TypeError: can't pickle weakref objects when running demo in Simulator mode

[Psychim]

Hi! I tried to run your demo in Simulator mode, but this error occurred after start.
Here is the traceback:

Traceback (most recent call last):  
  File "D:\ProgramData\Anaconda3\lib\site-packages\rtgraph\ui\mainWindow.py", line 62, in start  
    if self.worker.start():  
  File "D:\ProgramData\Anaconda3\lib\site-packages\rtgraph\core\worker.py", line 80, in start  
    self._acquisition_process.start()  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\process.py", line 112, in start  
    self._popen = self._Popen(self)  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 223, in _Popen  
    return _default_context.get_context().Process._Popen(process_obj)  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\context.py", line 322, in _Popen  
    return Popen(process_obj)  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\popen_spawn_win32.py", line 65, in __init__  
    reduction.dump(process_obj, to_child)  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\reduction.py", line 60, in dump  
    ForkingPickler(file, protocol).dump(obj)  
TypeError: can't pickle weakref objects  
Traceback (most recent call last):  
  File "<string>", line 1, in <module>  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 105, in spawn_main  
    exitcode = _main(fd)  
  File "D:\ProgramData\Anaconda3\lib\multiprocessing\spawn.py", line 115, in _main  
    self = reduction.pickle.load(from_parent)  
EOFError: Ran out of input

I found out that this error occurred because self._parser_process.start() is called before self._acquisition_process.start()

And here is my simulated program where the same error occurs:

from multiprocessing import Process,Event
import time
class TestProcess(Process):
    def __init__(self):
        Process.__init__(self)
        self._exit=Event()
    def stop(self):
        self._exit.set()
    def run(self):
        while not self._exit.is_set():
            pass
class TestProcessB(TestProcess):
    def __init__(self,p):
        Process.__init__(self)
        self._test_process=p
    def run(self):
        while not self._exit.is_set():
            print(time.time())
            time.sleep(1)
if __name__=='__main__':
    tp=TestProcess()
    tpb=TestProcessB(tp)
    tp.start()
    tpb.start()
    time.sleep(10)
    tp.stop()
    tpb.stop()

How can this problem be fixed?