New submission from STINNER Victor:
While trying to reproduce a race condition in asyncio, I got an assertion error
from the Python garbage collector at exit. It's not easy to reproduce the
issue: run attached script on Python 3.4 compiled in debug mode (to get
assertions) and press CTRL+c twice. It looks like the bug occurs more often
after at least 400 runs.
The Future class of the asyncio may store an exception in its private
Future._exception attribute. An exception stores a traceback. I don't know if
it's related.
Output:
---
...
run #347
^CTraceback (most recent call last):
File "x.py", line 73, in <module>
main()
File "x.py", line 70, in main
el.join()
File "/home/haypo/prog/python/default/Lib/threading.py", line 1061, in join
self._wait_for_tstate_lock()
File "/home/haypo/prog/python/default/Lib/threading.py", line 1077, in
_wait_for_tstate_lock
elif lock.acquire(block, timeout):
run #348
KeyboardInterrupt
...
run #364
run #365
run #366
run #367
-cancelled-
run #368
^CException ignored in: <module 'threading' from
'/home/haypo/prog/python/default/Lib/threading.py'>
Traceback (most recent call last):
File "/home/haypo/prog/python/default/Lib/threading.py", line 1295, in
_shutdown
t.join()
File "/home/haypo/prog/python/default/Lib/threading.py", line 1061, in join
self._wait_for_tstate_lock()
File "/home/haypo/prog/python/default/Lib/threading.py", line 1077, in
_wait_for_tstate_lock
elif lock.acquire(block, timeout):
KeyboardInterrupt
-cancelled-
python: Modules/gcmodule.c:379: visit_decref: Assertion `((gc)->gc.gc_refs >>
(1)) != 0' failed.
Abandon (core dumped)
$ ls *core
python-6564.core
$ gdb ./python -c python-6564.core
Core was generated by `./python x.py'.
Program terminated with signal SIGABRT, Aborted.
(gdb) where
#0 0x0000003f3a835c59 in raise () from /lib64/libc.so.6
#1 0x0000003f3a837368 in abort () from /lib64/libc.so.6
#2 0x0000003f3a82ebb6 in __assert_fail_base () from /lib64/libc.so.6
#3 0x0000003f3a82ec62 in __assert_fail () from /lib64/libc.so.6
#4 0x000000000043ac66 in visit_decref (
op=Frame 0x7f013c001398, for file x.py, line 43, in task
(self=<WorkerThread(_kwargs={}, loop=<_UnixSelectorEventLoop(_scheduled=[],
_default_executor=None, _running=True, _ready=<collections.deque at remote
0x7f014bbed6e0>,
_selector=<EpollSelector(_map=<_SelectorMapping(_selector=<...>) at remote
0x7f014c3bff60>, _epoll=<select.epoll at remote 0x7f014d5bce08>, _fd_to_key={5:
<SelectorKey at remote 0x7f014bbecaf8>}) at remote 0x7f014c3bfae8>,
_granularity=<float at remote 0x7f014e8c76b8>, _ssock=<socket at remote
0x7f014c3c5a78>, _internal_fds=1, _csock=<socket at remote 0x7f014bbeb5f8>,
_signal_handlers={}) at remote 0x7f014c437400>, _is_stopped=False,
_target=None, _daemonic=False, executor=<ThreadPoolExecutor(_max_workers=5,
_shutdown=False, _work_queue=<Queue(not_empty=<Condition(release=<built-in
method release of _thread.lock object at remote 0x7f014c3bb1a0>,
acquire=<built-in method acquire of _thread.lock object at remote
0x7f014c3bb1a0>, _lock=<_thread.lock at remote 0x
7f014c3bb1a0>, _waiters=<collecti...(truncated), data=0x0) at
Modules/gcmodule.c:379
#5 0x00000000004336bd in tb_traverse (tb=0x7f01493a66e8, visit=0x43abb4
<visit_decref>, arg=0x0) at Python/traceback.c:64
#6 0x000000000043acdc in subtract_refs (containers=0x8f1a20 <generations+64>)
at Modules/gcmodule.c:398
#7 0x000000000043bdee in collect (generation=2, n_collected=0x7fff499317c0,
n_uncollectable=0x7fff499317b8, nofail=0)
at Modules/gcmodule.c:957
#8 0x000000000043c455 in collect_with_callback (generation=2) at
Modules/gcmodule.c:1128
#9 0x000000000043d1d5 in PyGC_Collect () at Modules/gcmodule.c:1604
#10 0x000000000041e959 in Py_Finalize () at Python/pythonrun.c:605
#11 0x000000000043a890 in Py_Main (argc=2, argv=0x22bb020) at Modules/main.c:771
#12 0x000000000041aba9 in main (argc=2, argv=0x7fff49931ab8) at
./Modules/python.c:69
(gdb) frame 4
#4 0x000000000043ac66 in visit_decref (
(gdb) print op
$3 = Frame 0x7f013c001398, for file x.py, line 43, in task
(self=<WorkerThread(_kwargs={}, loop=<_UnixSelectorEventLoop(_scheduled=[],
_default_executor=None, _running=True, _ready=<collections.deque at remote
0x7f014bbed6e0>,
_selector=<EpollSelector(_map=<_SelectorMapping(_selector=<...>) at remote
0x7f014c3bff60>, _epoll=<select.epoll at remote 0x7f014d5bce08>, _fd_to_key={5:
<SelectorKey at remote 0x7f014bbecaf8>}) at remote 0x7f014c3bfae8>,
_granularity=<float at remote 0x7f014e8c76b8>, _ssock=<socket at remote
0x7f014c3c5a78>, _internal_fds=1, _csock=<socket at remote 0x7f014bbeb5f8>,
_signal_handlers={}) at remote 0x7f014c437400>, _is_stopped=False,
_target=None, _daemonic=False, executor=<ThreadPoolExecutor(_max_workers=5,
_shutdown=False, _work_queue=<Queue(not_empty=<Condition(release=<built-in
method release of _thread.lock object at remote 0x7f014c3bb1a0>,
acquire=<built-in method acquire of _thread.lock object at remote
0x7f014c3bb1a0>, _lock=<_thread.lock at remote 0x7f
014c3bb1a0>, _waiters=<collecti...(truncated)
---
----------
messages: 210368
nosy: gvanrossum, haypo, pitrou, serhiy.storchaka
priority: normal
severity: normal
status: open
title: python: Modules/gcmodule.c:379: visit_decref: Assertion
`((gc)->gc.gc_refs >> (1)) != 0' failed.
type: crash
versions: Python 3.4
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<http://bugs.python.org/issue20526>
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