[PyQt] How SIP detects that a QObject need to destruct.

[Erik Janssens]

creating/deleting children does not change the refcount
of a QObject, since this is done purely in C++

On Thu, 2012-03-29 at 19:22 +0800, Goldfish Huang wrote:
> Hi, all.
> 
> I am doubted how  SIP deal with QObject's cycle reference, when I try
> to fix some unknown memory leaks. It seems that SIP only keep a
> reference to QObject, whatever how many children it has. Then a
> QObject must have not less than 2 reference count, one from Python and
> another from SIP. The question is, when I delete the QObject from
> Python, how SIP detects that and decrease the reference? It supposed
> that the reference count will be decreased to 1, and never destructed.
> 
> The code pastes below:
> 
>     import sys, gc
>     from PyQt4.QtCore import *
> 
>     gc.disable()
>     c=QObjectCleanupHandler()
>     o1=QObject()
>     QObject(o1), QObject(o1)
>     c.add(o1)
>     print sys.getrefcount(o1) , len(o1.children())
> 
>     #delete a child but the reference count remains 2.
>     o1.children()[0].setParent(None)
>     print sys.getrefcount(o1) , len(o1.children())
> 
>     #decrease reference count of o1 by one.
>     del o1
> 
>     #It is destructed!
>     print c.isEmpty()
> 
> 
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