Async callback with custom object causes invalid reference counting handling

[Rico Hauke]

Hi All,

the following code makes RPyC 3.3.0 crash on my machine because of too early reference counting decrease.

Please note the following conditions:

- Synchronous client call that passes a callback function to the server.

- Asynchronous callback (event) that calls the received callback function.

- The event passes an object back to the client whose class definition is unknown on the client side.

After debugging the code and tracing the protocol, it seems that the callback function is requested to be deleted from the local objects dictionary on the client side,

before the callback on this function is actually executed. And the callback call is actually delayed because the parameter class definition is unknown on the client side.

Unfortunately, I haven't figured out where to fix the error.

I would assume that the delete request needs to be delayed until the callback finished. Note that the callback is asynchronous.

Thanks for any help,

Rico

Server code:

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

import rpyc

import os

class URL (str):

    pass

class DownloadService (rpyc.Service):

    def exposed_download_url (self, url, finished):

        a = rpyc.async(finished)

        a(URL(url))

if __name__ == '__main__':

    print os.getpid()

    from rpyc.utils.server import ThreadedServer

    serv = ThreadedServer(DownloadService, port=18812, protocol_config={"allow_all_attrs": True})

    serv.start()

Client code:

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

import logging

import rpyc

def finished (self, url):

    print "Finished."

if __name__ == '__main__':

    url = "http://www.car-it.com/wp-content/uploads/2014/02/13C1150_092.jpg"

    logging.basicConfig(level=logging.DEBUG)

    log = logging.getLogger(__name__)

    con = rpyc.connect("localhost", port=18812, config={"allow_all_attrs": True, "logger": log})

    con.root.download_url(url, finished)

    

    # Keep alive.

    while True:

        pass

Client side exception:

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

pydev debugger: starting (pid: 1988)

DEBUG:__main__:Exception caught

Traceback (most recent call last):

  File "C:\Program Files (x86)\Python27\lib\site-packages\rpyc\core\protocol.py", line 305, in _dispatch_request

    res = self._HANDLERS[handler](self, *args)

  File "C:\Program Files (x86)\Python27\lib\site-packages\rpyc\core\protocol.py", line 535, in _handle_call

    return self._local_objects[oid](*args, **dict(kwargs))

  File "C:\Program Files (x86)\Python27\lib\site-packages\rpyc\lib\colls.py", line 86, in __getitem__

    return self._dict[key][0]

KeyError: 40805104

Protocol trace (seq, msg):

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Client:                                                                         Server:

-------                                                                           -------

--> REQ                                                                        (0, 1): GetRoot()

(0, 2): (41243912, 'DownloadService', 'pkgs.dlserv')           <-- RESP

--> REQ                                                                        (1, 1): Inspect(41243912)

(1, 2): <List of methods>                                                <-- RESP

--> REQ                                                                        (2, 1): GetAttr(41243912, 'download_url')

(2, 2): (38883696, 'instancemethod', '__builtin__')              <-- RESP

--> REQ                                                                        (3, 1): Call(38883696, url, finished=(40805104, 'function', '__builtin__'))

(0, 1): Call(40805104, url=(41284640, 'URL', '__main__'))    <-- REQ

(3, 2): None                                                                    <-- RESP

(1, 1): Del(40805104)                                                       <-- REQ

--> REQ                                                                         (4, 1): Inspect(41284640)

(4, 2): <Class description>                                               <-- RESP

--> RESP                                                                       (1, 2): None

--> EXCP                                                                       (0, 3): KeyError(40805104)