Websocket call-and-response

# how to await call-and-response over a websocket
# assuming the remote server preserves the message ID

from threading import Thread, Event
import queue
from time import sleep

# websocket simulator

ws_in = queue.Queue()
ws_out = queue.Queue()

# server simulator

def pubsub():   # server publishes data; I subscribe
    for n in range(8):
        sleep(1)
        ws_in.put({'type': 'notif', 'data': n+101})
def rpc():      # I call procedure on server; server replies
    def put(id):
        sleep(3)
        ws_in.put({'type': 'reply', 'id': id, 'data': id+10})
    while True:
        Thread(target=put, args=[ws_out.get()]).start()
Thread(target=pubsub).start()
Thread(target=rpc).start()

# me

awaiting = {}

def ws_receiver():
    while True:
        on_message(ws_in.get())

def on_message(msg):    # ws callback
    if msg['type'] == 'reply':      # handle rpc like this
        awaiting[msg['id']]['reply'] = msg['data']  # first writes reply
        awaiting[msg['id']]['received'].set()       # then signals that reply is set
    elif msg['type'] == 'notif':    # handle pubsub as usual
        print(msg['data'])

def send(id):           # called by whatever wants to send something
    received = Event()                      # a sync primitive like Lock
    awaiting[id] = {'received': received}   # init state of rpc; 'reply' field to be set
    ws_out.put(id)                          # sends rpc
    print('ws send %s' % (id))              # awaiting[id] set by ws callback
    if received.wait(5):                    # await received event to be set
        reply = awaiting.pop(id)['reply']   # get reply
        print('ws receive %s: %s' % (id, reply))
        return reply                        # back to caller
    else:                                   # timeout
        print('ws timeout on %s' % (id))

Thread(target=ws_receiver).start()

# test

sleep(2.7)
Thread(target=send, args=[3]).start()
sleep(0.5)
Thread(target=send, args=[4]).start()