From 8da6e4144cabdb9bab71d8f8b4ff736f7e9e28bf Mon Sep 17 00:00:00 2001
From: Vasili Gulevich <vasili.gulevich@xored.com>
Date: Tue, 23 Jan 2024 21:34:22 +0000
Subject: [PATCH] [GTK] Fix slowdown in setItemCount()

The slowdown was caused by update of insertion iterator, that was
avoidable when insertion happens at the beginning of GTK model.
---
 .../gtk/org/eclipse/swt/widgets/Tree.java     | 49 +++++++++----------
 .../gtk/org/eclipse/swt/widgets/TreeItem.java |  8 ++-
 2 files changed, 29 insertions(+), 28 deletions(-)

diff --git a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java
index ea8f69239e..99079e99e3 100644
--- a/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java	
+++ b/bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Tree.java	
@@ -3342,42 +3342,37 @@ void _setItemCount (TreeItem parentItem, long parentIter, List<TreeItem> items,
 			if (currentSize - 1 != items.size () ) throw new AssertionError ("Items should cleanup sibling list on disposal");
 		}
 
-		long modificationIter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
-		if (modificationIter == 0) error (SWT.ERROR_NO_HANDLES);
-		try {
-			int oldSize = items.size ();
-			assert GTK.gtk_tree_model_iter_n_children (modelHandle, parentIter) == oldSize;
-			if (items.size () > count) {
-				GTK.gtk_tree_model_iter_nth_child (modelHandle, modificationIter, parentIter, count);
+		int oldSize = items.size ();
+		assert GTK.gtk_tree_model_iter_n_children (modelHandle, parentIter) == oldSize;
+		if (items.size () > count) {
+			long removeIter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+			if (removeIter == 0) error (SWT.ERROR_NO_HANDLES);
+			try {
+				GTK.gtk_tree_model_iter_nth_child (modelHandle, removeIter, parentIter, count);
 				items.subList (count, items.size ()).clear ();
 				long selection = GTK.gtk_tree_view_get_selection (parent.handle);
 				for (int i = count; i < oldSize; i++) {
 					OS.g_signal_handlers_block_matched (selection, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, CHANGED);
-					GTK.gtk_tree_store_remove (modelHandle, modificationIter);
+					GTK.gtk_tree_store_remove (modelHandle, removeIter);
 					OS.g_signal_handlers_unblock_matched (selection, OS.G_SIGNAL_MATCH_DATA, 0, 0, 0, 0, CHANGED);
 				}
-			} else if (items.size () < count) {
-				if (items.size () > 0) {
-					GTK.gtk_tree_model_iter_nth_child (modelHandle, modificationIter, parentIter, oldSize - 1);
-				}
-				items.addAll(Collections.nCopies (count - items.size(), null));
-				long createdIter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
-				if (createdIter == 0) error (SWT.ERROR_NO_HANDLES);
-				try {
-					for (int i = oldSize; i < count; i++) {
-						GTK.gtk_tree_store_insert_after (modelHandle, createdIter, parentIter, i == 0 ? 0 : modificationIter);
-						TreeItem result = new TreeItem (this, parentItem, SWT.NONE, i, createdIter);
-						assert items.get(i) == result : "TreeItem should self-insert into sibling list";
-						C.memmove (modificationIter, createdIter, GTK.GtkTreeIter_sizeof ());
-					}
-				} finally {
-					OS.g_free (createdIter);
+			} finally {
+				OS.g_free (removeIter);
+			}
+		} else if (items.size () < count) {
+			long createdIter = OS.g_malloc (GTK.GtkTreeIter_sizeof ());
+			if (createdIter == 0) error (SWT.ERROR_NO_HANDLES);
+			try {
+				for (int i = oldSize; i < count; i++) {
+					TreeItem result = new TreeItem (this, parentItem, SWT.NONE, oldSize, 0);
+					assert items.get(oldSize) == result : "TreeItem should self-insert into sibling list";
 				}
+			} finally {
+				OS.g_free (createdIter);
 			}
-			assert GTK.gtk_tree_model_iter_n_children (modelHandle, parentIter) == count;
-		} finally {
-			OS.g_free (modificationIter);
 		}
+		assert GTK.gtk_tree_model_iter_n_children (modelHandle, parentIter) == count;
+		assert items.size() == count;
 	} finally {
 		setRedraw(true);
 	}
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
index e5dd0015e4..2b37ef9284 100644
--- 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	
@@ -203,6 +203,10 @@ public TreeItem (TreeItem parentItem, int style, int index) {
 				 */
 				GTK.gtk_tree_store_append (parent.modelHandle, handle, parentIter);
 				siblings.add (this);
+			} else if (siblings.get(index - 1) != null) {
+				TreeItem insertAfterItem = siblings.get(index - 1);
+				GTK.gtk_tree_store_insert_after (parent.modelHandle, handle, parentIter, insertAfterItem.handle);
+				siblings.add (index, this);
 			} else {
 				GTK.gtk_tree_store_insert (parent.modelHandle, handle, parentIter, index);
 				siblings.add (index, this);
@@ -859,7 +863,9 @@ public TreeItem getItem (int index) {
 	if (index < 0) error (SWT.ERROR_INVALID_RANGE);
 	if (index >= items.size()) error (SWT.ERROR_INVALID_RANGE);
 	if (!parent.checkData (this)) error (SWT.ERROR_WIDGET_DISPOSED);
-	return parent._getItem(this, items, index);
+	TreeItem result = parent._getItem(this, items, index);
+	assert result.treeStoreIndexOf() == index;
+	return result;
 }
 
 TreeItem _peekItem (int index) {