How to check what is holding reference to object
in [Python]
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From: Chris Rebert on 27 Apr 2010 18:02 On Tue, Apr 27, 2010 at 2:58 PM, Chris Rebert <clp2(a)rebertia.com> wrote: > On Tue, Apr 27, 2010 at 2:42 PM, Michal M <mich.mierzwa(a)googlemail.com> wrote: >> On 27 Kwi, 23:21, Duncan Booth <duncan.bo...(a)invalid.invalid> wrote: >>> Michal M <mich.mier...(a)googlemail.com> wrote: >>> > I've just found out that one of objects is not destroyed when it >>> > should be. This means that something was holding reference to this >>> > object or part of it (i.e. method). Is there any way to check what >>> > holds that reference? I am unable to do that just looking to the code >>> > or debugging it because it is pretty complicated, but I am able to >>> > invoke this situation again. >>> >>> See if this code helps: >>> >>> http://groups.google.com/group/comp.lang.python/browse_thread/thread/.... >>> >>> It's pretty old so it may need some adjustment, but I wrote it >>> to figure out exactly that sort of problem. >> >> Thanks you for answers. >> I tried to use gc.get_referrers(self) in point in code when according >> to me object should be destroyed earlier but I did not see anything >> interesting. Then just realised that gc will not destroy object even >> when itself holds reference to his own method. >> >> For example >> >> class A(object): >> Â def a(self): >> Â Â pass >> Â def b(self): >> Â Â self.method = self.a >> Â def __del__(self): >> Â Â print "A object deleted" >> >>>> a = A() >>>> del a >> A object delted >>>> a = A() >>>> a.b() >>>> del a >> ... nothing ... >> >> I thought gc would discover such circle loops but apparently it did >> not. > > No, it does, you just didn't give it long enough; for performance > reasons, cyclical GC is only done every so often: Addendum: Also, defining __del__ in your example was likely problematic: See http://docs.python.org/library/gc.html#gc.garbage - Chris
From: Michal M on 28 Apr 2010 03:01 On Apr 28, 12:02 am, Chris Rebert <c...(a)rebertia.com> wrote: > On Tue, Apr 27, 2010 at 2:58 PM, Chris Rebert <c...(a)rebertia.com> wrote: > > On Tue, Apr 27, 2010 at 2:42 PM, Michal M <mich.mier...(a)googlemail.com> wrote: > >> On 27 Kwi, 23:21, Duncan Booth <duncan.bo...(a)invalid.invalid> wrote: > >>> Michal M <mich.mier...(a)googlemail.com> wrote: > >>> > I've just found out that one of objects is not destroyed when it > >>> > should be. This means that something was holding reference to this > >>> > object or part of it (i.e. method). Is there any way to check what > >>> > holds that reference? I am unable to do that just looking to the code > >>> > or debugging it because it is pretty complicated, but I am able to > >>> > invoke this situation again. > > >>> See if this code helps: > > >>>http://groups.google.com/group/comp.lang.python/browse_thread/thread/.... > > >>> It's pretty old so it may need some adjustment, but I wrote it > >>> to figure out exactly that sort of problem. > > >> Thanks you for answers. > >> I tried to use gc.get_referrers(self) in point in code when according > >> to me object should be destroyed earlier but I did not see anything > >> interesting. Then just realised that gc will not destroy object even > >> when itself holds reference to his own method. > > >> For example > > >> class A(object): > >> def a(self): > >> pass > >> def b(self): > >> self.method = self.a > >> def __del__(self): > >> print "A object deleted" > > >>>> a = A() > >>>> del a > >> A object delted > >>>> a = A() > >>>> a.b() > >>>> del a > >> ... nothing ... > > >> I thought gc would discover such circle loops but apparently it did > >> not. > > > No, it does, you just didn't give it long enough; for performance > > reasons, cyclical GC is only done every so often: > > Addendum: > Also, defining __del__ in your example was likely problematic: > Seehttp://docs.python.org/library/gc.html#gc.garbage > > - Chris Thanks, specially for pointing the last issue with __del__ - I missed that!
From: Christian Heimes on 28 Apr 2010 08:59 Almar Klein wrote: > Ah, it does exist! I wish I knew that two months ago, it would've saved me > some precious time ;) The trick works only for objects that are tracked by CPython's garbage collector. Simple and non-containerish objects like str, int, unicode and some other types aren't tracked by the gc. IIRC all types written in Python are gc-aware. Christian
From: Marius Gedminas on 5 May 2010 15:46 On Apr 28, 3:59 pm, Christian Heimes <li...(a)cheimes.de> wrote: > The trick works only for objects that are tracked by CPython's garbage > collector. Simple and non-containerish objects like str, int, unicode > and some other types aren't tracked by the gc. Yes they are -- have you ever tried >>> import gc >>> gc.get_referrers(42) ? Marius Gedminas
From: Marius Gedminas on 5 May 2010 15:47
On Apr 27, 11:45 pm, Michal M <mich.mier...(a)googlemail.com> wrote: > I've just found out that one of objects is not destroyed when it > should be. This means that something was holding reference to this > object or part of it (i.e. method). Is there any way to check what > holds that reference? I am unable to do that just looking to the code > or debugging it because it is pretty complicated, but I am able to > invoke this situation again. I wrote http://pypi.python.org/pypi/objgraph for this purpose. -- Marius Gedminas |