multiprocessing signal defect

[Neal Becker]

Adam Tauno Williams wrote:

> On Fri, 2010-10-29 at 08:12 -0400, Neal Becker wrote:
>> Seems multiprocessing doesn't behave well with signals:
>> ---------
>> from multiprocessing import Pool
>> import time
>> def sleep (dummy):
>>     time.sleep (10)
>> if __name__ == '__main__':
>>     pool = Pool (processes=2)
>>     result = pool.map (sleep, range (4))
>> -------------
>> start it up
>> $ python test_multip.py
>> ----------------------
>> ps auxf | grep python
>> nbecker   6605  1.6  0.1 338192  6952 pts/1    Sl+  08:03   0:00  |      
>> \_ python test_multip.py
>> nbecker   6606  0.0  0.1 186368  4760 pts/1    S+   08:03   0:00  |
>> \_ python test_multip.py
>> nbecker   6607  0.0  0.1 186372  4740 pts/1    S+   08:03   0:00  |
>> \_ python test_multip.py
>> kill 6607
>>  ps auxf | grep python
>> nbecker   6605  0.5  0.1 338192  6952 pts/1    Sl+  08:03   0:00  |      
>> \_ python test_multip.py
>> nbecker   6606  0.0  0.1 186368  4760 pts/1    S+   08:03   0:00  |
>> \_ python test_multip.py
>> nbecker   6607  0.0  0.0      0     0 pts/1    Z+   08:03   0:00  |
>> \_ [python] <defunct>
>>  kill 6606
>> ps auxf | grep python
>> nbecker   6605  0.3  0.1 338192  6952 pts/1    Sl+  08:03   0:00  |      
>> \_ python test_multip.py
>> nbecker   6606  0.0  0.0      0     0 pts/1    Z+   08:03   0:00  |
>> \_ [python] <defunct>
>> nbecker   6607  0.0  0.0      0     0 pts/1    Z+   08:03   0:00  |
>> \_ [python] <defunct>
>> Now we have 2 dead children and the parent is hung forever.
>> Isn't this a serious defect?
> 
> No, I think this is just POSIX/UNIX process behavior.  If the parent
> never joins on the child the child can never exit [which is what a
> Zombie process is].
> 
> For example, see the do_verify_workers method in
> 
<http://coils.hg.sourceforge.net/hgweb/coils/coils/file/6ab5ade3e488/src/coils/logic/workflow/services/executor.py>
> 
> A parent process needs to make some effort to reap its children.

Yes, and isn't this a defect in mulitprocessing module that the parent 
process does not reap its children in response to signals like show above?