Valentyn Tymofieiev created BEAM-8651:
-----------------------------------------
Summary: Python 3 portable pipelines sometimes fail with errors in
StockUnpickler.find_class()
Key: BEAM-8651
URL: https://issues.apache.org/jira/browse/BEAM-8651
Project: Beam
Issue Type: Sub-task
Components: sdk-py-core
Reporter: Valentyn Tymofieiev
Several Beam users [1,2] reported an error which happens on Python 3 in
StockUnpickler.find_class.
So far I've seen reports of the error on Python 3.5, 3.6, and 3.7.1, on Flink
and Dataflow runners. On Dataflow runner so far I have seen this in streaming
pipelines only, which use portable SDK worker.
Typical stack trace:
{noformat}
File "python3.5/site-packages/apache_beam/runners/worker/bundle_processor.py",
line 1148, in _create_pardo_operation
dofn_data = pickler.loads(serialized_fn)
File "python3.5/site-packages/apache_beam/internal/pickler.py", line 265, in
loads
return dill.loads(s)
File "python3.5/site-packages/dill/_dill.py", line 317, in loads
return load(file, ignore)
File "python3.5/site-packages/dill/_dill.py", line 305, in load
obj = pik.load()
File "python3.5/site-packages/dill/_dill.py", line 474, in find_class
return StockUnpickler.find_class(self, module, name)
AttributeError: Can't get attribute 'ClassName' on <module 'ModuleName' from
'python3.5/site-packages/filename.py'>
{noformat}
According to Guenther from [1]:
{quote}
This looks exactly like a race condition that we've encountered on Python
3.7.1: There's a bug in some older 3.7.x releases that breaks the
thread-safety of the unpickler, as concurrent unpickle threads can access a
module before it has been fully imported. See
https://bugs.python.org/issue34572 for more information.
The traceback shows a Python 3.6 venv so this could be a different issue
(the unpickle bug was introduced in version 3.7). If it's the same bug then
upgrading to Python 3.7.3 or higher should fix that issue. One potential
workaround is to ensure that all of the modules get imported during the
initialization of the sdk_worker, as this bug only affects imports done by
the unpickler.
{quote}
Opening this for visibility. Current open questions are:
1. Find a minimal example to reproduce this issue.
2. Figure out whether users are still affected by this issue on Python 3.7.3.
3. Communicate a workarounds for 3.5, 3.6 users affected by this.
[1]
https://lists.apache.org/thread.html/5581ddfcf6d2ae10d25b834b8a61ebee265ffbcf650c6ec8d1e69408@%3Cdev.beam.apache.org%3E
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