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import Queue, threading
should_exit = False
class DummyReply:
"""
A reply object that does nothing. Useful when we need an object to seem
like it has a channel, and during testing.
"""
def __init__(self):
self.acked = False
def __call__(self, msg=False):
self.acked = True
class Reply:
"""
Messages sent through a channel are decorated with a "reply" attribute.
This object is used to respond to the message through the return
channel.
"""
def __init__(self, obj):
self.obj = obj
self.q = Queue.Queue()
self.acked = False
def __call__(self, msg=None):
if not self.acked:
self.acked = True
if msg is None:
self.q.put(self.obj)
else:
self.q.put(msg)
class Channel:
def __init__(self, q):
self.q = q
def ask(self, mtype, m):
"""
Decorate a message with a reply attribute, and send it to the
master. then wait for a response.
"""
m.reply = Reply(m)
self.q.put((mtype, m))
while not should_exit:
try:
# The timeout is here so we can handle a should_exit event.
g = m.reply.q.get(timeout=0.5)
except Queue.Empty: # pragma: nocover
continue
return g
def tell(self, mtype, m):
"""
Decorate a message with a dummy reply attribute, send it to the
master, then return immediately.
"""
m.reply = DummyReply()
self.q.put((mtype, m))
class Slave(threading.Thread):
"""
Slaves get a channel end-point through which they can send messages to
the master.
"""
def __init__(self, channel, server):
self.channel, self.server = channel, server
self.server.set_channel(channel)
threading.Thread.__init__(self)
def run(self):
self.server.serve_forever()
class Master:
"""
Masters get and respond to messages from slaves.
"""
def __init__(self, server):
"""
server may be None if no server is needed.
"""
self.server = server
self.masterq = Queue.Queue()
def tick(self, q):
changed = False
try:
# This endless loop runs until the 'Queue.Empty'
# exception is thrown. If more than one request is in
# the queue, this speeds up every request by 0.1 seconds,
# because get_input(..) function is not blocking.
while True:
# Small timeout to prevent pegging the CPU
msg = q.get(timeout=0.01)
self.handle(*msg)
changed = True
except Queue.Empty:
pass
return changed
def run(self):
global should_exit
should_exit = False
self.server.start_slave(Slave, Channel(self.masterq))
while not should_exit:
self.tick(self.masterq)
self.shutdown()
def handle(self, mtype, obj):
c = "handle_" + mtype
m = getattr(self, c, None)
if m:
m(obj)
else:
obj.reply()
def shutdown(self):
global should_exit
if not should_exit:
should_exit = True
if self.server:
self.server.shutdown()
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