multiprocessing Pool workers cannot create subprocesses

[Jason Grout]

On 3/18/11 3:29 PM, Ned Deily wrote:
> In article<4D838D28.5090705 at creativetrax.com>,
>   Jason Grout<jason-python at creativetrax.com>  wrote:
>> The problem appears to be that multiprocessing sets its workers to have
>> the daemon flag set to True, which prevents workers from creating child
>> processes.  If I uncomment the line indicated in the code, I can create
>> child processes and the program works (it prints out the even numbers
>> from 0 to 18).
>>
>> It makes me nervous to just change the daemon status of the process like
>> that, especially when I don't know the reason the workers have
>> daemon=True to begin with.  What is the reasoning behind that decision?
>>    What issues do we need to worry about if we just set the daemon mode
>> flag like in the above code?
>
> http://docs.python.org/library/multiprocessing.html#multiprocessing.Proce
> ss.daemon
>
> "When a process exits, it attempts to terminate all of its daemonic
> child processes.
>
> Note that a daemonic process is not allowed to create child processes.
> Otherwise a daemonic process would leave its children orphaned if it
> gets terminated when its parent process exits. Additionally, these are
> not Unix daemons or services, they are normal processes that will be
> terminated (and not joined) if non-daemonic processes have exited."
>

Right; thanks.  Let me rephrase my questions:

1. Why is important that the multiprocessing Pool worker processors have 
daemon=True (I think this is the same as asking: why is it important 
that they be terminated with terminate() rather than join() )?

2. Is it safe for us to reset a Pool worker process to have daemon=False 
before starting a subprocess from that worker, like in the code from the 
original message?

Thanks,

Jason