Call QObject::disconnectNotify() when receiver is destroyed

Store the signal index in QObjectPrivate::Connection, thereby making
it available in "implicit" disconnect contexts (i.e., receiver
deletion).

This change does not cause the size of QObjectPrivate::Connection
to grow (still 40 bytes on 32-bit Linux, 72 bytes on 64-bit Mac).

Valgrinding the new benchmark indicates that the percentage of the
time spent in the QObject destructor increased from 7.8% to 8.4%
on ia32, for that particular stress test; the increase is the
combined cost of calling metaObject(), QMetaObjectPrivate::signal(),
and disconnectNotify() for one connection. In practice, the measured
wallclock time increased by about 3ms for a 500ms run (which
repeatedly constructs, connects, and destroys an object).

Task-number: QTBUG-4844

Change-Id: I1beb01c753f31542fc0acb62edb4c6d165fcc5b4
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

1 files changed, 20 insertions, 2 deletions

diff --git a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
index 0cdce500fa..479cdd3ca8 100644
--- a/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
+++ b/tests/auto/corelib/kernel/qobject/tst_qobject.cpp
@@ -978,8 +978,26 @@ void tst_QObject::disconnectNotify_receiverDestroyed()
     QVERIFY(QObject::connect((SenderObject*)s, SIGNAL(signal1()), (ReceiverObject*)r, SLOT(slot1())));
 
     delete r;
-    // disconnectNotify() is not called, but it probably should be.
-    QVERIFY(s->disconnectedSignals.isEmpty());
+    QCOMPARE(s->disconnectedSignals.count(), 1);
+    QCOMPARE(s->disconnectedSignals.at(0), QMetaMethod::fromSignal(&SenderObject::signal1));
+
+    s->disconnectedSignals.clear();
+    r = new NotifyObject;
+
+    QVERIFY(QObject::connect((SenderObject*)s, SIGNAL(signal3()), (ReceiverObject*)r, SLOT(slot3())));
+
+    delete r;
+    QCOMPARE(s->disconnectedSignals.count(), 1);
+    QCOMPARE(s->disconnectedSignals.at(0), QMetaMethod::fromSignal(&SenderObject::signal3));
+
+    s->disconnectedSignals.clear();
+    r = new NotifyObject;
+
+    QVERIFY(QObject::connect((SenderObject*)s, SIGNAL(destroyed()), (ReceiverObject*)r, SLOT(slot3())));
+
+    delete r;
+    QCOMPARE(s->disconnectedSignals.count(), 1);
+    QCOMPARE(s->disconnectedSignals.at(0), QMetaMethod::fromSignal(&QObject::destroyed));
 
     delete s;
 }