Cannot start multiprocessing when file compiled using Pyinstaller

This is the imported lib in my code

from tkinter import *
from BacaRupa import main_detect, check_temp
from multiprocessing import Value
from ctypes import Structure, c_double
from PIL import Image, ImageTk
from Logo import *
import tkinter.font as tkFont
import os
import sys
import serial.tools.list_ports
import multiprocessing

I'm using this code to run multiprocessing.

try:
    # Python 3.4+
    if sys.platform.startswith('win'):
        import multiprocessing.popen_spawn_win32 as forking
    else:
        import multiprocessing.popen_fork as forking
except ImportError:
    import multiprocessing.forking as forking

if sys.platform.startswith('win'):
    class _Popen(forking.Popen):
        def __init__(self, *args, **kw):
            if hasattr(sys, 'frozen'):
                # We have to set original _MEIPASS2 value from sys._MEIPASS
                # to get --onefile mode working.
                os.putenv('_MEIPASS2', sys._MEIPASS)
            try:
                super(_Popen, self).__init__(*args, **kw)
            finally:
                if hasattr(sys, 'frozen'):
                    # On some platforms (e.g. AIX) 'os.unsetenv()' is not
                    # available. In those cases we cannot delete the variable
                    # but only set it to the empty string. The bootloader
                    # can handle this case.
                    if hasattr(os, 'unsetenv'):
                        os.unsetenv('_MEIPASS2')
                    else:
                        os.putenv('_MEIPASS2', '')

    # Second override 'Popen' class with our modified version.
    forking.Popen = _Popen

class Process(multiprocessing.Process):
    _Popen = _Popen

This function get called by if name == 'main':

def PanggilBacaRupa():
    import time
    y = Value(c_double, 0)
    is_stop = Value('i',0)
    multiprocessing.freeze_support()
    p = Process(target=check_temp, args=(y,is_stop))
    p.start()
    
    if entrySuhu.get() == "":
        main_detect(y, is_stop, 0)
    else:
        main_detect(y, is_stop, entrySuhu.get())

When runned using python this program run successfully, but when compiled to .exe this program can't do multiprocessing. What should i do? i compiled with pyinstaller GUI.spec --windowed --onefile.