Shave ~5% off from signal emission time

Refactor activate(), so that we eliminate almost all
checks for signal hooks in the common case.

Here are the benchmark numbers showing the improvement
for 100M signal emissions

                       without change    with change
string based connect:  3836              3693
pointer based connect: 4571              4510
not connected:          479               433
disconnected:           559               522

Change-Id: I394e6ea5d5bc96e298e8cc0c763eed78c8041876
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/corelib/kernel/qobject_p.h b/src/corelib/kernel/qobject_p.h
index 7cc82d4f71..a260ed680e 100644
--- a/src/corelib/kernel/qobject_p.h
+++ b/src/corelib/kernel/qobject_p.h
@@ -79,9 +79,9 @@ struct QSignalSpyCallbackSet
     EndCallback signal_end_callback,
                 slot_end_callback;
 };
-void Q_CORE_EXPORT qt_register_signal_spy_callbacks(const QSignalSpyCallbackSet &callback_set);
+void Q_CORE_EXPORT qt_register_signal_spy_callbacks(QSignalSpyCallbackSet *callback_set);
 
-extern QSignalSpyCallbackSet Q_CORE_EXPORT qt_signal_spy_callback_set;
+extern Q_CORE_EXPORT QBasicAtomicPointer<QSignalSpyCallbackSet> qt_signal_spy_callback_set;
 
 enum { QObjectPrivateVersion = QT_VERSION };