Simplify object lifetime management when moving objects to a QThread

The documentation for Qt::AutoConnection states is a signal is emitted
from the same thread as the receiving object, the connection should
behave as Qt::DirectConnection. The actual behavior prior to this commit
was different from the documentation; if the signal was emitted in a
thread different from the sender's thread, then we would queue (which is
now corrected). By making the behavior match the documentation, it is
now possible to connect QThread's finished() signal to an object's
deleteLater() slot and the slot will execute when finished() is emitted
(previously it was queued).

QObject::deleteLater() uses a posted QEvent::DeferredDelete event to
trigger deletion of the object. In QThread, after emitting the
finished() signal, we now send all pending DeferredDelete events to
ensure that all pending deletions happen. We have precedence for this
behavior, QCoreApplication::exec() does the same thing after emitting
the aboutToQuit() signal.

Reviewed-by: joao
Reviewed-by: olivier

2 files changed, 92 insertions, 0 deletions

diff --git a/tests/auto/qobject/tst_qobject.cpp b/tests/auto/qobject/tst_qobject.cpp
index 24cd5a3..a09f109 100644
--- a/tests/auto/qobject/tst_qobject.cpp
+++ b/tests/auto/qobject/tst_qobject.cpp
@@ -134,6 +134,7 @@ private slots:
     void connectConstructorByMetaMethod();
     void disconnectByMetaMethod();
     void disconnectNotSignalMetaMethod();
+    void autoConnectionBehavior();
 
 protected:
 };
@@ -3847,5 +3848,82 @@ void tst_QObject::disconnectNotSignalMetaMethod()
     QVERIFY(!QObject::disconnect(&s, slot, &r, QMetaMethod()));
 }
 
+class ThreadAffinityThread : public QThread
+{
+public:
+    SenderObject *sender;
+
+    ThreadAffinityThread(SenderObject *sender)
+        : sender(sender)
+    { }
+    void run()
+    {
+        sender->emitSignal1();
+    }
+};
+
+void tst_QObject::autoConnectionBehavior()
+{
+    SenderObject *sender = new SenderObject;
+    ReceiverObject *receiver = new ReceiverObject;
+    connect(sender, SIGNAL(signal1()), receiver, SLOT(slot1()));
+
+    // at emit, currentThread == sender->thread(), currentThread == receiver->thread(), sender->thread() == receiver->thread()
+    QVERIFY(!receiver->called(1));
+    sender->emitSignal1();
+    QVERIFY(receiver->called(1));
+    receiver->reset();
+
+    // at emit, currentThread != sender->thread(), currentThread != receiver->thread(), sender->thread() == receiver->thread()
+    ThreadAffinityThread emitThread1(sender);
+    QVERIFY(!receiver->called(1));
+    emitThread1.start();
+    QVERIFY(emitThread1.wait(30000));
+    QVERIFY(!receiver->called(1));
+    QCoreApplication::sendPostedEvents(receiver, QEvent::MetaCall);
+    QVERIFY(receiver->called(1));
+    receiver->reset();
+
+    // at emit, currentThread == sender->thread(), currentThread != receiver->thread(), sender->thread() != receiver->thread()
+    sender->moveToThread(&emitThread1);
+    QVERIFY(!receiver->called(1));
+    emitThread1.start();
+    QVERIFY(emitThread1.wait(30000));
+    QVERIFY(!receiver->called(1));
+    QCoreApplication::sendPostedEvents(receiver, QEvent::MetaCall);
+    QVERIFY(receiver->called(1));
+    receiver->reset();
+
+    // at emit, currentThread != sender->thread(), currentThread == receiver->thread(), sender->thread() != receiver->thread()
+    QVERIFY(!receiver->called(1));
+    sender->emitSignal1();
+    QVERIFY(receiver->called(1));
+    receiver->reset();
+
+    // at emit, currentThread != sender->thread(), currentThread != receiver->thread(), sender->thread() != receiver->thread()
+    ThreadAffinityThread emitThread2(sender);
+    QThread receiverThread;
+    QTimer *timer = new QTimer;
+    timer->setSingleShot(true);
+    timer->setInterval(100);
+    connect(&receiverThread, SIGNAL(started()), timer, SLOT(start()));
+    connect(timer, SIGNAL(timeout()), &receiverThread, SLOT(quit()), Qt::DirectConnection);
+    connect(&receiverThread, SIGNAL(finished()), timer, SLOT(deleteLater()));
+    timer->moveToThread(&receiverThread);
+
+    receiver->moveToThread(&receiverThread);
+    QVERIFY(!receiver->called(1));
+    emitThread2.start();
+    QVERIFY(emitThread2.wait(30000));
+    QVERIFY(!receiver->called(1));
+    receiverThread.start();
+    QVERIFY(receiverThread.wait(30000));
+    QVERIFY(receiver->called(1));
+    receiver->reset();
+
+    delete sender;
+    delete receiver;
+}
+
 QTEST_MAIN(tst_QObject)
 #include "tst_qobject.moc"
diff --git a/tests/auto/qthread/tst_qthread.cpp b/tests/auto/qthread/tst_qthread.cpp
index 843749a..f290a2b 100644
--- a/tests/auto/qthread/tst_qthread.cpp
+++ b/tests/auto/qthread/tst_qthread.cpp
@@ -106,6 +106,7 @@ private slots:
     void adoptMultipleThreads();
 
     void QTBUG13810_exitAndStart();
+    void connectThreadFinishedSignalToObjectDeleteLaterSlot();
 
     void stressTest();
 };
@@ -975,6 +976,19 @@ void tst_QThread::QTBUG13810_exitAndStart()
     QCOMPARE(sync1.m_prop, 89);
 }
 
+void tst_QThread::connectThreadFinishedSignalToObjectDeleteLaterSlot()
+{
+    QThread thread;
+    QObject *object = new QObject;
+    QWeakPointer<QObject> p = object;
+    QVERIFY(!p.isNull());
+    connect(&thread, SIGNAL(started()), &thread, SLOT(quit()), Qt::DirectConnection);
+    connect(&thread, SIGNAL(finished()), object, SLOT(deleteLater()));
+    object->moveToThread(&thread);
+    thread.start();
+    QVERIFY(thread.wait(30000));
+    QVERIFY(p.isNull());
+}
 
 QTEST_MAIN(tst_QThread)
 #include "tst_qthread.moc"