python - set is being modified and then seems to magically revert -


i'm trying build channel reliable delivery on top of unreliable channel (it's exercise, unreliable channel explicitly drops of packets). have acks set contains (address, sequence_number) pairs. when ack received on channel it's added acks set , condition variable notified:

msg, addr = self.unreliable_channel.recv() if isinstance(msg, ack):     self.acks_cond:         self.acks.add((addr, msg.ack))         print "{} got ack: {} ({})".format(self.port, self.acks, hex(id(self.acks)))         self.acks_cond.notify()

a different thread listening on condition variable , checking acks in thread:

with self.acks_cond:     max_wait = 2 * self.unreliable_channel.delay_avg     start = time.time()     while not ((addr, msg.seq) in self.acks) , (time.time() - start < max_wait):         print "{}: self.acks {} ({})".format(self.port, self.acks, hex(id(self.acks)))         self.acks_cond.wait(0.1)     print "{} waited ack of {} {}: {} ({})".format(self.port, msg.seq, addr, self.acks, hex(id(self.acks)))     if (addr, msg.seq) in self.acks:         print '!' * 10000         # self.acks.remove((addr, msg.seq))         return

however, second snippet can't seem see modified set:

10000 got ack: set([(('192.168.1.7', 10001), 1), 'toplel']) (0x7f40a944ced0) 10000: self.acks set(['toplel']) (0x7f40a944ced0)

('toplel' string threw in set make sure wasn't somehow being emptied)

anyone have idea of messing up?

code dump below: (tried making sscce couldn't seem reproduce behavior -- i'll try more though if one).

import threading import time collections import defaultdict, namedtuple  message = namedtuple('message', ['seq', 'data']) ack = namedtuple('ack', ['ack'])  class reliablechannel:     '''building on top of unreliablechannel, channel supports     guarenteed eventual delivery, fifo delivery on per-destination     basis, , no duplicated delivery.'''      def __init__(self, unreliable_channel):         self.unreliable_channel = unreliable_channel          # set of (addr, seq) pairs we've recieved acks         print "initializing toplel"         self.acks = set(["toplel"])         self.acks_cond = threading.condition()          self.seq = defaultdict(int)          self.port = self.unreliable_channel.sock.getsockname()[1]         print 'self.port: {}'.format(self.port)          # leftoff: thread started can't seem modify self.acks unicast can see         self.listener = threading.thread(target=self.listen)         self.listener.start()      def listen(self):         while true:             msg, addr = self.unreliable_channel.recv()             if isinstance(msg, ack):                 self.acks_cond:                     self.acks.add((addr, msg.ack))                     print "{} got ack: {} ({})".format(self.port, self.acks, hex(id(self.acks)))                     self.acks_cond.notify()             else:                 ack = ack(msg.seq)                 self.unreliable_channel.unicast(ack, addr)                 print '{} got message {} , sent {} {}'.format(self.port, msg, ack, addr)      def unicast(self, msg, addr):         self.seq[addr] += 1  # sequence number message         msg = message(self.seq[addr], msg)         print '{} trying send message {} {}'.format(self.port, msg, addr)         while true:             # send message             self.unreliable_channel.unicast(msg, addr)              # wait ack timeout             self.acks_cond:                 max_wait = 2 * self.unreliable_channel.delay_avg                 start = time.time()                 while not ((addr, msg.seq) in self.acks) , (time.time() - start < max_wait):                     print "{}: self.acks {} ({})".format(self.port, self.acks, hex(id(self.acks)))                     self.acks_cond.wait(0.1)                 print "{} waited ack of {} {}: {} ({})".format(self.port, msg.seq, addr, self.acks, hex(id(self.acks)))                 if (addr, msg.seq) in self.acks:                     print '!' * 10000                     # self.acks.remove((addr, msg.seq))                     return

edit: after doing more messing around, seems sets "diverge" in 2 threads after while. depending on in listen, modifications list take, after that, seems each thread working own copy of set (ie, tried adding stuff set in both threads).

self-answer: knew stupid. __init__ method above launches thread, , being run in __init__ method of multiprocessing.process subclass. meaning thread running listen being launched in 1 process, while thread running unicast being run in separate one, dup-ed copy of set guess.

should've realized sooner fact ids same throwing me off -- guess figured forked process own virtual addresses, odds of being same 1 low. didn't think assume re-use same virtual address.

tl;dr: id(x) == id(y) doesn't mean x , y same object if you're messing multiprocessing.


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