Pickle Exception.__cause__ and Exception.__traceback__

[crusaderky]

Closes #53

[codecov-io]

Codecov Report

Merging #54 into master will increase coverage by 0.92%.
The diff coverage is 95.34%.

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
+ Coverage   88.46%   89.38%   +0.92%     
==========================================
  Files           4        4              
  Lines         208      245      +37     
  Branches       29       42      +13     
==========================================
+ Hits          184      219      +35     
- Misses         15       16       +1     
- Partials        9       10       +1

Impacted Files	Coverage Δ
src/tblib/pickling_support.py	96.29% <95.34%> (-3.71%)	⬇️

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[crusaderky]

@ionelmc ready for review and merge

[crusaderky]

@ionelmc I've implemented all suggestions; ready for second review.
codecov is currently glitching as it seems to ignore several test suites (not the first time I see it).

[crusaderky]

@ionelmc any update?

Thanks

[ionelmc]

Ooooooof sorry, I'll look later today. Looks very good so far.

[ionelmc]

Very good, released v1.6.0 just now.

[blueyed]

I have not investigated, but this (c6d1796) causes test failures with pytest-parallel: kevlened/pytest-parallel#62

multiprocessing.managers.RemoteError:
---------------------------------------------------------------------------
Unserializable message: Traceback (most recent call last):
  File "/usr/lib/python3.8/multiprocessing/managers.py", line 298, in serve_client
    send(msg)
  File "/usr/lib/python3.8/multiprocessing/connection.py", line 206, in send
    self._send_bytes(_ForkingPickler.dumps(obj))
  File "/usr/lib/python3.8/multiprocessing/reduction.py", line 51, in dumps
    cls(buf, protocol).dump(obj)
_pickle.PicklingError: Can't pickle <function unpickle_exception at 0x7f67e4eb7040>: it's not the same object as tblib.pickling_support.unpickle_exception

[blueyed]

The workaround/fix is to move from tblib import pickling_support out of the Thread.run method: kevlened/pytest-parallel@be0975d

[ionelmc]

Would love to see some explanation on what's going on.

[crusaderky]

I, too, struggle to see how importing the module inside a slave thread can be any different from importing it in the main thread.

[blueyed]

Likely because install is doing more, and it might be the unpickle_exception from here? https://github.com/ionelmc/python-tblib/pull/54/files#diff-e61172fc1c18da0c20eef41cc3bbcd73R45

[crusaderky]

if you read the code, install isn't doing anything fancy at all, and unpickle_exception is a perfectly vanilla function defined at the top level of a globally-accessible Python module.