间歇性Python线程错误，“主线程不在主循环中" [英] Intermittent Python thread error, "main thread is not in main loop"

问题描述

中年爸爸(电气工程师不是程序员)试图教我 13 岁的女儿电子学和编程.到目前为止，我喜欢 Python.我正在构建一个程序，使用 tkinter GUI 和 DS18B20 传感器显示整个房子的温度.

Middle aged dad (electrical engineer not programmer by trade) trying to teach my 13 year old daughter electronics and programming. So far, I love Python. I am building a program to display temperatures throughout our house with tkinter GUI and DS18B20 sensors.

我们通过阅读书籍、在线研究和使用 Stack Overflow 来解决错误(这个网站太棒了！)拼凑了下面的程序.

We've pieced together the program below from reading books, online research and using Stack Overflow for trouble-shooting bugs (this site rocks!).

现在我们被难住了，我们不断收到间歇性错误，当我们在 Raspberry 上加载空闲后第一次运行程序时，它工作正常.

Now we're stumped, we keep getting an intermittent error, when we run the program the first time after loading idle on our Raspberry, it works fine.

第二次，以及随后的所有时间，我们都会收到此错误消息:

The second time, and all subsequent times, we get this error message:

Traceback (most recent call last):
  File "/home/pi/Code-working-library/stackoverflow-paste.py", line 140, in <module>
    app.equipTemp.set(tempread)
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 203, in set
    return self._tk.globalsetvar(self._name, value)
RuntimeError: main thread is not in main loop

注意，我们的理解是，为了有一个静态窗口和更新标签，我们需要使用一个线程来读取我们的传感器 (DS18B20) 的更新温度.我们开始的示例代码有 _init_ 语句，前面和后面只有一个下划线 - 不知道为什么，如果我添加第二个下划线，我会收到错误消息.我们用作基础的更新窗口代码来自树莓派论坛

Note, our understanding is that in order to have a static window and update labels updated temps read off our sensor (DS18B20) we needed to use a thread. The sample code we started with has the _init_ statements with only one underscore preceding and trailing - not sure why, if I add a second underscore, I get error messages. The updating window code we used as our basis came from Raspberry Pi forum

这是我们的代码:

from Tkinter import *
import tkFont
import os
import glob
import time
import subprocess
import re
import sys
import time
import threading
import Image 
import ImageTk

os.system('modprobe w1-gpio')
os.system('modprobe w1-therm')

#28-000005c6ba08

sensors = ['28-000005c6ba08'] 
sensors1 = ['28-000005c70f69'] 

def read_temp_raw():
    catdata = subprocess.Popen(['cat',device_file], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    out,err = catdata.communicate()
    out_decode = out.decode('utf-8')
    lines = out_decode.split('\n')
    return lines

def read_temp():
    lines = read_temp_raw()
    while lines[0].strip()[-3:] != 'YES':
        time.sleep(0.2)
        lines = read_temp_raw()
    equals_pos = lines[1].find('t=')
    if equals_pos != -1:
        temp_string = lines[1][equals_pos+2:]
        temp_c = float(temp_string) / 1000.0
        temp_f = temp_c * 9.0 / 5.0 + 32.0
        return temp_f

###########  build window  ###################

bground="grey"


class App(threading.Thread):

    def _init_(self):    
        threading.Thread._init_(self)
        self.start()

    def callback(self):
        self.root.quit()        


    def run(self):

        #Make the window
        self.root = Tk() 
        self.root.wm_title("Home Management System")
        self.root.minsize(1440,1000)

        self.equipTemp = StringVar()   
        self.equipTemp1 = StringVar()
        self.equipTemp2 = StringVar()       

        self.customFont = tkFont.Font(family="Helvetica", size=16)

        #   1st floor Image
        img = Image.open("HOUSE-PLANS-01.png") 
        photo = ImageTk.PhotoImage(img)

        Label1=Label(self.root, image=photo)
        Label1.place(x=100, y=100)

        #   2nd floor
        img2 = Image.open("HOUSE-PLANS-02.png")
        photo2 = ImageTk.PhotoImage(img2)

        Label1=Label(self.root, image=photo2)
        Label1.place(x=600, y=100)

        #   Basement image
        img3 = Image.open("HOUSE-PLANS-03.png")
        photo3 = ImageTk.PhotoImage(img3)

        Label1=Label(self.root, image=photo3)
        Label1.place(x=100, y=500)

        #   Attic Image
        img4 = Image.open("HOUSE-PLANS-04.png")
        photo4 = ImageTk.PhotoImage(img4)

        Label1=Label(self.root, image=photo4)
        Label1.place(x=600, y=500)

        #   House Isometric Image
        img5 = Image.open("house-iso.png")
        photo5 = ImageTk.PhotoImage(img5)

        Label1=Label(self.root, image=photo5)
        Label1.place(x=1080, y=130)

        #Garage Temp Label
        Label2=Label(self.root, textvariable=self.equipTemp, width=6, justify=RIGHT, font=self.customFont)
        Label2.place(x=315, y=265)



        print "start monitoring and updating the GUI"

        self.root.mainloop() #start monitoring and updating the GUI



###########  Start Loop    ###################

print "starting app"

app = App()
app.start()

print "app started"


