Fix detecting infinite loops in PolishLoopDetector

Resetting counter too early was causing infinite loop in a function
responsible for detecting infinite loops (how ironic). Fix this
behavior.
Decrease the threshold for detecting infinite loop from 100k to 10k
iterations for better responsiveness.

Fixes: QTBUG-126474
Pick-to: 6.5 6.7 6.8
Change-Id: Ife45e694d417b1d23fa1294e069ee54eff31c047
Reviewed-by: Jan Arve Sæther <[email protected]>

2 files changed, 25 insertions, 31 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index bb11eb4d98..a39efbb23a 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -287,37 +287,31 @@ struct PolishLoopDetector
         if (itemsToPolish.size() > itemsRemainingBeforeUpdatePolish) {
             // Detected potential polish loop.
             ++numPolishLoopsInSequence;
-            if (numPolishLoopsInSequence >= 1000) {
+            if (numPolishLoopsInSequence == 10000) {
+                // We have looped 10,000 times without actually reducing the list of items to
+                // polish, give up for now.
+                // This is not a fix, just a remedy so that the application can be somewhat
+                // responsive.
+                numPolishLoopsInSequence = 0;
+                return true;
+            }
+            if (numPolishLoopsInSequence >= 1000 && numPolishLoopsInSequence < 1005) {
                 // Start to warn about polish loop after 1000 consecutive polish loops
-                if (numPolishLoopsInSequence == 100000) {
-                    // We have looped 100,000 times without actually reducing the list of items to
-                    // polish, give up for now.
-                    // This is not a fix, just a remedy so that the application can be somewhat
-                    // responsive.
-                    numPolishLoopsInSequence = 0;
-                    return true;
-                } else if (numPolishLoopsInSequence < 1005) {
-                    // Show the 5 next items involved in the polish loop.
-                    // (most likely they will be the same 5 items...)
-                    QQuickItem *guiltyItem = itemsToPolish.last();
-                    qmlWarning(item) << "possible QQuickItem::polish() loop";
-
-                    auto typeAndObjectName = [](QQuickItem *item) {
-                        QString typeName = QQmlMetaType::prettyTypeName(item);
-                        QString objName = item->objectName();
-                        if (!objName.isNull())
-                            return QLatin1String("%1(%2)").arg(typeName, objName);
-                        return typeName;
-                    };
-
-                    qmlWarning(guiltyItem) << typeAndObjectName(guiltyItem)
-                               << " called polish() inside updatePolish() of " << typeAndObjectName(item);
-
-                    if (numPolishLoopsInSequence == 1004)
-                        // Enough warnings. Reset counter in order to speed things up and re-detect
-                        // more loops
-                        numPolishLoopsInSequence = 0;
-                }
+                // Show the 5 next items involved in the polish loop.
+                // (most likely they will be the same 5 items...)
+                QQuickItem *guiltyItem = itemsToPolish.last();
+                qmlWarning(item) << "possible QQuickItem::polish() loop";
+
+                auto typeAndObjectName = [](QQuickItem *item) {
+                    QString typeName = QQmlMetaType::prettyTypeName(item);
+                    QString objName = item->objectName();
+                    if (!objName.isNull())
+                        return QLatin1String("%1(%2)").arg(typeName, objName);
+                    return typeName;
+                };
+
+                qmlWarning(guiltyItem) << typeAndObjectName(guiltyItem)
+                            << " called polish() inside updatePolish() of " << typeAndObjectName(item);
             }
         } else {
             numPolishLoopsInSequence = 0;
diff --git a/tests/auto/quick/qquickitem/tst_qquickitem.cpp b/tests/auto/quick/qquickitem/tst_qquickitem.cpp
index 338070b730..2c89744e9e 100644
--- a/tests/auto/quick/qquickitem/tst_qquickitem.cpp
+++ b/tests/auto/quick/qquickitem/tst_qquickitem.cpp
@@ -1529,7 +1529,7 @@ void tst_qquickitem::polishLoopDetection_data()
 
     QTest::newRow("test1.100") <<   PolishItemSpans({ {1, 100} }) << 0;
     QTest::newRow("test1.1002") <<  PolishItemSpans({ {1, 1002} }) << 3;
-    QTest::newRow("test1.2020") <<  PolishItemSpans({ {1, 2020} }) << 10;
+    QTest::newRow("test1.2020") <<  PolishItemSpans({ {1, 2020} }) << 5;
 
     QTest::newRow("test5.1") <<    PolishItemSpans({ {5, 1} }) << 0;
     QTest::newRow("test5.10") <<   PolishItemSpans({ {5, 10} }) << 0;