`parfor` doesn't seem to work with Python lists

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Hagai Hargil
Hagai Hargil 2016-10-10
评论： Robert Snoeberger 2016-10-12
Hellp everyone,
I'm trying to use a parfor loop that includes a Python list as an input argument to a class array:
allEvents(1:size(hexData, 2), 1) = Event();
parfor n = 1:size(hexData, 2)
allEvents(n) = createSingleEvent(hexData{n}, dataFormat, range, hexToBinMap);
end
where hexData{n} is the mentioned Python list, and allEvents is a preallocated array of class Event() (value class, not handle).
Unfortunately, no matter how I turn it, the parfor loop won't run. Needless to say, a regular for loop compiles properly.
The error I receive is a "Python error: Index exceeds list dimensions". When I manually check possibly-problematic indices I recieve no such error.
By adding a "char(hexData{n})" inside the parfor I receive "Index exceeds matrix dimensions" in the first occasion inside the function where I need to use the hexData{n} value, even if I see that the index definitely exists in that variable:
startOfString = hexDataAsChar(1); % This errors out
Only when I erase all traces that hexData was ever a Python list does MATLAB kindly allows me to parfor this loop.
Any help will be deeply appreciated. Thanks!

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Robert Snoeberger
Robert Snoeberger 2016-10-11
If you are using a parpool, then parfor needs to save and load the Python list. Saving (serializing) Python objects into a MAT-file is listed as a limitation .
  2 个评论
Hagai Hargil
Hagai Hargil 2016-10-12
Dear Robert, Thank you for your quick reply. I wasn't aware that this 'save and load' process occurs during the parfor loop. Is there a workaround around this limitation, which can enable me to parallelize processing of Python objects?
Robert Snoeberger
Robert Snoeberger 2016-10-12
Unfortunately, I'm not aware of a workaround.
The only idea that I can think of is to wrap the Python object in your own MATLAB class with customized save and load . You might be able to use pickle to do the serialization. I haven't tried it so I don't know if the idea is viable.

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