libcamera: signal: Disconnect signal automatically on slot deletion

When a signal is connected to a member function slot, the slot is not
disconnected when the slot object is deleted. This can lead to calling a
member function of a deleted object if the signal isn't disconnected
manually by the slot object's destructor.

Make signal handling easier by implementing a base Object class that
tracks all connected signals and disconnects from them automatically
when the object is deleted, using template specialization resolution in
the Signal class.

As inheriting from the Object class may to a too harsh requirement for
Signal usage in applications, keep the existing behaviour working if the
slot doesn't inherit from the Object class. We may reconsider this later
and require all slot objects to inherit from the Object class.

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

1 files changed, 37 insertions, 0 deletions

diff --git a/test/signal.cpp b/test/signal.cpp
index ab69ca1b..19a52c60 100644
--- a/test/signal.cpp
+++ b/test/signal.cpp
@@ -8,6 +8,7 @@
 #include <iostream>
 #include <string.h>
 
+#include <libcamera/object.h>
 #include <libcamera/signal.h>
 
 #include "test.h"
@@ -22,6 +23,15 @@ static void slotStatic(int value)
 	valueStatic_ = value;
 }
 
+class SlotObject : public Object
+{
+public:
+	void slot()
+	{
+		valueStatic_ = 1;
+	}
+};
+
 class SignalTest : public Test
 {
 protected:
@@ -139,6 +149,33 @@ protected:
 			return TestFail;
 		}
 
+		/*
+		 * Test automatic disconnection on object deletion. Connect the
+		 * slot twice to ensure all instances are disconnected.
+		 */
+		signalVoid_.disconnect();
+
+		SlotObject *slotObject = new SlotObject();
+		signalVoid_.connect(slotObject, &SlotObject::slot);
+		signalVoid_.connect(slotObject, &SlotObject::slot);
+		delete slotObject;
+		valueStatic_ = 0;
+		signalVoid_.emit();
+		if (valueStatic_ != 0) {
+			cout << "Signal disconnection on object deletion test failed" << endl;
+			return TestFail;
+		}
+
+		/*
+		 * Test that signal deletion disconnects objects. This shall
+		 * not generate any valgrind warning.
+		 */
+		Signal<> *signal = new Signal<>();
+		slotObject = new SlotObject();
+		signal->connect(slotObject, &SlotObject::slot);
+		delete signal;
+		delete slotObject;
+
 		return TestPass;
 	}