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   在進行python3多程序multiprocessing學習過程中，在Windows環境下測試分散式程式碼過程中，利用fork()生成child processes的程式碼須放在main模組中，否則將會報錯：

程式碼如下：

import queue
import random
from multiprocessing.managers import BaseManager

task_queue = queue.Queue()
result_queue = queue.Queue()

def return_task_queue():
    global task_queue
    return task_queue

def return_result_queue():
    global result_queue
    return result_queue

class QueueManager(BaseManager):
    pass


QueueManager.register('get_task_queue', callable=return_task_queue)
QueueManager.register('get_result_queue', callable=return_result_queue)

manager = QueueManager(address=('127.0.0.1', 5000), authkey=b'abc')
manager.start()

task = manager.get_task_queue()
result = manager.get_result_queue()
for i in range(10):
    n = random.randint(0, 10000)
    print('Put task %d' % n)
    task.put(n)

print('Try get results..')
for i in range(10):
    r = result.get(timeout=10)
    print('Result:%s' % r)

manager.shutdown()
print('master exit.')
 

"E:\python\python project\myfirst\venv\Scripts\python.exe" "E:/python/python project/myfirst/vari/distibuted_master.py"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 105, in spawn_main
    exitcode = _main(fd)
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 114, in _main
    prepare(preparation_data)
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 225, in prepare
    _fixup_main_from_path(data['init_main_from_path'])
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
    run_name="__mp_main__")
  File "D:\program files\Python3.6\Lib\runpy.py", line 263, in run_path
    pkg_name=pkg_name, script_name=fname)
  File "D:\program files\Python3.6\Lib\runpy.py", line 96, in _run_module_code
    mod_name, mod_spec, pkg_name, script_name)
  File "D:\program files\Python3.6\Lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "E:\python\python project\myfirst\vari\distibuted_master.py", line 24, in <module>
    manager.start()
  File "D:\program files\Python3.6\Lib\multiprocessing\managers.py", line 513, in start
    self._process.start()
  File "D:\program files\Python3.6\Lib\multiprocessing\process.py", line 105, in start
    self._popen = self._Popen(self)
  File "D:\program files\Python3.6\Lib\multiprocessing\context.py", line 322, in _Popen
    return Popen(process_obj)
  File "D:\program files\Python3.6\Lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
    prep_data = spawn.get_preparation_data(process_obj._name)
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 143, in get_preparation_data
    _check_not_importing_main()
  File "D:\program files\Python3.6\Lib\multiprocessing\spawn.py", line 136, in _check_not_importing_main
    is not going to be frozen to produce an executable.''')
RuntimeError: 
        An attempt has been made to start a new process before the
        current process has finished its bootstrapping phase.

        This probably means that you are not using fork to start your
        child processes and you have forgotten to use the proper idiom
        in the main module:

            if __name__ == '__main__':
                freeze_support()
                ...

        The "freeze_support()" line can be omitted if the program
        is not going to be frozen to produce an executable.

Process finished with exit code 1
 

import queue
import random
from multiprocessing.managers import BaseManager

task_queue = queue.Queue()
result_queue = queue.Queue()

def return_task_queue():
    global task_queue
    return task_queue

def return_result_queue():
    global result_queue
    return result_queue

class QueueManager(BaseManager):
    pass

if __name__=='__main__':
    QueueManager.register('get_task_queue', callable=return_task_queue)
    QueueManager.register('get_result_queue', callable=return_result_queue)

    manager = QueueManager(address=('127.0.0.1', 5000), authkey=b'abc')
    manager.start()

    task = manager.get_task_queue()
    result = manager.get_result_queue()
    for i in range(10):
        n = random.randint(0, 10000)
        print('Put task %d' % n)
        task.put(n)

    print('Try get results..')
    for i in range(10):
        r = result.get(timeout=10)
        print('Result:%s' % r)

    manager.shutdown()
    print('master exit.')
 

"E:\python\python project\myfirst\venv\Scripts\python.exe" "E:/python/python project/myfirst/vari/distibuted_master.py"
Put task 5292
Put task 5986
Put task 3500
Put task 2385
Put task 8343
Put task 6482
Put task 4331
Put task 6104
Put task 9341
Put task 5156
Try get results..

Process finished with exit code 1

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