New submission from Dan Snider <mr.assume.a...@gmail.com>:
Sort of because I'm really not sure if it's working as intended or not. When I
found this out today, I noticed that the documentation of `exec` has been
updated since the last time I saw it, which is good, but it still leaves much
to be desired. Specifically, I don't feel it does enough to explain the
supposed justification for `exec`'s ability to very easily trigger a
catastrophic memory leak someone unfamiliar with the code they're working on
may never have the patience (if not time) to track down..
An illustration:
import itertools
import sys
import weakref
def noleak():
def outer():
from itertools import repeat as reeeee
def f():
return reeeee(1, 1)
return f
f = outer()
c = sys.getrefcount(f)
return c, weakref.ref(f), sys.getrefcount(itertools.repeat)
def leaks():
ns = {}
co = ('from itertools import repeat as reeeee\n'
'def f(): return reeeee(1, 1)')
pre = sys.getrefcount(ns)
exec(co, ns)
pos = sys.getrefcount(ns)
return (pre, pos), weakref.ref(ns['f']),
sys.getrefcount(itertools.repeat)
for i in range(10):
leaks()
for i in range(10):
noleak()
Perhaps I'm wrong in thinking that this is behaving as intended and it actually
is a bug. Starting from builtin_exec_impl I got as far as _PyFrame_New_NoTrack
before I threw up my hands and decided this is something for someone else.
If `exec` with only a `globals` argument is indeed working as intended, I still
think it's ridiculous that every item added to that dict has an "extra",
non-obvious reference count that is impossible to vanquish of from within
Python. I intuited leaving `locals` blank will do what usually happens when
functions take optional arguments, and *usually* that is *not* the triggering
of a "hidden" memory leak.
Perhaps the only solution here is to deprecate `exec` accepting `globals` and
`locals` as optional arguments.
----------
assignee: docs@python
components: Documentation, Interpreter Core
messages: 319157
nosy: bup, docs@python
priority: normal
severity: normal
status: open
title: exec() maybe has a memory leak
versions: Python 3.6, Python 3.7
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue33814>
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