I'm implementing a producer-consumer pattern in python using multiprocessing.Pool
and multiprocessing.Queue
. Consumers are pre-forked processes that uses gevent
to spawn multiple tasks.
Here is a trimmed down version of code:
import gevent
from Queue import Empty as QueueEmpty
from multiprocessing import Process, Queue, Pool
import signal
import time
# Task queue
queue = Queue()
def init_worker ():
# Ignore signals in worker
signal.signal( signal.SIGTERM, signal.SIG_IGN )
signal.signal( signal.SIGINT, signal.SIG_IGN )
signal.signal( signal.SIGQUIT, signal.SIG_IGN )
# One of the worker task
def worker_task1( ):
while True:
try:
m = queue.get( timeout = 2 )
# Break out if producer says quit
if m == 'QUIT':
print 'TIME TO QUIT'
break
except QueueEmpty:
pass
# Worker
def work( ):
gevent.joinall([
gevent.spawn( worker_task1 ),
])
pool = Pool( 2, init_worker )
for i in xrange( 2 ):
pool.apply_async( work )
try:
while True:
queue.put( 'Some Task' )
time.sleep( 2 )
except KeyboardInterrupt as e:
print 'STOPPING'
# Signal all workers to quit
for i in xrange( 2 ):
queue.put( 'QUIT' )
pool.join()
Now when I try to quit it, I get following state:
futex(0x7f99d9188000, FUTEX_WAIT, 0, NULL ...
.So what is the correct way to end such a process cleanly?
I figured out the problem. According to documentation for multiprocessing.Pool.join()
, pool
needs to be close()ed
before it can be join()ed
. Adding pool.close()
before pool.join()
solved the problem.