QTimer: fix new-style slot invocation for receiver in another thread

For single-shot timers, at least. QSingleShotTimer had either an
optimization or the only way to make new-style slot invocations by
storing the QSlotObject pointer and calling it directly. Instead of
doing that, let's just actually connect and let QObject handle the
actual delivery.

[ChangeLog][QtCore][QTimer] Fixed a bug that caused slots connected to
single-slot timers using the new-style connection mechanism to be
delivered in the wrong thread.

Fixes: QTBUG-112162
Pick-to: 5.15 6.2 6.5
Change-Id: Idd5e1bb52be047d7b4fffffd174eadb227ab65ee
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/tests/auto/corelib/kernel/qtimer/tst_qtimer.cpp b/tests/auto/corelib/kernel/qtimer/tst_qtimer.cpp
index e2bde37a7e..5c39fc5d91 100644
--- a/tests/auto/corelib/kernel/qtimer/tst_qtimer.cpp
+++ b/tests/auto/corelib/kernel/qtimer/tst_qtimer.cpp
@@ -1006,18 +1006,21 @@ void tst_QTimer::postedEventsShouldNotStarveTimers()
 }
 
 struct DummyFunctor {
-    void operator()() {}
+    static QThread *callThread;
+    void operator()() { callThread = QThread::currentThread(); }
 };
+QThread *DummyFunctor::callThread = nullptr;
 
 void tst_QTimer::crossThreadSingleShotToFunctor()
 {
-    // We're testing for crashes here, so the test simply running to
-    // completion is considered a success
+    // We're also testing for crashes here, so the test simply running to
+    // completion is part of the success
     QThread t;
     t.start();
 
     QObject* o = new QObject();
     o->moveToThread(&t);
+    DummyFunctor::callThread = nullptr;
 
     for (int i = 0; i < 10000; i++) {
         QTimer::singleShot(0, o, DummyFunctor());
@@ -1026,6 +1029,8 @@ void tst_QTimer::crossThreadSingleShotToFunctor()
     t.quit();
     t.wait();
     delete o;
+
+    QCOMPARE(DummyFunctor::callThread, &t);
 }
 
 void tst_QTimer::callOnTimeout()