无法在 Windows 的多处理环境中“腌制”Tkinter 对象

Question

我正在尝试创建一个应用程序，其中 Tkinter GUI 由其他不断获取数据的对象更新。我在使用多线程时遇到了问题，所以我决定尝试使用多处理模块。

我发现您无法在 multiprocessing.Process 内运行 Tkinter 窗口，这是最小的示例：

import Tkinter as tk
import multiprocessing

class Subprocess(multiprocessing.Process):
    def __init__(self):
        multiprocessing.Process.__init__(self)
        self.root = tk.Tk()
    #

    def run(self):
        self.root.mainloop()
    #

    def stop(self):
        self.root.destroy()
        self.terminate()


if __name__ == '__main__':
        process = Subprocess()
        process.start()
        print "I got around the global interpreter lock"
        raw_input()
        print "exiting"
        process.stop()

我期望发生的是弹出一个 Tk 窗口，并且“我绕过了全局解释器锁定”显示在终端中。我在 ubuntu linux 上对此进行了测试，它运行良好，但是当我切换到 Windows 7（我正在开发我的应用程序）时，它没有给我错误：

Traceback (most recent call last):
  File "C:\pathtoscript\multiprocessing_test.py", line 21, in <module>
    process.start()
  File "C:\Python27\lib\multiprocessing\process.py", line 130, in start
    self._popen = Popen(self)
  File "C:\Python27\lib\multiprocessing\forking.py", line 277, in __init__
    dump(process_obj, to_child, HIGHEST_PROTOCOL)
  File "C:\Python27\lib\multiprocessing\forking.py", line 199, in dump
    ForkingPickler(file, protocol).dump(obj)
  File "C:\Python27\lib\pickle.py", line 224, in dump
    self.save(obj)
  File "C:\Python27\lib\pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "C:\Python27\lib\pickle.py", line 419, in save_reduce
    save(state)
  File "C:\Python27\lib\pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "C:\Python27\lib\pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "C:\Python27\lib\pickle.py", line 681, in _batch_setitems
    save(v)
  File "C:\Python27\lib\pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "C:\Python27\lib\pickle.py", line 725, in save_inst
    save(stuff)
  File "C:\Python27\lib\pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "C:\Python27\lib\pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "C:\Python27\lib\pickle.py", line 681, in _batch_setitems
    save(v)
  File "C:\Python27\lib\pickle.py", line 313, in save
    (t.__name__, obj))
PicklingError: Can't pickle 'tkapp' object: <tkapp object at 0x02BD3D08>

有人知道解决方法吗？这对我来说似乎很奇怪，这适用于 linux 但不适用于 Windows。

Answer 1

这是一个简单的修复 - 只需在子进程而不是父进程中创建 tkapp 对象：

import Tkinter as tk
import multiprocessing
from Queue import Empty

class Subprocess(multiprocessing.Process):
    def __init__(self):
        multiprocessing.Process.__init__(self)
        self.queue = multiprocessing.Queue()
    #

    def run(self):
        self.root = tk.Tk()
        self.root.after(100, self._check_queue) # Check the queue every 100ms
        self.root.mainloop()

    def _check_queue(self):
        try:
            out = self.queue.get_nowait()
            if out == 'stop':
                self.do_stop()
                return
            # Could check for other commands here, too
        except Empty:
            pass
        self.root.after(100, self._check_queue)

    def stop(self):
        self.queue.put('stop')

    def do_stop(self):
        self.root.destroy()


if __name__ == '__main__':
    process = Subprocess()
    process.start()
    print "I got around the global interpreter lock"
    raw_input()
    print "exiting"
    process.stop()

尝试在父级中创建tkapp，然后在子级中开始，这不是一个可行的解决方案。唯一棘手的部分是您需要使用Queue 来告诉子进程中的循环从父进程中停止。

另外，无论如何，在 Linux 上运行原始代码实际上会导致解释器崩溃：

XIO:  fatal IO error 11 (Resource temporarily unavailable) on X server ":0"
      after 87 requests (87 known processed) with 0 events remaining.
[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
python: ../../src/xcb_io.c:274: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.