Paranoid Pirate worker in Python

#
## Paranoid Pirate worker
#
# Author: Daniel Lundin <dln(at)eintr(dot)org>
#

from random import randint
import time

import zmq

HEARTBEAT_LIVENESS = 3
HEARTBEAT_INTERVAL = 1
INTERVAL_INIT = 1
INTERVAL_MAX = 32

# Paranoid Pirate Protocol constants
PPP_READY = b"\x01" # Signals worker is ready
PPP_HEARTBEAT = b"\x02" # Signals worker heartbeat

def worker_socket(context, poller):
"""Helper function that returns a new configured socket
connected to the Paranoid Pirate queue"""

worker = context.socket(zmq.DEALER) # DEALER
identity = b"%04X-%04X" % (randint(0, 0x10000), randint(0, 0x10000))
worker.setsockopt(zmq.IDENTITY, identity)
poller.register(worker, zmq.POLLIN)
worker.connect("tcp://localhost:5556")
worker.send(PPP_READY)
return worker

context = zmq.Context(1)
poller = zmq.Poller()

liveness = HEARTBEAT_LIVENESS
interval = INTERVAL_INIT

heartbeat_at = time.time() + HEARTBEAT_INTERVAL

worker = worker_socket(context, poller)
cycles = 0
while True:
socks = dict(poller.poll(HEARTBEAT_INTERVAL * 1000))

# Handle worker activity on backend
if socks.get(worker) == zmq.POLLIN:
# Get message
# - 3-part envelope + content -> request
# - 1-part HEARTBEAT -> heartbeat
frames = worker.recv_multipart()
if not frames:
break # Interrupted

if len(frames) == 3:
# Simulate various problems, after a few cycles
cycles += 1
if cycles > 3 and randint(0, 5) == 0:
print("I: Simulating a crash")
break
if cycles > 3 and randint(0, 5) == 0:
print("I: Simulating CPU overload")
time.sleep(3)
print("I: Normal reply")
worker.send_multipart(frames)
liveness = HEARTBEAT_LIVENESS
time.sleep(1) # Do some heavy work
elif len(frames) == 1 and frames[0] == PPP_HEARTBEAT:
print("I: Queue heartbeat")
liveness = HEARTBEAT_LIVENESS
else:
print("E: Invalid message: %s" % frames)
interval = INTERVAL_INIT
else:
liveness -= 1
if liveness == 0:
print("W: Heartbeat failure, can't reach queue")
print("W: Reconnecting in %0.2fs…" % interval)
time.sleep(interval)

if interval < INTERVAL_MAX:
interval *= 2
poller.unregister(worker)
worker.setsockopt(zmq.LINGER, 0)
worker.close()
worker = worker_socket(context, poller)
liveness = HEARTBEAT_LIVENESS
if time.time() > heartbeat_at:
heartbeat_at = time.time() + HEARTBEAT_INTERVAL
print("I: Worker heartbeat")
worker.send(PPP_HEARTBEAT)