New submission from Tim Peters <t...@python.org>:
This started on StackOverflow: https://stackoverflow.com/questions/63623651/how-to-properly-share-manager-dict-between-processes Here's a simpler program. Short course: an object of a subclass of mp.Process has an attribute of seemingly any type obtained from an mp.Manager(). The report above used a Manager.dict, and the program here a Manager.Value. When .start() is invoked, the first time that attribute is used in any way that requires communication with the Manager server, the program dies. The output below is from 3.8.5 on Windows; the report above is some Linux flavor. The tracebacks are very similar, the only obvious difference being that the implementation complains about a socket on Linux but about a named pipe on Windows. Note that there's no problem passing such things as explicit arguments to functions across processes. The loss here appears specific to the inscrutable under-the-covers pickle dance needed to create a "self" by magic on worker processes. The code: from multiprocessing import Process, Manager, Event class MyProducer(Process): def __init__(self, value, event): Process.__init__(self) self.val = value self.event = event def run(self): print("at producer start:", self.val.value) self.val.value = 42 self.event.set() class MyConsumer(Process): def __init__(self, value, event): Process.__init__(self) self.val = value self.event = event def run(self): self.event.wait() print("in consumer:", self.val.value) if __name__ == "__main__": state_value = Manager().Value('i', 666) print("at start:", state_value.value) state_ready = Event() producerprocess = MyProducer(state_value, state_ready) consumerprocess = MyConsumer(state_value, state_ready) producerprocess.start() consumerprocess.start() The output: at start: 666 Process MyProducer-2: Traceback (most recent call last): File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\managers.py", line 827, in _callmethod conn = self._tls.connection AttributeError: 'ForkAwareLocal' object has no attribute 'connection' During handling of the above exception, another exception occurred: Traceback (most recent call last): File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\process.py", line 315, in _bootstrap self.run() File "C:\Code\temp.py", line 10, in run print("at producer start:", self.val.value) File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\managers.py", line 1154, in get return self._callmethod('get') File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\managers.py", line 831, in _callmethod self._connect() File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\managers.py", line 818, in _connect conn = self._Client(self._token.address, authkey=self._authkey) File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\connection.py", line 500, in Client c = PipeClient(address) File "C:\Users\Tim\AppData\Local\Programs\Python\Python38\lib\multiprocessing\connection.py", line 702, in PipeClient _winapi.WaitNamedPipe(address, 1000) FileNotFoundError: [WinError 2] The system cannot find the file specified ---------- components: Library (Lib) messages: 376051 nosy: tim.peters priority: normal severity: normal status: open title: multiprocessing.Manager objects lose connection info type: behavior versions: Python 3.8 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue41660> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
