How to fix _wait_for_tstate_lock
If we ever try to exit server with objects in the Multiprocessing Queue, we could
end up in a race condition that causes a deadlock with _wait_for_tstate_lock.
One way to avoid it is to clear the queue before exit.
Debugging
To figure out which queue is not empty,
import multiprocessing
import inspect
# initialize a queue
q = multiprocessing.Queue(10)
# get function where the queue is created or where we are adding objects to queue
# so that we can identify which queue it is
caller = inspect.getframeinfo(inspect.stack()[1][0])
thread_name = f"MultiQueue_{caller.filename}:{caller.lineno}"
# add new object
q.put("hello")
# set thread name
q._thread.name = thread_name
QueueFeederThread is stared after you put an object into the queue.
After the first time you put an object into the queue, you can set a name to the thread.
You can then use py-spy to figure out which thread is preventing your program from exiting.
py-spy dump -p <pid>