For some reason this python multiprocessing code is not working-CodePudding

So, I am just starting out with Python multiprocessing. I tried this example but didn't get it to quite work:

import multiprocessing

def function():
    time.sleep(1)
    print("slept once")

p1 = multiprocessing.Process(target=function)
p2 = multiprocessing.Process(target=function)

p1.start()
p2.start()

it should output this:

(sleeping 1 second)
slept once
slept once

but instead it gave me an error:

Traceback (most recent call last):
 File "<string>", line 1, in <module>
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_main
   exitcode = _main(fd)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 114, in _main
   prepare(preparation_data)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 225, in prepare
   _fixup_main_from_path(data['init_main_from_path'])
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
   run_name="__mp_main__")
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 263, in run_path
   pkg_name=pkg_name, script_name=fname)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 96, in _run_module_code
   mod_name, mod_spec, pkg_name, script_name)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 85, in _run_code
   exec(code, run_globals)
 File "C:\Users\krist\PycharmProjects\chat_app\client_1.py", line 11, in <module>
   p1.start()
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\process.py", line 105, in start
   self._popen = self._Popen(self)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 223, in _Popen
   return _default_context.get_context().Process._Popen(process_obj)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 322, in _Popen
   return Popen(process_obj)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
   prep_data = spawn.get_preparation_data(process_obj._name)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
   _check_not_importing_main()
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\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.
Traceback (most recent call last):
 File "<string>", line 1, in <module>
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 105, in spawn_main
   exitcode = _main(fd)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 114, in _main
   prepare(preparation_data)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 225, in prepare
   _fixup_main_from_path(data['init_main_from_path'])
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 277, in _fixup_main_from_path
   run_name="__mp_main__")
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 263, in run_path
   pkg_name=pkg_name, script_name=fname)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 96, in _run_module_code
   mod_name, mod_spec, pkg_name, script_name)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\runpy.py", line 85, in _run_code
   exec(code, run_globals)
 File "C:\Users\krist\PycharmProjects\chat_app\client_1.py", line 11, in <module>
   p1.start()
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\process.py", line 105, in start
   self._popen = self._Popen(self)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 223, in _Popen
   return _default_context.get_context().Process._Popen(process_obj)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\context.py", line 322, in _Popen
   return Popen(process_obj)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\popen_spawn_win32.py", line 33, in __init__
   prep_data = spawn.get_preparation_data(process_obj._name)
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\lib\multiprocessing\spawn.py", line 143, in get_preparation_data
   _check_not_importing_main()
 File "C:\Users\krist\AppData\Local\Programs\Python\Python36\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.

I am using windows 11, python 3.6

Hope someone can help!

Here is just a bunch of random stuff because stackoverflow would not allow me to post this otherwise:

data:1,myfile;1:0_sub_.error:help.error:help.data:1,myfile;1:0_sub_ error:help.data:1,myfile;1:0_sub_error:help.data:1,myfile;1:0_sub_error:help.data:1,myfile;1:0_sub_ ;;rm.0000;ip/ip.error:help.data:1,myfile;1:0_sub_

CodePudding user response：

Your code works fine if you add in the expected idiom:

import time
import multiprocessing

def function():
    time.sleep(1)
    print("slept once")

if __name__ == '__main__':
   p1 = multiprocessing.Process(target=function)
   p2 = multiprocessing.Process(target=function)

   p1.start()
   p2.start()

CodePudding user response：

You can't start a new process unless you follow the multiprocessing library's guidelines[1].

There is a specific guideline in this library how the start() method should only be running within the if __name__ == '__main__ conditional.

Why? Because it's safer to spawn new processes while the files running directly and not being imported.

So, this should do the trick:

import multiprocessing
import time


def function():
    time.sleep(1)
    print("slept once")

p1 = multiprocessing.Process(target=function)
p2 = multiprocessing.Process(target=function)

if __name__ == '__main__':
    p1.start()
    p2.start()

[0]How to use the MultiProcessing library? https://docs.python.org/3/library/multiprocessing.html

[1]https://docs.python.org/3/library/multiprocessing.html#multiprocessing-programming