Traceback when using multiprocessing, less than helpful?

John Ladasky john_ladasky at sbcglobal.net
Fri Nov 22 04:57:57 CET 2013


On Thursday, November 21, 2013 2:32:08 PM UTC-8, Ethan Furman wrote:
> Check out bugs.python.org.  Search for multiprocessing and tracebacks to see 
> if anything is already there; if not, create a new issue.


And on Thursday, November 21, 2013 2:37:13 PM UTC-8, Terry Reedy wrote:

> 1. Use 3.3.3 or latest 3.4 to see if there is any improvement in output.  
> I vaguely remember a tracker issue that might be related.


All right, there appear to be two recent bug reports which are relevant.

http://bugs.python.org/issue13831
http://bugs.python.org/issue17836

The comments in the first link, from Richard Oudkerk, appear to indicate that pickling an Exception (so that it can be sent between processes) is difficult, perhaps impossible.  I have never completely understood what can be pickled, and what cannot -- or, for that matter, why data needs to be pickled to pass it between processes. 

In any case, a string representation of the traceback can be pickled.  For debugging purposes, that can still help.  So, if I understand everything correctly, in this link...

http://hg.python.org/cpython/rev/c4f92b597074/

...Richard submits his "hack" (his description) to Python 3.4 which pickles and passes the string.  When time permits, I'll try it out.  Or maybe I'll wait, since Python 3.4.0 is still in alpha.



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