Race condition during pickle.load()

[papadp]

BPO	36773
Nosy	@ronaldoussoren, @pitrou, @taleinat, @serhiy-storchaka, @papadp
Files	reproduce.tar.gz

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

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GitHub fields:

assignee = None
closed_at = <Date 2019-08-05.08:26:43.132>
created_at = <Date 2019-05-02.08:24:59.927>
labels = ['3.7', 'library', 'type-crash']
title = 'Race condition during pickle.load()'
updated_at = <Date 2019-08-05.08:26:43.119>
user = 'https://github.com/papadp'

bugs.python.org fields:

activity = <Date 2019-08-05.08:26:43.119>
actor = 'taleinat'
assignee = 'none'
closed = True
closed_date = <Date 2019-08-05.08:26:43.132>
closer = 'taleinat'
components = ['Library (Lib)']
creation = <Date 2019-05-02.08:24:59.927>
creator = 'papad'
dependencies = []
files = ['48294']
hgrepos = []
issue_num = 36773
keywords = []
message_count = 5.0
messages = ['341257', '341265', '341424', '341431', '349035']
nosy_count = 5.0
nosy_names = ['ronaldoussoren', 'pitrou', 'taleinat', 'serhiy.storchaka', 'papad']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue36773'
versions = ['Python 3.7']

[papadp]

There seems to be a race condition when unpickling the same object from different threads (My guess is it's related to imports that are related to the unpickled object).

I have used the following files for reproduction (File contents are in the attached archive, also pasted at the bottom of the issue report):
import_me.py - Containing the object we will pickle
pickle_object.py - the code to pickle the object
trigger.py - a piece of code to unpickle the object from different threads simultaneously and trigger the crash

I have used the files in the attached archive (containing the 3 files mentioned above)

to reproduce run the following commands:

pickle_object.py
trigger.py

Running trigger.py will crash on about 50% of the runs with the following error:

Traceback (most recent call last):
  File "./trigger.py", line 16, in pickle_load_thread
    pickle.load(h)
AttributeError: Can't get attribute 'PickleMe' on <module 'import_me' from '/data/import_me.py'>

I have tested this on the following software stacks:

1. python:3.7.3 docker

   • linux version: 4.15.0-48-generic bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations #51-Ubuntu SMP Wed Apr 3 08:28:49 UTC 2019 x86_64 GNU/Linux
   • python: 3.7.3
   • distro: Debian GNU/Linux 9 (stretch)

2. my laptop

   • linux version: 4.15.0-48-generic bpo-28598: Support __rmod__ for RHS subclasses of str in % string formatting operations #51-Ubuntu SMP Wed Apr 3 08:28:49 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
   • python: 3.6.7
   • distro: Ubuntu 18.04.2 LTS

I'm uncertain if this is a bug related to pickle or python module importing.
Similar issues I've found: https://bugs.python.org/issue12680 and https://bugs.python.org/issue30891.

---------------------------------------------------------------------------------------
filename: import_me.py
#! /usr/bin/python3

class PickleMe(object):

    def __init__(self):
        self.a = "a"

---

filename: pickle_object.py
#! /usr/bin/python3

import pickle
from import_me import PickleMe

p = PickleMe()

with open('pickled', 'wb') as h:
    pickle.dump(p, h)

---

filename: trigger.py
#! /usr/bin/python3

import threading
import pickle

import logging

threads = []

def pickle_load_thread():

    logging.error("Thread %d loading", threading.get_ident())

try:
    with open('pickled', 'rb') as h:
        pickle.load(h)
except:
    logging.exception("Exception in loading")

def start_pickle_load_thread():

    for x in range(2):
        load_thread = threading.Thread(target=pickle_load_thread)
        load_thread.daemon = True
        threads.append(load_thread)

    for x in threads:
        x.start()


if __name__ == '__main__':

    start_pickle_load_thread()

    for t in threads:
        t.join()

[ronaldoussoren]

This could be a duplicate of bpo-34572

[papadp]

In what version should this be fixed? I see https://bugs.python.org/issue34572 says the fix is in version 3.7, while I'm experiencing this on python 3.7.3, which version should I check?

[serhiy-storchaka]

It should be fixed in 3.7.3.

https://docs.python.org/3.7/whatsnew/changelog.html#python-3-7-3-release-candidate-1

[taleinat]

On Windows 10, this reproduces consistently with 3.6 and 3.7.0, but not with 3.7.4, 3.8.0b3 and current master. So this definitely seems to be fixed.