[GTK] Speedup TreeItem retrieval by removing redundant iterations #882

TreeItem and Tree have been checking indexes for bounds during indexed
access and traversal. Such checks are slow as node size computation is
an O(N) operation.

As Tree already does iteration when retrieving a TreeItem by its index,
and such iteration detects out-of-bounds problems, preliminary model
bounds check is redundant. Also, bounds check is avoidable during
iteration over a node - instead of an index, GTK iterator applies
directly.

Performance improvement proved by running
org.eclipse.swt.tests.junit.performance.Test_org_eclipse_swt_widgets_Tree.jfaceReveal().

In test jfaceReveal[Shape: STAR, virtual: true]:
10_000 elements: 501_378_662ns -> 218_583_468ns
100_000 elements: 52_781_899_817ns -> 20_872_245_796ns (-60%)

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java

@@ -14,6 +14,8 @@
 package org.eclipse.swt.widgets;
 
 
+import java.util.*;
+
 import org.eclipse.swt.*;
 import org.eclipse.swt.events.*;
 import org.eclipse.swt.graphics.*;
@@ -197,16 +199,10 @@ TreeItem _getItem (long iter) {
 	return items [id];
 }
 
-TreeItem _getItem (long parentIter, int index) {
-	long iter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
-	try {
-		GTK.gtk_tree_model_iter_nth_child (modelHandle, iter, parentIter, index);
-		int id = getId (iter, true);
-		if (items [id] != null) return items [id];
-		return items [id] = new TreeItem (this, parentIter, SWT.NONE, index, iter);
-	} finally {
-		OS.g_free (iter);
-	}
+TreeItem _getItem (long parentIter, long iter, int index) {
+	int id = getId (iter, true);
+	if (items [id] != null) return items [id];
+	return items [id] = new TreeItem (this, parentIter, SWT.NONE, index, iter);
 }
 
 void reallocateIds(int newSize) {
@@ -1748,10 +1744,14 @@ public boolean getHeaderVisible () {
  */
 public TreeItem getItem (int index) {
 	checkWidget();
-	if (!(0 <= index && index < GTK.gtk_tree_model_iter_n_children (modelHandle, 0)))  {
-		error (SWT.ERROR_INVALID_RANGE);
+	if (index < 0) error (SWT.ERROR_INVALID_RANGE);
+	long iter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+	try {
+		if (!GTK.gtk_tree_model_iter_nth_child (modelHandle, iter, 0, index)) error (SWT.ERROR_INVALID_RANGE);
+		return _getItem (0, iter, index);
+	} finally {
+		OS.g_free (iter);
 	}
-	return _getItem (0, index);
 }
 
 /**
@@ -1927,26 +1927,18 @@ int getItemHeightInPixels () {
 }
 
 TreeItem [] getItems (long parent) {
-	int length = GTK.gtk_tree_model_iter_n_children (modelHandle, parent);
-	TreeItem[] result = new TreeItem [length];
-	if (length == 0) return result;
-	if ((style & SWT.VIRTUAL) != 0) {
-		for (int i=0; i<length; i++) {
-			result [i] = _getItem (parent, i);
-		}
-	} else {
-		int i = 0;
-		int[] index = new int [1];
-		long iter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+	ArrayList<TreeItem> result = new ArrayList<> ();
+	long iter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+	try {
 		boolean valid = GTK.gtk_tree_model_iter_children (modelHandle, iter, parent);
 		while (valid) {
-			GTK.gtk_tree_model_get (modelHandle, iter, ID_COLUMN, index, -1);
-			result [i++] = items [index [0]];
+			result.add (_getItem (parent, iter, result.size ()));
 			valid = GTK.gtk_tree_model_iter_next (modelHandle, iter);
 		}
+	} finally {
 		OS.g_free (iter);
 	}
-	return result;
+	return result.toArray (new TreeItem [result.size ()]);
 }
 
 /**

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/TreeItem.java

@@ -794,9 +794,14 @@ public TreeItem getItem (int index) {
 	checkWidget();
 	if (index < 0) error (SWT.ERROR_INVALID_RANGE);
 	if (!parent.checkData (this)) error (SWT.ERROR_WIDGET_DISPOSED);
-	int itemCount = GTK.gtk_tree_model_iter_n_children (parent.modelHandle, handle);
-	if (index >= itemCount)  error (SWT.ERROR_INVALID_RANGE);
-	return  parent._getItem (handle, index);
+
+	long iter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+	try {
+		if (!GTK.gtk_tree_model_iter_nth_child (parent.modelHandle, iter, handle, index)) error (SWT.ERROR_INVALID_RANGE);
+		return parent._getItem (handle, iter, index);
+	} finally {
+		OS.g_free (iter);
+	}
 }
 
 /**

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_TreeItem.java

@@ -1174,6 +1174,15 @@ public void test_setTextILjava_lang_String(){
 
 }
 
+@Test
+public void test_removeAll() {
+	TreeItem item = new TreeItem(treeItem, SWT.NONE);
+	assertEquals(1, treeItem.getItemCount());
+	treeItem.removeAll();
+	assertEquals(0, treeItem.getItemCount());
+	assertTrue(item.isDisposed());
+}
+
 /* custom */
 TreeItem treeItem;
 Tree tree;

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/performance/Test_org_eclipse_swt_widgets_Tree.java

@@ -210,6 +210,18 @@ public void secondTraverse() {
 		});
 	}
 
+	@Test
+	public void dispose() {
+		assertMaximumDegree(1.2, n -> {
+			Tree tree = buildSubject(n, this::initializeItem);
+			breadthFirstTraverse(tree, item -> {
+				item.setExpanded(true);
+			});
+			return measureNanos(() -> tree.dispose());
+		});
+	}
+
+
 	@Test
 	public void getForeground() {
 		assertMaximumDegree(1.2, n -> {