Daneel
cd16d45584
BUF_CHARS_MODIFF fix — the core performance regression: ensureTextCache checked BUF_MODIFF which font-lock bumps on every redisplay. Each cursor movement in a large file triggered full buffer rebuild. Now uses BUF_CHARS_MODIFF (changes only on char insert/delete).
78 lines
3.4 KiB
Diff
78 lines
3.4 KiB
Diff
From 4b739781a019fd1ad5b6ac1c9c12dc62e2c82ec3 Mon Sep 17 00:00:00 2001
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From: Daneel <daneel@sukany.cz>
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Date: Sun, 1 Mar 2026 04:56:16 +0100
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Subject: [PATCH 10/10] perf: use BUF_CHARS_MODIFF for AX text cache validity
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in ensureTextCache
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The cache validity check in -[EmacsAccessibilityBuffer ensureTextCache]
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used BUF_MODIFF, which is bumped by every text-property change ---
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including face applications by font-lock on each redisplay cycle.
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Since the AX text value contains only characters (no face or property
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data), property-only changes do not affect it. Rebuilding the full
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buffer text on each font-lock pass is O(buffer-size) per redisplay,
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causing progressive slowdown proportional to how far the cursor is
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from the beginning of the file.
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Switch to BUF_CHARS_MODIFF, which is bumped only when characters are
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actually inserted or deleted. This matches the semantic of 'did the
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text change' and is the approach used by WebKit and NSTextView.
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BUF_OVERLAY_MODIFF is intentionally not tracked here (unchanged):
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overlay content is handled by separate announcements in
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postAccessibilityNotificationsForFrame, and including it in this
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check would prevent those announcements from firing.
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---
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src/nsterm.m | 27 ++++++++++++++++++---------
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1 file changed, 18 insertions(+), 9 deletions(-)
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diff --git a/src/nsterm.m b/src/nsterm.m
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index 12c451b..e3f9466 100644
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--- a/src/nsterm.m
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+++ b/src/nsterm.m
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@@ -8148,16 +8148,25 @@ - (void)ensureTextCache
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if (!b)
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return;
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- ptrdiff_t modiff = BUF_MODIFF (b);
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- ptrdiff_t pt = BUF_PT (b);
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- NSUInteger textLen = cachedText ? [cachedText length] : 0;
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- /* Cache validity: track BUF_MODIFF and buffer narrowing.
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+ /* Use BUF_CHARS_MODIFF, not BUF_MODIFF, for cache validity.
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+ BUF_MODIFF is bumped by every text-property change, including
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+ font-lock face applications on every redisplay. AX text contains
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+ only characters, not face data, so property-only changes do not
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+ affect the cached value. Rebuilding the full buffer text on
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+ each font-lock pass is O(buffer-size) per redisplay --- this
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+ causes progressive slowdown when scrolling through large files.
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+ BUF_CHARS_MODIFF is bumped only on actual character insertions
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+ and deletions, matching the semantic of "did the text change".
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+ This is the pattern used by WebKit and NSTextView.
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Do NOT track BUF_OVERLAY_MODIFF here --- overlay text is not
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included in the cached AX text (it is handled separately via
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- explicit announcements). Including overlay_modiff would
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- silently update cachedOverlayModiff and prevent the
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- notification dispatch from detecting overlay changes. */
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- if (cachedText && cachedTextModiff == modiff
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+ explicit announcements in postAccessibilityNotificationsForFrame).
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+ Including overlay_modiff would silently update cachedOverlayModiff
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+ and prevent the notification dispatch from detecting changes. */
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+ ptrdiff_t chars_modiff = BUF_CHARS_MODIFF (b);
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+ ptrdiff_t pt = BUF_PT (b);
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+ NSUInteger textLen = cachedText ? [cachedText length] : 0;
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+ if (cachedText && cachedTextModiff == chars_modiff
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&& cachedTextStart == BUF_BEGV (b)
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&& pt >= cachedTextStart
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&& (textLen == 0
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@@ -8173,7 +8182,7 @@ included in the cached AX text (it is handled separately via
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{
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[cachedText release];
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cachedText = [text retain];
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- cachedTextModiff = modiff;
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+ cachedTextModiff = chars_modiff;
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cachedTextStart = start;
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if (visibleRuns)
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--
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2.43.0
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