CanvasTextureImageFactory: fix quadratic loop in notifyLoadedImages()

The old code uses a Java-style iterator on a QList, but
failed to use the iterator's remove() function, opting
instead to call QList::removeOne(). Both would have been
quadratic, but the current code is even worse in that it
re-scans the list for the element 'it' currently points
at.

Fix by using std::remove_if, which is linear, and, since
it doesn't take a copy of the container, also avoids a
deep copy of 'm_loadingImagesList' on actual removal (it
will attempt to detach unconditional now, due to the use
of non-const begin()/end(), but the variable is now no
longer shared with anyone, so there will actually be no
detach.

Change-Id: I71cd08bd40994e86a6470fdd9bcd55c18913b8d8
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 9 insertions, 6 deletions

diff --git a/src/imports/qtcanvas3d/teximage3d.cpp b/src/imports/qtcanvas3d/teximage3d.cpp
index 315b395..402313e 100644
--- a/src/imports/qtcanvas3d/teximage3d.cpp
+++ b/src/imports/qtcanvas3d/teximage3d.cpp
@@ -116,17 +116,20 @@ void CanvasTextureImageFactory::notifyLoadedImages()
     if (!m_loadingImagesList.size())
         return;
 
-    QMutableListIterator<CanvasTextureImage *> it(m_loadingImagesList);
-    while (it.hasNext()) {
-        CanvasTextureImage *image = it.next();
+    auto hasLoadingFinishedOrFailed = [](CanvasTextureImage *image) -> bool {
         if (image->imageState() == CanvasTextureImage::LOADING_FINISHED) {
-            m_loadingImagesList.removeOne(image);
             image->emitImageLoaded();
+            return true;
         } else if (image->imageState() == CanvasTextureImage::LOADING_ERROR) {
-            m_loadingImagesList.removeOne(image);
             image->emitImageLoadingError();
+            return true;
         }
-    }
+        return false;
+    };
+
+    m_loadingImagesList.erase(std::remove_if(m_loadingImagesList.begin(), m_loadingImagesList.end(),
+                                             hasLoadingFinishedOrFailed),
+                              m_loadingImagesList.end());
 }
 
 /*!