Use sparse cache instead of full getItems() eclipse-platform#882

basilevs · Nov 12, 2023 · a7a0685 · a7a0685
1 parent eaa5e60
commit a7a0685
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Showing 3 changed files with 27 additions and 13 deletions.
diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/TreeItem.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/TreeItem.java
@@ -794,12 +794,8 @@ public int getItemCount () {
 public TreeItem getItem (int index) {
 	checkWidget();
 	if (index < 0) error (SWT.ERROR_INVALID_RANGE);
-	// It may seem that requesting GTK for an item by index is quicker,
-	// but it has O(N) execution time and cache of all children amortizes that.
-	// This avoids quadratic execution time on traversals
-	TreeItem[] items = getCache().getItems();
-	if (index >= items.length)  error (SWT.ERROR_INVALID_RANGE);
-	return items[index];
+	if (index >= getCache().getItemCount())  error (SWT.ERROR_INVALID_RANGE);
+	return getCache().getItem(index);
 }
 
 /**

diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/TreeItemCache.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/TreeItemCache.java
@@ -21,7 +21,8 @@
  * @since 3.125**/
 class TreeItemCache {
 	final TreeItem owner;
-	private TreeItem[] children;
+	private TreeItem[] allChildren;
+	private final ArrayList<TreeItem> sparseChildren = new ArrayList<>();
 	private int itemCount = -1;
 
 	TreeItemCache(TreeItem owner) {
@@ -35,16 +36,34 @@ int getItemCount() {
 		return itemCount;
 	}
 
+	TreeItem getItem(int index) {
+		if (sparseChildren.size() > index && sparseChildren.get(index) != null) {
+			return sparseChildren.get(index);
+		} else {
+			int newSize = Math.max(index + 1, itemCount);
+			int extraSize = newSize - sparseChildren.size();
+			if (extraSize > 0) {
+				sparseChildren.addAll(Collections.nCopies(extraSize, null));
+			}
+			TreeItem result = owner.parent._getItem(owner.handle, index);
+			sparseChildren.set(index, result);
+			return result;
+		}
+	}
+
 	TreeItem[] getItems() {
-		if (children == null) {
-			children = owner.parent.getItems(owner.handle);
-			itemCount = children.length;
+		if (allChildren == null) {
+			allChildren = owner.parent.getItems(owner.handle);
+			sparseChildren.clear();
+			sparseChildren.addAll(Arrays.asList(allChildren));
+			itemCount = allChildren.length;
 		}
-		return children;
+		return allChildren;
 	}
 
 	public void reset() {
 		itemCount = -1;
-		children = null;
+		allChildren = null;
+		sparseChildren.clear();
 	}
 }
diff --git a/....swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Tree.java b/....swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Tree.java
@@ -1261,7 +1261,6 @@ void depthFirstTraverse(TreeItem parent) {
  */
 private double measureNanos(Runnable operation) {
 	// warmup and calibration - we measure, how many iterations we can approximately do in a second
-
 	long warmupStop = System.nanoTime() + TimeUnit.SECONDS.toNanos(1);
 	long iterationCount = 0;
 	while (System.nanoTime() < warmupStop) {