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Apply UPDATE_DELAY in arrears, not in advance.

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The original aim of the rate limit was to avoid having too many
updates per second. I implemented this by a deferment mechanism: when
any change occurs that makes the terminal want an update, it instead
sets a timer to go off after UPDATE_DELAY (1/50 second), and does the
update at the end of that interval.

Now it's done the other way round: if there has not been an update
within the last UPDATE_DELAY, then we can simply do an update _right
now_, in immediate response to whatever triggered it. And _then_ we
set a timer to track a cooldown period, within which any further
requests for updates will be deferred until the end of the cooldown.

This mechanism should still rate-limit updates, but now the latency in
normal interactive use should be lowered, because terminal updates in
response to keystrokes (which typically arrive separated by more than
UPDATE_DELAY) can now each be enacted as soon as possible after the
triggering keystroke.

This also reverses (in the common case) the slowdown of non-textual
window modifications introduced by the previous commit, in which lots
of them were brought under the umbrella of term_update and therefore
became subject to UPDATE_DELAY. Now they'll only be delayed in
conditions of high traffic, and not in interactive use.
This commit is contained in:
Simon Tatham
2021-02-07 19:59:21 +00:00
parent d74308e90e
commit 334688db81
2 changed files with 35 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

32
terminal.c
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@ -1187,41 +1187,58 @@ static void check_line_size(Terminal *term, termline *line)
static void term_schedule_tblink(Terminal *term);
static void term_schedule_cblink(Terminal *term);
static void term_update_callback(void *ctx);
static void term_timer(void *ctx, unsigned long now)
{
Terminal *term = (Terminal *)ctx;
bool update = false;
if (term->tblink_pending && now == term->next_tblink) {
term->tblinker = !term->tblinker;
term->tblink_pending = false;
term_schedule_tblink(term);
update = true;
term->window_update_pending = true;
}
if (term->cblink_pending && now == term->next_cblink) {
term->cblinker = !term->cblinker;
term->cblink_pending = false;
term_schedule_cblink(term);
update = true;
term->window_update_pending = true;
}
if (term->in_vbell && now == term->vbell_end) {
term->in_vbell = false;
update = true;
term->window_update_pending = true;
}
if (update ||
(term->window_update_pending && now == term->next_update))
if (term->window_update_cooldown &&
now == term->window_update_cooldown_end) {
term->window_update_cooldown = false;
}
if (term->window_update_pending)
term_update_callback(term);
}
static void term_update_callback(void *ctx)
{
Terminal *term = (Terminal *)ctx;
if (!term->window_update_pending)
return;
if (!term->window_update_cooldown) {
term_update(term);
term->window_update_cooldown = true;
term->window_update_cooldown_end = schedule_timer(
UPDATE_DELAY, term_timer, term);
}
}
static void term_schedule_update(Terminal *term)
{
if (!term->window_update_pending) {
term->window_update_pending = true;
term->next_update = schedule_timer(UPDATE_DELAY, term_timer, term);
queue_toplevel_callback(term_update_callback, term);
}
}
@ -1940,6 +1957,7 @@ Terminal *term_init(Conf *myconf, struct unicode_data *ucsdata, TermWin *win)
term->wcFromTo_size = 0;
term->window_update_pending = false;
term->window_update_cooldown = false;
term->bidi_cache_size = 0;
term->pre_bidi_cache = term->post_bidi_cache = NULL;