This change drops the memory used for Python processes run by Zulip in
development from about 1GB to 300MB on my laptop.
On the front of safety, http://pika.readthedocs.org/en/latest/faq.html
explains "Pika does not have any notion of threading in the code. If
you want to use Pika with threading, make sure you have a Pika
connection per thread, created in that thread. It is not safe to share
one Pika connection across threads.". Since this code only connects
to rabbitmq inside the individual threads, I believe this should be
safe.
Progress towards #32.
Importing zerver.worker.queue_processors (which is needed to get the list of
workers to start) is slow because it, in turn, imports a bunch of stuff. So we
move the process of starting up queue processing workers into another script
that gets started in parallel with everything else.
(imported from commit 839bada6dc7b93825c69b0d8fd9fbe2de75eabee)
Tim Abbott
Steven Oud
Anders Kaseorg
Zev Benjamin