[Python-Dev] [Python-checkins] Daily reference leaks (d7e490db8d54): sum=61494

[Benjamin Peterson]

On Tue, Oct 20, 2015, at 15:57, Antoine Pitrou wrote:
> 
> > These leaks have been here a while. Anyone know the cause?
> > 
> > On Tue, 20 Oct 2015 at 01:47 <solipsis at pitrou.net> wrote:
> > 
> >> results for d7e490db8d54 on branch "default"
> >> --------------------------------------------
> >>
> >> test_capi leaked [5411, 5411, 5411] references, sum=16233
> >> test_capi leaked [1421, 1423, 1423] memory blocks, sum=4267
> >> test_functools leaked [0, 2, 2] memory blocks, sum=4
> >> test_threading leaked [10820, 10820, 10820] references, sum=32460
> >> test_threading leaked [2842, 2844, 2844] memory blocks, sum=8530
> 
> Bisection shows they were probably introduced by:
> 
> changeset:   97413:dccc4e63aef5
> user:        Raymond Hettinger <python at rcn.com>
> date:        Sun Aug 16 19:43:34 2015 -0700
> files:       Doc/library/operator.rst Doc/whatsnew/3.6.rst
> Lib/operator.py Lib/test/test_operator.py
> description:
> Issue #24379: Add operator.subscript() as a convenience for building
> slices.
> 
> 
> If you comment out `@object.__new__` on line 411 in operator.py, or if
> you remove the __slots__ assignment (which is a bit worrying), the leak
> seems suppressed.

The problem is that the "subscript" class is not a GC type, but
participates in a cycle through its type. I suspect it's type to force
all heap types to have GC. Armin Rigo found previous examples where this
special case caused problems, and I don't see what it buys anyway.