前一段时间2014北京PyCon大会吐槽颇多，所以我就到InfoQ上找了找2013的大会视频，对网络射击手游High Noon 2基于Python的服务器架构的视频挺感兴趣，尤其是游戏服务器中的0 downtime，原理他们底层不是原生的socket，
而是基于ZeroMq的socket,由于ZeroMq的短线自动重连可以满足游戏服务器的热启动，不需要代码层面的热启动，热更新，当更新代码完成后直接重启服务器，之前未处理的请求会继续处理。瞬间觉得非常高大上，于是最近一段时间回家一直研究ZeroMq，在guide的LRU这边停留了较长时间，本篇就是谈谈ZeroMq LRU算法中间件。
对普通的请求回复代理，也就是使用了ROUTER-DEALER模式比较好理解，但这种方式有个天生缺点，DEALER会使用负载均衡的方式将客户端的请求转发给服务器端，由于服务器的处理能力各不相同，就会导致有些服务器很忙，有些很闲，这不是我们想看到的，我们希望能压榨所有服务器能力，所以就出现了通用型的LRU算法。
这里使用ROUTER-ROUTER模式，刚开始你可能很诧异，且听我慢慢道来。
那如何能充分使用每台服务器性能呢？
1.当woker启动时告诉backend自己已准备好，将该worker加入work_queue可用队列中
2.当client请求时，从work_queue中取出一个work，把请求交给该work处理
3.当work处理好后把响应发给client，并把自己再次加入到work_queue中
也就是使用work队列，记录可用work，只要work完成请求就代表已空闲，再次加入work队列。
那为什么backend需要使用ROUTER模式呢？关键点是当我要把client来的请求发给固定的work，而只有ROUTER模式具有路由标识功能，明白了这点，代码也就容易了。
"""
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>
"""
from __future__ import print_function
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
work的响应消息格式为
--------------------
|Frame0| Client-idntity
--------------------
|Frame1|
--------------------
|Frame2| OK
"""
socket = context.socket(zmq.REQ)
# Set the worker identity
socket.identity = (u"Worker-%d" % (i)).encode(‘ascii‘)
socket.connect(worker_url)
# Tell the borker we are ready for work
socket.send(b"READY")
try:
while True:
address = socket.recv()
empty = socket.recv()
request = socket.recv()
print("%s: %s\n" % (socket.identity.decode(‘ascii‘), request.decode(‘ascii‘)), end=‘‘)
socket.send(address, zmq.SNDMORE)
socket.send(b"", zmq.SNDMORE)
socket.send(b"OK")
except zmq.ContextTerminated:
# context terminated so quit silently
return
def client_thread(client_url, context, i):
""" Basic request-reply client using REQ socket
client的消息格式为
--------------------
|Frame0| Client-1
--------------------
|Frame1|
--------------------
|Frame2| HELLO
"""
socket = context.socket(zmq.REQ)
socket.identity = (u"Client-%d" % (i)).encode(‘ascii‘)
socket.connect(client_url)
# Send request, get reply
socket.send(b"HELLO")
reply = socket.recv()
print("%s: %s\n" % (socket.identity.decode(‘ascii‘), reply.decode(‘ascii‘)), end=‘‘)
def main():
""" main method """
url_worker = "inproc://workers"
url_client = "inproc://clients"
client_nbr = NBR_CLIENTS
# Prepare our context and sockets
context = zmq.Context()
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
worker_addr = backend.recv()
assert available_workers < NBR_WORKERS
# add worker back to the list of workers
available_workers += 1
workers_list.append(worker_addr)
# Second frame is empty
empty = backend.recv()
assert empty == b""
# Third frame is READY or else a client reply address
client_addr = backend.recv()
# If client reply, send rest back to frontend
if client_addr != b"READY":
# Following frame is empty
empty = backend.recv()
assert empty == b""
reply = backend.recv()
frontend.send(client_addr, zmq.SNDMORE)
frontend.send(b"", zmq.SNDMORE)
frontend.send(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 = frontend.recv()
empty = frontend.recv()
assert empty == b""
request = frontend.recv()
# Dequeue and drop the next worker address
available_workers -= 1
worker_id = workers_list.pop()
"""worker_id就是work的标识，也就是需要发给worker_id，所以backend需要使用ROUTER模式
在所有消息之间zmq需要一个空消息作为标识，当work接受到请求时会直接读到第一个空消息，
也就是work接受的第一个消息就是client_addr，然后work再把处理的响应发给client_addr，
当backend收到消息后，直接通过forentend转发给client_addr，这也是forentend也需要是ROUTER
模式的原因
"""
backend.send(worker_id, zmq.SNDMORE)
backend.send(b"", zmq.SNDMORE)
backend.send(client_addr, zmq.SNDMORE)
backend.send(b"", zmq.SNDMORE)
backend.send(request)
# Out of infinite loop: do some housekeeping
frontend.close()
backend.close()
context.term()
if __name__ == "__main__":
main()
"""
当需要具体转发的时候，就是ROUTER大显身手的时候
"""原文：http://blog.csdn.net/yueguanghaidao/article/details/41814163