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

As we already do iteration of O(N) complexity, and it detects
out-of-bounds problems, eliminate redundant model size check computed in
O(N).

Performance improvement is proven 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 -> {