[PyKDE] Double free() problem in PyQt 3.15.1??

Phil Thompson phil at riverbankcomputing.co.uk
Sat Mar 11 19:26:12 GMT 2006

On Saturday 11 March 2006 7:13 pm, Simon Edwards wrote:
> Hi Phil and everybody else,
> I'm busy working on polishing and debugging stuff for the coming Kubuntu
> release, which makes increasingly more use of PyQt+PyKDE BTW.
> Anyway, I think I've come across a double free memory bug in PyQt 3.15.1.
> Qt complains about a "Double QObject deletion detected.", and valgrind
> points to a problem in sipKDialogBase::~sipKDialogBase(). (Reading memory
> which is already free'd, and invalid free(), delete etc). This problem only
> appears when my app opens a dialog.

Opens it? Or when the name goes out of scope?

> This problem does not occur with PyQt 3.14.1. Comparing the two PyQt
> releases I see this added to the 3.15.1 qdialog.sip:
> -----------------------------
> %If (- Qt_3_0_0)
> 	int exec() /PyName=exec_loop, ReleaseGIL,
> 		    PreHook=__pyQtPreEventLoopHook__,
> 		    PostHook=__pyQtPostEventLoopHook__/;
> %MethodCode
> 		// Transfer ownership back to Python (a modal dialog will
> 		// probably have the main window as it's parent).  This means
> 		// the Qt dialog will be deleted when the Python wrapper is
> 		// garbage collected.  Although this is a little inconsistent,
> 		// it saves having to code it explicitly to avoid the memory
> 		// leak.
> 		sipTransferBack(sipSelf);
> 		sipRes = sipCpp->QDialog::exec();
> %End
> %End
> -----------------------------
> This does look like it could be the problem. Phil?

Possibly. How are you constructing the dialog? Does it have a parent? Are the 
references to it local or global?


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