使用KivyMD+多进程启动双窗口时出现XIO致命错误求助

Root Cause #

The error stems from Linux's default fork multiprocessing start method, which inherits the parent process's X11 display connection. X11 doesn’t allow multiple processes to share the same connection, leading to sequence number conflicts and fatal IO errors.

Step-by-Step Fix #

1. Use the spawn start method: This initializes each child process from scratch instead of inheriting the parent’s resources (including the X connection), eliminating conflicts.
2. Run independent Kivy/KivyMD Apps per process: Each process must create its own instance of an App subclass—never share widgets or app instances across processes.
3. Isolate process UI contexts: Ensure each child process manages its own UI entirely, with no cross-process UI object sharing.

Corrected Pure Kivy Example #

import multiprocessing
from kivy.app import App
from kivy.uix.label import Label

def launch_window(window_title):
    class WindowApp(App):
        def build(self):
            self.title = window_title
            return Label(text=f"Window: {window_title}", font_size=24)
    
    WindowApp().run()

if __name__ == '__main__':
    # Switch to spawn start method to avoid X connection inheritance
    multiprocessing.set_start_method('spawn')
    
    # Launch two separate windows
    proc1 = multiprocessing.Process(target=launch_window, args=("First Window",))
    proc2 = multiprocessing.Process(target=launch_window, args=("Second Window",))
    
    proc1.start()
    proc2.start()
    
    proc1.join()
    proc2.join()

KivyMD Adaptation #

The same logic applies to KivyMD—each process runs its own independent MDApp instance:

import multiprocessing
from kivymd.app import MDApp
from kivymd.uix.label import MDLabel

def launch_md_window(window_title):
    class MDWindowApp(MDApp):
        def build(self):
            self.title = window_title
            return MDLabel(text=f"KivyMD Window: {window_title}", halign="center", font_size=24)
    
    MDWindowApp().run()

if __name__ == '__main__':
    multiprocessing.set_start_method('spawn')
    
    proc1 = multiprocessing.Process(target=launch_md_window, args=("MD Window 1",))
    proc2 = multiprocessing.Process(target=launch_md_window, args=("MD Window 2",))
    
    proc1.start()
    proc2.start()
    
    proc1.join()
    proc2.join()

Key Notes #

• No cross-process UI sharing: Kivy/KivyMD UI objects are not designed to be shared between processes—each process must handle its own UI lifecycle.
• spawn overhead: This method has minor overhead compared to fork, but it’s mandatory for UI-related multiprocessing in Kivy on Linux.
• DISPLAY variable: The spawn method inherits the parent’s environment, so your DISPLAY setting (usually :0) will work automatically.

内容的提问来源于stack exchange，提问作者George Răbuș