###################  Begin ds18b20 function  ##############

while True:

    #   28-000005c6ba08
    i = "28-000005c6ba08"
    base_dir = '/sys/bus/w1/devices/'
    device_folder = glob.glob(base_dir + i)[0]
    device_file = device_folder + '/w1_slave'

    tempread=round(read_temp(),1)


    app.equipTemp.set(tempread)
    time.sleep(5)

    ##################### END ds18b20 Function  ######

推荐答案

GUI代码需要在主线程运行，测温代码需要在后台线程运行.只有在主线程中更新 GUI 才是安全的，因此您可以将您从后台线程读取的温度数据通过 Queue 传递回主线程，并让主线程定期检查使用 self.root.after() 获取队列中的数据:

You need to run the GUI code in the main thread, and your temperature reading code needs to be in the background thread. It's only safe to update the GUI in the main thread, so you can pass the temperature data you're reading from the background thread back to the main thread via a Queue, and have the main thread periodically check for data in the queue using self.root.after():

from Tkinter import *
import tkFont
import os
import glob
import time
import threading
import Image 
import Queue


def update_temp(queue):
    """ Read the temp data. This runs in a background thread. """
    while True:
        #   28-000005c6ba08
        i = "28-000005c6ba08"
        base_dir = '/sys/bus/w1/devices/'
        device_folder = glob.glob(base_dir + i)[0]
        device_file = device_folder + '/w1_slave'

        tempread=round(read_temp(),1)

        # Pass the temp back to the main thread.
        queue.put(tempread)
        time.sleep(5)

class Gui(object):
    def __init__(self, queue):
        self.queue = queue

        #Make the window
        self.root = Tk() 
        self.root.wm_title("Home Management System")
        self.root.minsize(1440,1000)

        self.equipTemp = StringVar()   
        self.equipTemp1 = StringVar()
        self.equipTemp2 = StringVar()       

        self.customFont = tkFont.Font(family="Helvetica", size=16)

        #   1st floor Image
        img = Image.open("HOUSE-PLANS-01.png") 
        photo = ImageTk.PhotoImage(img)

        Label1=Label(self.root, image=photo)
        Label1.place(x=100, y=100)

        #   2nd floor
        img2 = Image.open("HOUSE-PLANS-02.png")
        photo2 = ImageTk.PhotoImage(img2)

        Label1=Label(self.root, image=photo2)
        Label1.place(x=600, y=100)

        #   Basement image
        img3 = Image.open("HOUSE-PLANS-03.png")
        photo3 = ImageTk.PhotoImage(img3)

        Label1=Label(self.root, image=photo3)
        Label1.place(x=100, y=500)

        #   Attic Image
        img4 = Image.open("HOUSE-PLANS-04.png")
        photo4 = ImageTk.PhotoImage(img4)

        Label1=Label(self.root, image=photo4)
        Label1.place(x=600, y=500)

        #   House Isometric Image
        img5 = Image.open("house-iso.png")
        photo5 = ImageTk.PhotoImage(img5)

        Label1=Label(self.root, image=photo5)
        Label1.place(x=1080, y=130)

        #Garage Temp Label
        Label2=Label(self.root, textvariable=self.equipTemp, width=6, justify=RIGHT, font=self.customFont)
        Label2.place(x=315, y=265)

        print "start monitoring and updating the GUI"

        # Schedule read_queue to run in the main thread in one second.
        self.root.after(1000, self.read_queue)

    def read_queue(self):
        """ Check for updated temp data"""
        try:
            temp = self.queue.get_nowait()
            self.equipTemp.set(temp)
        except Queue.Empty:
            # It's ok if there's no data to read.
            # We'll just check again later.
            pass
        # Schedule read_queue again in one second.
        self.root.after(1000, self.read_queue)

if __name__ == "__main__":
    queue = Queue.Queue()
    # Start background thread to get temp data
    t = threading.Thread(target=update_temp, args=(queue,))
    t.start()
    print "starting app"
    # Build GUI object
    gui = Gui(queue)
    # Start mainloop
    gui.root.mainloop()

在实际查看 tkinter 源代码以及 Python 错误跟踪器后，似乎与几乎所有其他 GUI 库不同，tkinter 旨在是线程安全的，只要您在应用程序的主线程中运行主循环.请参阅我在此处添加的答案以获取更多信息，或直接转到 Python 错误跟踪器上有关 tkinter 线程安全的已解决问题此处.如果 tkinter 源码和 Python 的 bug tracker 是正确的，那就意味着只要你在主线程中运行 mainloop，你就可以愉快地直接从你的温度读数中调用 gui.equipTemp.set()线程 - 不需要 Queue.在我的测试中，这确实工作得很好.

After actually taking a look at the tkinter source code, as well as the Python bug tracker, it appears that unlike almost every other GUI library out there, tkinter is intended to be thread-safe, as long you run the mainloop in the main thread of the application. See the answer I added here for more info, or go straight to the resolved issue about tkinter's thread safety on the Python bug tracker here. If the tkinter source and Python's bug tracker are correct, that would mean that as long as you run the mainloop in the main thread, you can happily call gui.equipTemp.set() directly from your temperature reading thread - no Queue required. And in my testing, that did indeed work just fine.

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