Windows: fix DeferredDelete events processing on QThread::terminate()

On finishing/terminating a thread, when processing posted events,
we need to consider QThread's own data instead of caller thread's data.
Otherwise we can get into unexpected situations such as double
destruction of an object, premature destruction, etc.

Fixes: QTBUG-103922
Pick-to: 6.4 6.3 6.3.1 6.2 5.15
Change-Id: Idf77221ebbaa0b150ee2d0c296b51829ae8dc30e
Reviewed-by: Thiago Macieira <[email protected]>

src/corelib/thread/qthread_win.cpp

@@ -293,6 +293,17 @@ unsigned int __stdcall QT_ENSURE_STACK_ALIGNED_FOR_SSE QThreadPrivate::start(voi
     return 0;
 }
 
+/*
+    For regularly terminating threads, this will be called and executed by the thread as the
+    last code before the thread exits. In that case, \a arg is the current QThread.
+
+    However, this function will also be called by QThread::terminate (as well as wait() and
+    setTerminationEnabled) to give Qt a chance to update the terminated thread's state and
+    process pending DeleteLater events for objects that live in the terminated thread. And for
+    adopted thread, this method is called by the thread watcher.
+
+    In those cases, \a arg will not be the current thread.
+*/
 void QThreadPrivate::finish(void *arg, bool lockAnyway) noexcept
 {
     QThread *thr = reinterpret_cast<QThread *>(arg);
@@ -305,7 +316,7 @@ void QThreadPrivate::finish(void *arg, bool lockAnyway) noexcept
     if (lockAnyway)
         locker.unlock();
     emit thr->finished(QThread::QPrivateSignal());
-    QCoreApplication::sendPostedEvents(0, QEvent::DeferredDelete);
+    QCoreApplicationPrivate::sendPostedEvents(nullptr, QEvent::DeferredDelete, d->data);
     QThreadStorageData::finish(tls_data);
     if (lockAnyway)
         locker.relock();

tests/auto/corelib/thread/qthread/tst_qthread.cpp

@@ -91,6 +91,9 @@ private slots:
     void create();
     void createDestruction();
     void threadIdReuse();
+
+    void terminateAndPrematureDestruction();
+    void terminateAndDoubleDestruction();
 };
 
 enum { one_minute = 60 * 1000, five_minutes = 5 * one_minute };
@@ -1719,5 +1722,80 @@ void tst_QThread::threadIdReuse()
     }
 }
 
+class WaitToRun_Thread : public QThread
+{
+    Q_OBJECT
+public:
+    void run() override
+    {
+        emit running();
+        QThread::exec();
+    }
+
+Q_SIGNALS:
+    void running();
+};
+
+
+void tst_QThread::terminateAndPrematureDestruction()
+{
+    WaitToRun_Thread thread;
+    QSignalSpy spy(&thread, &WaitToRun_Thread::running);
+    thread.start();
+    QVERIFY(spy.wait(500));
+
+    QScopedPointer<QObject> obj(new QObject);
+    QPointer<QObject> pObj(obj.data());
+    obj->deleteLater();
+
+    thread.terminate();
+    QVERIFY2(pObj, "object was deleted prematurely!");
+    thread.wait(500);
+}
+
+void tst_QThread::terminateAndDoubleDestruction()
+{
+    class ChildObject : public QObject
+    {
+    public:
+        ChildObject(QObject *parent)
+            : QObject(parent)
+        {
+            QSignalSpy spy(&thread, &WaitToRun_Thread::running);
+            thread.start();
+            spy.wait(500);
+        }
+
+        ~ChildObject()
+        {
+            QVERIFY2(!inDestruction, "Double object destruction!");
+            inDestruction = true;
+            thread.terminate();
+            thread.wait(500);
+        }
+
+        bool inDestruction = false;
+        WaitToRun_Thread thread;
+    };
+
+    class TestObject : public QObject
+    {
+    public:
+        TestObject()
+            : child(new ChildObject(this))
+        {
+        }
+
+        ~TestObject()
+        {
+            child->deleteLater();
+        }
+
+        ChildObject *child = nullptr;
+    };
+
+    TestObject obj;
+}
+
 QTEST_MAIN(tst_QThread)
 #include "tst_qthread.moc"