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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-07-11 13:02:30 +0300
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-07-11 16:38:24 +0300
commit56c2e653008a5447eafc7509e6e2957470853495 (patch)
treeec0c664c79d0b41dc7fe7bb68506067ae5bd5a15 /README.md
parentb462f2bfd6c5672a7e2f108bd2fcd4b419f1b25b (diff)
libcamera: signal: Fix Object handling in multiple inheritance cases
The SlotBase implementation stores the receiver object pointer as a void pointer internally. The pointer is then cast back to an Object pointer when the receiver object class derives from Object. When the receiver is an object that inherits from both the Object class and other classes, the Object data members may not be stored at the beginning of the object memory. The cast back to an Object pointer is thus incorrect. Fix this by casting the receiver object pointer to an Object pointer where the type of the receiver object is known, and pass it along with the receiver void pointer to the SlotBase class. The SlotBase class stores both pointers internally, and doesn't need the isObject_ field anymore as the same information is obtained from checking if the Object pointer is null. To avoid confusing the two pointers, use the same naming scheme through the whole implementation: "obj" points to a receiver object as an unknown type, and "object" to the receiver object cast to an Object. The latter is null when the receiver object doesn't inherit from the Object class. To further clarify the code, remove direct access to the SlotBase "obj" and "object" fields as much as possible. They are replaced by two new methods : - SlotBase::disconnect() to disconnect a signal from the slot's receiver object - SlotBase::match() to test if an object pointer matches the slot The match() method is a template method with a specialisation for the Object type, to compare either the obj or the object pointer depending on the type of the parameter. This is required as the Object destructor calls the SignalBase::disconnect() method for signal connected to the object, and passes a pointer to Object to that method, while the actual object may have a different address due to the issue explained above. The pointer must thus be compared with the stored Object pointer in that case, not to the pointer to the receiver object. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
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