An attempt has been made to start a new process before the current process has finished its bootstrapping phase

Question

I am new to dask and I found so nice to have a module that makes it easy to get parallelization. I am working on a project where I was able to parallelize in a single machine a loop as you can see here . However, I would like to move over to dask.distributed. I applied the following changes to the class above:

diff --git a/mlchem/fingerprints/gaussian.py b/mlchem/fingerprints/gaussian.py
index ce6a72b..89f8638 100644
--- a/mlchem/fingerprints/gaussian.py
+++ b/mlchem/fingerprints/gaussian.py
@@ -6,7 +6,7 @@ from sklearn.externals import joblib
 from .cutoff import Cosine
 from collections import OrderedDict
 import dask
-import dask.multiprocessing
+from dask.distributed import Client
 import time


@@ -141,13 +141,14 @@ class Gaussian(object):
         for image in images.items():
             computations.append(self.fingerprints_per_image(image))

+        client = Client()
         if self.scaler is None:
-            feature_space = dask.compute(*computations, scheduler='processes',
+            feature_space = dask.compute(*computations, scheduler='distributed',
                                          num_workers=self.cores)
             feature_space = OrderedDict(feature_space)
         else:
             stacked_features = dask.compute(*computations,
-                                            scheduler='processes',
+                                            scheduler='distributed',
                                             num_workers=self.cores)

             stacked_features = numpy.array(stacked_features)

Doing so generates this error:

 File "/usr/local/Cellar/python/3.7.2_2/Frameworks/Python.framework/Versions/3.7/lib/python3.7/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()
                ...

I have tried different ways of adding if __name__ == '__main__': without any success. This can be reproduced by running this example. I would appreciate if anyone could help me to figure this out. I have no clue on how I should change my code to make it work.

Thanks.

Edit: The example is cu_training.py.

Answer 1

The Client command starts up new processes, so it will have to be within the if __name__ == '__main__': block as described in this SO question or this GitHub issue

This is the same as with the multiprocessing module