[Python-Dev] results of id() and weakref.getweakrefs() sometimes break on object resurrection

[Stefan Richthofer]

Okay, sorry, I was thinking too Jython-like. I fixed runGC() just to
see now that it does not even trigger resurrection, since under
CPython there are no finalizers executed in ref cycles (i.e. I find my
objects in gc.garbage).
So I realize, my xy_cyclic tests are pointless anyway since in cyclic
gc no resurrection can happen.

> The second problem (with weakref) is different: weakrefs are cleared
> before __del__ is called, so resurrection doesn't affect the whole
> process.
It appears weakrefs are only cleared if this is done by gc (where no
resurrection can happen anyway). If a resurrection-performing-__del__ is
just called by ref-count-drop-to-0, weakrefs persist - a behavior that is
very difficult and inefficient to emulate in Jython, but I'll give it
some more thoughts...

However thanks for the help!

-Stefan


> Gesendet: Sonntag, 26. Oktober 2014 um 01:22 Uhr
> Von: "Antoine Pitrou" <solipsis at pitrou.net>
> An: python-dev at python.org
> Betreff: Re: [Python-Dev] results of id() and weakref.getweakrefs() sometimes break on object resurrection
>
> 
> Hello Stefan,
> 
> On Sun, 26 Oct 2014 00:20:47 +0200
> "Stefan Richthofer" <Stefan.Richthofer at gmx.de> wrote:
> > Hello developers,
> > 
> > I observed strange behaviour in CPython (tested in 2.7.5 and 3.3.3)
> > regarding object resurrection.
> 
> Your runGC() function is buggy, it does not run the GC under CPython.
> Fix it and the first problem (with id()) disappears.
> 
> The second problem (with weakref) is different: weakrefs are cleared
> before __del__ is called, so resurrection doesn't affect the whole
> process. Add a callback to the weakref and you'll see it is getting
> called.
> 
> In other words, CPython behaves as expected. Your concern is
> appreciated, though.
> 
> Regards
> 
> Antoine.
> 
> 
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