Multiprocessing / threading confusion

[Chris Angelico]

On Fri, Sep 6, 2013 at 5:27 AM, Paul Pittlerson <menkomigen6 at gmail.com> wrote:
> I'm trying to understand data handling using multiprocessing and threading, haven't gotten very far without running into problems. This is my code:
>
>
> What I expect to happen is the Debugger object will receive one string at a time, and read it from the queue. But that's not what I see the the output, the "started worker" stuff seems to print for every process, but "ticked" and "exited" will show up in unpredictable ways, I'm guessing they overwrite each other and therefore will not always appear in the output.
>
> So I'm looking for help in trying to make sense of this kind of stuff, I thought this was the basic functionality that Queue() would take care of unless there is some other problem in my code.

The first thing I notice is that your Debugger will quit as soon as
its one-secondly poll results in no data. This may or may not be a
problem for your code, but I'd classify it as code smell at best. Is
your goal here to make sure Debugger doesn't stop your process from
exiting? If so, a simpler and safer solution is to make it a daemon
thread.

The other thing I see here is your use of __del__ to print your exit
message. I don't know if Thread objects are involved in reference
loops, but if they are, __del__ (probably) won't be called immediately
on thread termination.

Your subprocesses are a little odd; they spin off another thread, then
halt the first thread. Why not simply do the work in the first thread?
You then treat the thread's __del__ method as the process's death,
which isn't strictly true, but probably close enough.

ChrisA