-visible ordering: BSU must
reach the terminal before the batched redraw bytes, ESU must reach the
terminal after them, and FLUSH must emit ESU and BSU together, then
flush immediately.

Benchmark: PTY redraw workload with TERM=xterm-256color, long wrapped
lines, cursorline, listchars, horizontal scrolling, and repeated redraw!.

write syscalls: 8514 -> 5094 (-40.2%)
wall time: 0.568s -> 0.495s (-12.9%) on valid runs in this environment

closes: #19862

Signed-off-by: Yasuhiro Matsumoto <matt...@gmail.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/src/term.c b/src/term.c
index 64eff178f..bdf81bd61 100644
--- a/src/term.c
+++ b/src/term.c
@@ -2807,7 +2807,7 @@ termcapinit(char_u *name)
/*
* The number of calls to ui_write is reduced by using "out_buf".
*/
-#define OUT_SIZE 2047
+#define OUT_SIZE 8191

// add one to allow mch_write() in os_win32.c to append a NUL
static char_u out_buf[OUT_SIZE + 1];
@@ -8059,12 +8059,19 @@ term_set_win_resize(bool state)
* Enable or disable synchronized output if possible. Specification can be found
* here:
* https://github.com/contour-terminal/vt-extensions/blob/master/synchronized-output.md
+ *
+ * BSU/ESU do not need to bypass out_buf and go straight to ui_write().
+ * What matters is the order in which they reach the terminal:
+ * - BSU must be emitted before the batched redraw bytes.
+ * - ESU must be emitted after those redraw bytes.
+ * - A FLUSH must emit ESU and BSU together, then flush immediately.
+ * As long as out_flush() is done at those boundaries, putting BSU/ESU in
+ * out_buf reduces small writes without changing the observable protocol.
*/
void
term_set_sync_output(int flags)
{
bool allowed;
- char_u *str;
#ifdef FEAT_GUI
bool in_gui = gui.in_use;
#else
@@ -8075,12 +8082,13 @@ term_set_sync_output(int flags)

if (flags & TERM_SYNC_OUTPUT_FLUSH)
{
- // Tell terminal to display screen contents
+ // Tell terminal to display screen contents, then resume batching.
if (allowed && !in_gui && sync_output_state > 0 && *T_ESU != NUL &&
*T_BSU != NUL)
{
- ui_write((char_u *)T_ESU, (int)STRLEN(T_ESU), true);
- ui_write((char_u *)T_BSU, (int)STRLEN(T_BSU), true);
+ out_str_nf(T_ESU);
+ out_str_nf(T_BSU);
+ out_flush();
}
return;
}
@@ -8090,7 +8098,8 @@ term_set_sync_output(int flags)
{
if (sync_output_state > 0 && *T_ESU != NUL)
{
- ui_write((char_u *)T_ESU, (int)STRLEN(T_ESU), true);
+ out_str_nf(T_ESU);
+ out_flush();
sync_output_state = 0;
}
return;
@@ -8105,7 +8114,7 @@ term_set_sync_output(int flags)
{
if (sync_output_state++ > 0)
return;
- str = T_BSU;
+ out_str_nf(T_BSU);
}
else if (flags & TERM_SYNC_OUTPUT_DISABLE)
{
@@ -8115,15 +8124,12 @@ term_set_sync_output(int flags)
// all drawing output is sent to the terminal within the
// BSU..ESU window. Without this, the drawing data remaining in
// out_buf would be sent after ESU, outside the sync batch.
+ out_str_nf(T_ESU);
out_flush();
- str = T_ESU;
}
else
{
siemsg("Unknown sync output value %d", flags);
return;
}
-
- // Directly write to terminal instead of using output buffer
- ui_write((char_u *)str, (int)STRLEN(str), true);
}
diff --git a/src/version.c b/src/version.c
index 35702fe0c..1e3ed45ed 100644
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 274,
/**/
273,
/**/