Optimize BufferLine.copyFrom sparse map copying

Skip O(cols) _copyCellMapsFrom loop when the source line has no sparse combined/extended map entries (scroll recycle from cached blank line). Copy sparse entries by map keys only when needed. Add CDP profiling script and BufferLine.copyFrom micro-benchmark. Co-authored-by: Daniel Imms <Tyriar@users.noreply.github.com>
2026-06-04 21:05:33 +00:00
parent f3f4dcaf9f
commit 9872be0c29
3 changed files with 222 additions and 4 deletions
@@ -0,0 +1,55 @@
+/**
+ * Copyright (c) 2026 The xterm.js authors. All rights reserved.
+ * @license MIT
+ */
+
+import { perfContext, before, RuntimeCase } from 'xterm-benchmark';
+import { BufferLine } from 'common/buffer/BufferLine';
+import { BufferLineStringCache } from 'common/buffer/BufferLineStringCache';
+import { DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
+import { CellData } from 'common/buffer/CellData';
+import { NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE } from 'common/buffer/Constants';
+
+const ITERATIONS = 500_000;
+const stringCache = new BufferLineStringCache();
+const nullCell = CellData.fromCharData([0, NULL_CELL_CHAR, NULL_CELL_WIDTH, NULL_CELL_CODE]);
+const yCell = CellData.fromCharData([0, 'y', 1, 'y'.charCodeAt(0)]);
+
+function setupScrollRecyclePair(cols: number): { recycled: BufferLine; blank: BufferLine } {
+  const blank = new BufferLine(stringCache, cols, nullCell, false);
+  const recycled = new BufferLine(stringCache, cols, yCell, false);
+  for (let i = 0; i < cols; i++) {
+    recycled.setCellFromCodepoint(i, 'y'.charCodeAt(0), 1, DEFAULT_ATTR_DATA);
+  }
+  return { recycled, blank };
+}
+
+perfContext('BufferLine.copyFrom (scroll recycle)', () => {
+  perfContext('cols=80', () => {
+    let recycled: BufferLine;
+    let blank: BufferLine;
+    before(() => {
+      ({ recycled, blank } = setupScrollRecyclePair(80));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        recycled.copyFrom(blank);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+
+  perfContext('cols=279', () => {
+    let recycled: BufferLine;
+    let blank: BufferLine;
+    before(() => {
+      ({ recycled, blank } = setupScrollRecyclePair(279));
+    });
+    new RuntimeCase('', () => {
+      for (let i = 0; i < ITERATIONS; i++) {
+        recycled.copyFrom(blank);
+      }
+      return { payloadSize: ITERATIONS };
+    }, { fork: false }).showAverageRuntime();
+  });
+});