Why this ref leak?

[Gerhard Häring]

import sys

def foo():
class C(object):
pass

foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
[9779 refs]

Both Python 2.4 and 2.5 don't clean up properly here. Why is this?
Aren't classes supposed to be garbage-collected?

-- Gerhard

 

[Bjoern Schliessmann]

Both Python 2.4 and 2.5 don't clean up properly here. Why is this?
Aren't classes supposed to be garbage-collected?

Yes, but not neccessarily immediately.

BTW, where is your method sys.gettotalrefcount supposed to come
from? My CPython doesn't have it.

Regards,


Björn

 

[Peter Otten]

import sys

def foo():
class C(object):
pass

foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
[9779 refs]

Both Python 2.4 and 2.5 don't clean up properly here. Why is this?
Aren't classes supposed to be garbage-collected?

The reference keeping the classes alive is probably object.__subclasses__():
2

Peter

 

[Thomas Heller]

import sys

def foo():
class C(object):
pass

foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
foo()
print ">>", sys.gettotalrefcount()
[9779 refs]

Both Python 2.4 and 2.5 don't clean up properly here. Why is this?
Aren't classes supposed to be garbage-collected?

-- Gerhard

Replace "foo()" with "foo(); gc.collect()" and the refcounts are stable.
Tested the python 2.6 from trunk.

Thomas

 

[Peter Otten]

The reference keeping the classes alive is probably
object.__subclasses__():

2

Oops, wrong guess:
1

Peter

 

[Peter Otten]

BTW, where is your method sys.gettotalrefcount supposed to come
from? My CPython doesn't have it.

It's in the debug build only.

Peter

 

[Bjoern Schliessmann]

Bjoern Schliessmann wrote:

It's in the debug build only.

Makes sense; thank you.

Regards,


Björn

 

[Duncan Booth]

Oops, wrong guess:

1

The list of subclasses is stored using weak references: that's why you have
to call a method to create a real list. What actually stops the class just
vapourising is its __mro__ attribute which creates a cycle, but the garbage
collector clears that up as you saw.