Script globals in a GC cycle not finalized when exiting with SystemExit

[encukou]

BPO	24596
Nosy	@ncoghlan, @pitrou, @encukou, @ZackerySpytz
PRs	bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit #7918 [3.6] bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit (GH-7918) #8069 [3.7] bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit (GH-7918) #8070

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2018-07-03.20:18:03.556>
created_at = <Date 2015-07-09.13:31:32.739>
labels = ['interpreter-core', '3.7', '3.8']
title = 'Script globals in a GC cycle not finalized when exiting with SystemExit'
updated_at = <Date 2018-07-03.20:18:03.555>
user = 'https://github.com/encukou'

bugs.python.org fields:

activity = <Date 2018-07-03.20:18:03.555>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2018-07-03.20:18:03.556>
closer = 'pitrou'
components = ['Interpreter Core']
creation = <Date 2015-07-09.13:31:32.739>
creator = 'petr.viktorin'
dependencies = []
files = []
hgrepos = []
issue_num = 24596
keywords = ['patch']
message_count = 6.0
messages = ['246491', '246498', '246502', '321001', '321003', '321004']
nosy_count = 4.0
nosy_names = ['ncoghlan', 'pitrou', 'petr.viktorin', 'ZackerySpytz']
pr_nums = ['7918', '8069', '8070']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue24596'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[encukou]

When this program is invoked as a script (python reproducer.py), the del is never called:

---

class ClassWithDel:
    def __del__(self):
        print('__del__ called')

a = ClassWithDel()
a.link = a

raise SystemExit(0)

---

Raising a different exception, moving the code to a function, importing the module, or invoking with -m (or even -c), causes __del__ to be called normally.

[pitrou]

It's likely that your global variable gets caught in the traceback attached to the SystemExit, and that either never gets deallocated, or gets deallocated too late.

[pitrou]

Actually, the problem is in PyRun_SimpleFileExFlags(). The executed module is decref'ed after calling PyErr_Print(), but the latter never returns when the exception is a SystemExit.

[pitrou]

New changeset d8cba5d by Antoine Pitrou (Zackery Spytz) in branch 'master':
bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit (GH-7918)
d8cba5d

[pitrou]

New changeset 20ae4c6 by Antoine Pitrou (Miss Islington (bot)) in branch '3.7':
bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit (GH-7918) (GH-8070)
20ae4c6

[pitrou]

New changeset e1ebf51 by Antoine Pitrou (Miss Islington (bot)) in branch '3.6':
bpo-24596: Decref module in PyRun_SimpleFileExFlags() on SystemExit (GH-7918) (GH-8069)
e1ebf51