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, 4 insertions, 0 deletions

diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index bcbc45cdbe..c0bb812904 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -831,9 +831,11 @@ QObject::~QObject()
             if (senderLists)
                 senderLists->dirty = true;
 
+            int signal_index = node->signal_index;
             node = node->next;
             if (needToUnlock)
                 m->unlock();
+            sender->disconnectNotify(QMetaObjectPrivate::signal(sender->metaObject(), signal_index));
         }
     }
 
@@ -3021,6 +3023,7 @@ QObjectPrivate::Connection *QMetaObjectPrivate::connect(const QObject *sender,
 
     QScopedPointer<QObjectPrivate::Connection> c(new QObjectPrivate::Connection);
     c->sender = s;
+    c->signal_index = signal_index;
     c->receiver = r;
     c->method_relative = method_index;
     c->method_offset = method_offset;
@@ -4188,6 +4191,7 @@ QMetaObject::Connection QObject::connectImpl(const QObject *sender, void **signa
 
     QScopedPointer<QObjectPrivate::Connection> c(new QObjectPrivate::Connection);
     c->sender = s;
+    c->signal_index = signal_index;
     c->receiver = r;
     c->slotObj = slotObj;
     c->connectionType = type;