"""
Least-recently used (LRU) queue device
Clients and workers are shown here in-process
Author: Guillaume Aubert (gaubert) <guillaume(dot)aubert(at)gmail(dot)com>
"""
import threading
import time
import zmq
NBR_CLIENTS = 10
NBR_WORKERS = 3
def worker_thread(worker_url, context, i):
""" Worker using REQ socket to do LRU routing """
socket = context.socket(zmq.REQ)
identity = "Worker-%d" % (i)
socket.setsockopt(zmq.IDENTITY, identity) #set worker identity
socket.connect(worker_url)
# Tell the borker we are ready for work
socket.send("READY")
try:
while True:
[address, empty, request] = socket.recv_multipart()
print("%s: %s\n" %(identity, request))
socket.send_multipart([address, "", "OK"])
except zmq.ZMQError, zerr:
# context terminated so quit silently
if zerr.strerror == 'Context was terminated':
return
else:
raise zerr
def client_thread(client_url, context, i):
""" Basic request-reply client using REQ socket """
socket = context.socket(zmq.REQ)
identity = "Client-%d" % (i)
socket.setsockopt(zmq.IDENTITY, identity) #Set client identity. Makes tracing easier
socket.connect(client_url)
# Send request, get reply
socket.send("HELLO")
reply = socket.recv()
print("%s: %s\n" % (identity, reply))
return
def main():
""" main method """
url_worker = "inproc://workers"
url_client = "inproc://clients"
client_nbr = NBR_CLIENTS
# Prepare our context and sockets
context = zmq.Context(1)
frontend = context.socket(zmq.ROUTER)
frontend.bind(url_client)
backend = context.socket(zmq.ROUTER)
backend.bind(url_worker)
# create workers and clients threads
for i in range(NBR_WORKERS):
thread = threading.Thread(target=worker_thread, args=(url_worker, context, i, ))
thread.start()
for i in range(NBR_CLIENTS):
thread_c = threading.Thread(target=client_thread, args=(url_client, context, i, ))
thread_c.start()
# Logic of LRU loop
# - Poll backend always, frontend only if 1+ worker ready
# - If worker replies, queue worker as ready and forward reply
# to client if necessary
# - If client requests, pop next worker and send request to it
# Queue of available workers
available_workers = 0
workers_list = []
# init poller
poller = zmq.Poller()
# Always poll for worker activity on backend
poller.register(backend, zmq.POLLIN)
# Poll front-end only if we have available workers
poller.register(frontend, zmq.POLLIN)
while True:
socks = dict(poller.poll())
# Handle worker activity on backend
if (backend in socks and socks[backend] == zmq.POLLIN):
# Queue worker address for LRU routing
message = backend.recv_multipart()
assert available_workers < NBR_WORKERS
worker_addr = message[0]
# add worker back to the list of workers
available_workers += 1
workers_list.append(worker_addr)
# Second frame is empty
empty = message[1]
assert empty == ""
# Third frame is READY or else a client reply address
client_addr = message[2]
# If client reply, send rest back to frontend
if client_addr != "READY":
# Following frame is empty
empty = message[3]
assert empty == ""
reply = message[4]
frontend.send_multipart([client_addr, "", reply])
client_nbr -= 1
if client_nbr == 0:
break # Exit after N messages
# poll on frontend only if workers are available
if available_workers > 0:
if (frontend in socks and socks[frontend] == zmq.POLLIN):
# Now get next client request, route to LRU worker
# Client request is [address][empty][request]
[client_addr, empty, request ] = frontend.recv_multipart()
assert empty == ""
# Dequeue and drop the next worker address
available_workers -= 1
worker_id = workers_list.pop()
backend.send_multipart([worker_id, "", client_addr, "", request])
#out of infinite loop: do some housekeeping
time.sleep (1)
frontend.close()
backend.close()
context.term()
if __name__ == "__main__":
main()