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PenghuiCheng
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Sep 11, 2018
Summary:
`Process.start()` actually take some time as it needs to start a
process and pass the arguments over via a pipe. Therefore, we
only add a worker to self.workers list after it started, so
that we do not call `.join()` if program dies before it starts,
and `__del__` tries to join it but will get:
AssertionError: can only join a started process.
Example trace when such error happens:
```py
[unrelated]
File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 500, in __iter__
return _DataLoaderIter(self)
File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 292, in __init__
w.start()
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/process.py", line 112, in start
self._popen = self._Popen(self)
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/context.py", line 223, in _Popen
return _default_context.get_context().Process._Popen(process_obj)
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/context.py", line 277, in _Popen
return Popen(process_obj)
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/popen_fork.py", line 20, in __init__
self._launch(process_obj)
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/popen_fork.py", line 70, in _launch
self.pid = os.fork()
KeyboardInterrupt
Exception ignored in: <function _DataLoaderIter.__del__ at 0x7fa704d5aa60>
Traceback (most recent call last):
File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 398, in __del__
self._shutdown_workers()
File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 392, in _shutdown_workers
w.join()
File "/private/home/ssnl/miniconda3/lib/python3.7/multiprocessing/process.py", line 139, in join
assert self._popen is not None, 'can only join a started process'
AssertionError: can only join a started process
```
No test because hard to reliably trigger.
Pull Request resolved: pytorch#11432
Reviewed By: ezyang
Differential Revision: D9735430
Pulled By: SsnL
fbshipit-source-id: a8912d9bb4063f210d6236267b178173810e2351
facebook-github-bot
pushed a commit
that referenced
this pull request
Sep 13, 2018
Summary: Same reason as in #11432 . Example error: ``` Exception ignored in: <function _DataLoaderIter.__del__ at 0x7fa06963cf28> Traceback (most recent call last): File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 405, in __del__ self._shutdown_workers() File "/private/home/ssnl/miniconda3/lib/python3.7/site-packages/torch/utils/data/dataloader.py", line 401, in _shutdown_workers self.pin_memory_thread.join() AttributeError: '_DataLoaderIter' object has no attribute 'pin_memory_thread' ``` Pull Request resolved: #11599 Differential Revision: D9801143 Pulled By: SsnL fbshipit-source-id: 520590a21f56fa381fcac621457a7544d3fba47e
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Process.start()actually take some time as it needs to start aprocess and pass the arguments over via a pipe. Therefore, we
only add a worker to self.workers list after it started, so
that we do not call
.join()if program dies before it starts,and
__del__tries to join it but will get:AssertionError: can only join a started process.
Example trace when such error happens:
No test because hard to reliably trigger.