Runtime error using keras fit_generator with multiprocessing

Question

Hi i am trying to use fit_generator in keras (windows 10, latest keras version, gtx 1060) but when i toggle use_multiprocessing to true the program freezes and this error pops out:

Epoch 1/1
Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\ProgramData\Anaconda3\lib\threading.py", line 916, in _bootstrap_inner
    self.run()
  File "C:\ProgramData\Anaconda3\lib\threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "C:\ProgramData\Anaconda3\lib\site-packages\keras\utils\data_utils.py", line 548, in _run
    with closing(self.executor_fn(_SHARED_SEQUENCES)) as executor:
  File "C:\ProgramData\Anaconda3\lib\site-packages\keras\utils\data_utils.py", line 522, in <lambda>
    initargs=(seqs,))
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 119, in Pool
    context=self.get_context())
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 174, in __init__
    self._repopulate_pool()
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\pool.py", line 239, in _repopulate_pool
    w.start()
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
    prep_data = spawn.get_preparation_data(process_obj._name)
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
    _check_not_importing_main()
  File "C:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 136, in _check_not_importing_main
    is not going to be frozen to produce an executable.''')
RuntimeError:
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

    This probably means that you are not using fork to start your
    child processes and you have forgotten to use the proper idiom
    in the main module:

        if __name__ == '__main__':
            freeze_support()
            ...

    The "freeze_support()" line can be omitted if the program
    is not going to be frozen to produce an executable.

When I train it without multiprocessing no error occurs.

Possible duplicate of [python multiprocessing on windows, if \_\_name\_\_ == "\_\_main\_\_"](https://stackoverflow.com/questions/20222534/python-multiprocessing-on-windows-if-name-main) — the-lay, Sep 17 '18 at 13:11

score 1 · Answer 1 · answered Sep 17 '18 at 13:10

This is essentially the same question as python multiprocessing on windows, if __name__ == "__main__"

Since Windows has no fork, the multiprocessing module starts a new Python process and imports the calling module. Without __name__ == __main__ idiom the new process (started by keras' fit_generator()) will call your all code again and will start another process, and so on ad infinitum (until OOM).

You have to put the initial code into main and the multiprocessing part outside.

Runtime error using keras fit_generator with multiprocessing

1 Answers1