Python 线程崩溃

Question

我有一个程序（时间延迟制作器），里面有两个线程在更新一个 wx.StaticBitmap。当这两个线程同时访问这个 wx.StaticBitmap 时，程序就崩溃了，出现了以下错误：

python: xcb_io.c:221: poll_for_event: 断言 `(((long) (event_sequence) - (long) (dpy->request)) <= 0)' 失败。

我尝试过在谷歌搜索这个问题的答案，也试着自己解决，但还是搞不明白。

下面是一段简单的代码，可以重现这个错误 （这不是实际的程序）：

#!/usr/bin/env python

import wx
import time,os.path,glob,threading

class MyFrame(wx.Frame):
    def __init__(self, *args, **kwds):

        kwds["style"] = wx.DEFAULT_FRAME_STYLE
        wx.Frame.__init__(self, *args, **kwds)
        self.bitmap_1 = wx.StaticBitmap(self, -1, wx.NullBitmap)

        self.__set_properties()
        self.__do_layout()

        wx.CallAfter(self._img)
    def __set_properties(self):

        self.SetTitle("frame_1")


    def __do_layout(self):

        sizer_1 = wx.BoxSizer(wx.VERTICAL)
        sizer_1.Add(self.bitmap_1, 0, 0, 0)
        self.SetSizer(sizer_1)
        sizer_1.Fit(self)
        self.Layout()



    def _img(self):
             Thread1= threading.Thread(target=self._img1)
             Thread1.start()
             Thread2 = threading.Thread(target=self._img2)
             Thread2.start()

    def _img1(self):
            frames = glob.glob("/path/to/pngs/*.png")
        frames.sort()
        for i in range(len(frames)):
            if os.path.isfile(frames[i]) and i%2 == 0:
                print frames[i]
                wx.Yield()
                ##time.sleep(0.5)
                wx.CallAfter(self.bitmap_1.SetBitmap,wx.Bitmap(frames[i], wx.BITMAP_TYPE_ANY))
                wx.CallAfter(self.Update)
    def _img2(self):
            frames = glob.glob("/path/to/pngs/*.png")
        frames.sort()
        for i in range(len(frames)):
            if os.path.isfile(frames[i]) and i%2 == 1:
                print frames[i]
                wx.Yield()
                ##time.sleep(0.5)
                wx.CallAfter(self.bitmap_1.SetBitmap,wx.Bitmap(frames[i], wx.BITMAP_TYPE_ANY))
                wx.CallAfter(self.Update)

if __name__ == "__main__":
    app = wx.PySimpleApp(0)
    wx.InitAllImageHandlers()
    frame_1 = MyFrame(None, -1, "")
    app.SetTopWindow(frame_1)
    frame_1.Show()
    app.MainLoop()

我用 wx.PostEvent 解决了这个问题，具体可以看我的回答。

Answer 1

避免程序崩溃和各种异常行为的最简单方法就是确保只有主线程来处理图形用户界面（GUI）。你可以尝试通过找到并锁定关键代码块来做到这一点，但我觉得这样做是没什么效果的。与其这样，不如使用事件来同步处理线程和主线程，这样要简单得多：

while run:
    self.timer_evt.wait()        # wait for main thread to unblock me
    self.timer_evt.clear()
    <process stuff, put results in queue or shared variables>

在处理线程中，

def tick(self):
    if run:
        <update GUI from queued data or shared variables>
        self.timer_evt.set()            # unblock processing thread
        self.root.after(ms, self.tick)  # reschedule the GUI update

在主线程中。

Answer 2

我用 wx.PostEvent 解决了这个问题：

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# generated by wxGlade 0.6.3 on Mon Oct 17 19:59:55 2011

import wx
import time,os.path,glob,threading
# begin wxGlade: extracode
# end wxGlade


ID_START = wx.NewId()
ID_STOP = wx.NewId()

# Define notification event for thread completion
EVT_RESULT_ID = wx.NewId()

def EVT_RESULT(win, func):
    """Define Result Event."""
    win.Connect(-1, -1, EVT_RESULT_ID, func)

class ResultEvent(wx.PyEvent):
    """Simple event to carry arbitrary result data."""
    def __init__(self, data):
        """Init Result Event."""
        wx.PyEvent.__init__(self)
        self.SetEventType(EVT_RESULT_ID)
        self.data = data
class MyFrame(wx.Frame):
    def __init__(self, *args, **kwds):
        # begin wxGlade: MyFrame.__init__
        kwds["style"] = wx.DEFAULT_FRAME_STYLE
        wx.Frame.__init__(self, *args, **kwds)
        self.bitmap_1 = wx.StaticBitmap(self, -1, wx.NullBitmap)
        self.__set_properties()
        self.__do_layout()
        # end wxGlade
    self.frames = ""
    EVT_RESULT(self,self.OnResult)
        wx.CallAfter(self._img)
    def __set_properties(self):
        # begin wxGlade: MyFrame.__set_properties
        self.SetTitle("frame_1")
        # end wxGlade

    def __do_layout(self):
        # begin wxGlade: MyFrame.__do_layout
        sizer_1 = wx.BoxSizer(wx.VERTICAL)
        sizer_1.Add(self.bitmap_1, 0, 0, 0)
        self.SetSizer(sizer_1)
        sizer_1.Fit(self)
        self.Layout()
        # end wxGlade
    def OnResult(self, event):
        """Show Result status."""
        if event.data is None:
            pass
        else:
        self.bitmap_1.SetBitmap(wx.Bitmap(event.data, wx.BITMAP_TYPE_ANY))
# end of class MyFrame
    def _img(self):
             Thread1= threading.Thread(target=self._img1)
             Thread1.start()
             Thread2 = threading.Thread(target=self._img2)
             Thread2.start()

    def _img1(self):
            frames = glob.glob("/home/mitch/Pictures/*.png")
        frames.sort()

        for i in range(len(frames)):
            if os.path.isfile(frames[i]) and i%2 == 0:
                print frames[i]
                ##wx.Yield()
                ##time.sleep(0.5)
                wx.PostEvent(self, ResultEvent(frames[i]))

    def _img2(self):
            frames = glob.glob("/home/mitch/Pictures/*.png")
        frames.sort()

        for i in range(len(frames)):
            if os.path.isfile(frames[i]) and i%2 == 1:
                print frames[i]
                ##wx.Yield()
                ##time.sleep(0.5)
                wx.PostEvent(self, ResultEvent(frames[i]))

if __name__ == "__main__":
    app = wx.PySimpleApp(0)
    wx.InitAllImageHandlers()
    frame_1 = MyFrame(None, -1, "")
    app.SetTopWindow(frame_1)
    frame_1.Show()
    app.MainLoop()