libcamera: signal: Make slots list private

The slots list is touched from most of the Signal template functions. In
order to prepare for thread-safety, move handling of the list to a small
number of non-template functions in the SignalBase class.

This incidently fixes a bug in signal disconnection handling where the
signal wasn't removed from the object's signals list, as pointed out by
the signals unit test.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/object.cpp

@@ -76,7 +76,12 @@ Object::Object(Object *parent)
  */
 Object::~Object()
 {
-	for (SignalBase *signal : signals_)
+	/*
+	 * Move signals to a private list to avoid concurrent iteration and
+	 * deletion of items from Signal::disconnect().
+	 */
+	std::list<SignalBase *> signals(std::move(signals_));
+	for (SignalBase *signal : signals)
 		signal->disconnect(this);
 
 	if (pendingMessages_)

src/libcamera/signal.cpp

@@ -14,6 +14,42 @@
 
 namespace libcamera {
 
+void SignalBase::connect(BoundMethodBase *slot)
+{
+	Object *object = slot->object();
+	if (object)
+		object->connect(this);
+	slots_.push_back(slot);
+}
+
+void SignalBase::disconnect(Object *object)
+{
+	disconnect([object](SlotList::iterator &iter) {
+		return (*iter)->match(object);
+	});
+}
+
+void SignalBase::disconnect(std::function<bool(SlotList::iterator &)> match)
+{
+	for (auto iter = slots_.begin(); iter != slots_.end(); ) {
+		if (match(iter)) {
+			Object *object = (*iter)->object();
+			if (object)
+				object->disconnect(this);
+
+			delete *iter;
+			iter = slots_.erase(iter);
+		} else {
+			++iter;
+		}
+	}
+}
+
+SignalBase::SlotList SignalBase::slots()
+{
+	return slots_;
+}
+
 /**
  * \class Signal
  * \brief Generic signal and slot communication mechanism