A worker is a unit of processing, that dequeues jobs and executes them.
It is started with a list of queues to listen to, in a specific order.
It can be started with concurrency options (multiple processes and / or multiple greenlets). We call this whole group a single 'worker' even though it is able to dequeue multiple jobs in parallel.
At any time, a worker is in one of these statuses:
init: General worker initialization
wait: Waiting for new jobs from Redis
spawn: Got some new jobs, greenlets are being spawned
full: All the worker pool is busy executing jobs
join: Waiting for current jobs to finish, no new one will be accepted
kill: Killing all current jobs
stop: Worker is stopped, no jobs should remain