Signalmanager

Description

The class Signalmanager in p/sources/pyside6/libpyside takes care of routing Qt signals to the receivers (files signalmanager.cpp, qobjectconnect.cpp, pysidesignal.cpp).

There are several kinds of receivers:

• Slots of C++ classes

• Slots of QObject-derived classes declared in Python using @Slot

• Functions of QObject-derived classes declared in Python. They will be turned into proper slots at runtime using the private Qt class QMetaObjectBuilder. This causes a warning to be emitted, visible when activating the logging category qt.pyside.libpyside.

• Methods of non-QObject-derived classes

• Other callables (free functions, lambdas, partially bound functions)

Proper Qt connections where QObject.disconnect(), QObject.sender() and QObject.connectNotify() work are desirable also for receivers that are not QObjects. This is achieved by using a QObject-derived class GlobalReceiverV2 for a receiver which has a dynamic slot created by QMetaObjectBuilder to route connected signals to the Python receiver (based on internal class DynamicSlotDataV2).

The instances of GlobalReceiverV2 are stored in a hash on the receiver Python objects in Signalmanager.

QMetaObject::connect(QObject*,int,QObject*,int) is used to make the connections based on meta method indexes.

Normally, a reference should be kept on the receiver callable. However, in the case of a method of a non-QObject-derived class, the connection should be automatically severed when the instance is deleted. The callable passed in this case (signal.connect(foo.slot)) is a partially bound function which has the self parameter. It is decomposed into the self parameter and the method. A reference is kept on the method. A weak reference with destruction callback is kept for self.

Issues

• Receiver Leak PYSIDE-1057

• Partial function receiver Leak PYSIDE-2793

• Various issues related to threading and object deletion, solved by workarounds (PYSIDE-2646)

• Complicated code, hard to maintain

• Disconnect does not work for QObject.connect() with context argument; it also leaks methods

Plans

Change QObject: Add connect() overload with context arg acab25a3ccb836818e5089b23d40196bc7414b7a implements a connection based on QtPrivate::QSlotObjectBase and QObjectPrivate::connect(QObject*,int,QObject*,QtPrivate::QSlotObjectBase*) (pysideqslotobject.cpp). This could in principle enable removing GlobalReceiverV2, but requires keeping the QMetaObject::Connection for disconnecting.