实时拦截子流程输出的问题

2022-01-18 00:00:00 python python-3.x tkinter subprocess stdout

问题描述

我在堆栈溢出上花了大约 6 个小时，重写了我的 python 代码并试图让它工作.它只是没有.不管我做什么.

I've spent about 6 hours on stack overflow, rewriting my python code and trying to get this to work. It just doesn't tho. No matter what I do.

目标:让子进程的输出实时显示在 tkinter 文本框中.

The goal: Getting the output of a subprocess to appear in real time in a tkinter text box.

问题:我不知道如何使 Popen 实时工作.它似乎挂起，直到该过程完成.(自行运行，过程完全按预期运行，所以只是这个东西有错误)

The issue: I can't figure out how to make the Popen work in real time. It seems to hang until the process is complete. (Run on its own, the process works completely as expected, so it's just this thing that has the error)

相关代码:

import os
import tkinter
import tkinter.ttk as tk
import subprocess

class Application (tk.Frame):
    process = 0
    def __init__ (self, master=None):
        tk.Frame.__init__(self, master)
        self.grid()
        self.createWidgets()

    def createWidgets (self):
        self.quitButton = tk.Button(self, text='Quit', command=self.quit)
        self.quitButton.grid()
        self.console = tkinter.Text(self)
        self.console.config(state=tkinter.DISABLED)
        self.console.grid()

    def startProcess (self):
        dir = "C:/folder/"
        self.process = subprocess.Popen([ "python", "-u", dir + "start.py" ], stdout=subprocess.PIPE, stdin=subprocess.PIPE, stderr=subprocess.PIPE, cwd=dir)
        self.updateLines()

    def updateLines (self):
        self.console.config(state=tkinter.NORMAL)
        while True:
            line = self.process.stdout.readline().decode().rstrip()
            if line == '' and self.process.poll() != None:
                break
            else: 
                self.console.insert(tkinter.END, line + "
")
        self.console.config(state=tkinter.DISABLED)
        self.after(1, self.updateLines)

app = Application()
app.startProcess()
app.mainloop()

另外，如果我的代码写得不好，请随意销毁我的代码.这是我的第一个 python 项目，我不希望对语言有任何好处.

Also, feel free to destroy my code if it's written poorly. This is my first python project, I don't expect to be any good at the language yet.

解决方案

这里的问题是 process.stdout.readline() 会阻塞，直到有完整的行可用.这意味着条件 line == '' 在进程退出之前永远不会满足.您有两种选择.

The problem here is that process.stdout.readline() will block until a full line is available. This means the condition line == '' will never be met until the process exits. You have two options around this.

首先，您可以将 stdout 设置为非阻塞并自己管理缓冲区.它看起来像这样.正如 Terry Jan Reedy 指出的，这是一个仅适用于 Unix 的解决方案.应该首选第二种选择.

First you can set stdout to non-blocking and manage a buffer yourself. It would look something like this. As Terry Jan Reedy pointed out this is a Unix only solution. The second alternative should be preferred.

import fcntl
...

    def startProcess(self):
        self.process = subprocess.Popen(['./subtest.sh'],
            stdout=subprocess.PIPE,
            stdin=subprocess.PIPE,
            stderr=subprocess.PIPE,
            bufsize=0) # prevent any unnecessary buffering

        # set stdout to non-blocking
        fd = self.process.stdout.fileno()
        fl = fcntl.fcntl(fd, fcntl.F_GETFL)
        fcntl.fcntl(fd, fcntl.F_SETFL, fl | os.O_NONBLOCK)

        # schedule updatelines
        self.after(100, self.updateLines)

    def updateLines(self):
        # read stdout as much as we can
        line = ''
        while True:
            buff = self.process.stdout.read(1024)
            if buff:
                buff += line.decode()
            else:
                break

        self.console.config(state=tkinter.NORMAL)
        self.console.insert(tkinter.END, line)
        self.console.config(state=tkinter.DISABLED)

        # schedule callback
        if self.process.poll() is None:
            self.after(100, self.updateLines)

第二种选择是让一个单独的线程将行读入队列.然后从队列中弹出更新行.它看起来像这样

The second alternative is to have a separate thread read the lines into a queue. Then have updatelines pop from the queue. It would look something like this

from threading import Thread
from queue import Queue, Empty

def readlines(process, queue):
    while process.poll() is None:
        queue.put(process.stdout.readline())
...

    def startProcess(self):
        self.process = subprocess.Popen(['./subtest.sh'],
            stdout=subprocess.PIPE,
            stdin=subprocess.PIPE,
            stderr=subprocess.PIPE)

        self.queue = Queue()
        self.thread = Thread(target=readlines, args=(self.process, self.queue))
        self.thread.start()

        self.after(100, self.updateLines)

    def updateLines(self):
        try:
            line = self.queue.get(False) # False for non-blocking, raises Empty if empty
            self.console.config(state=tkinter.NORMAL)
            self.console.insert(tkinter.END, line)
            self.console.config(state=tkinter.DISABLED)
        except Empty:
            pass

        if self.process.poll() is None:
            self.after(100, self.updateLines)

线程路由可能更安全.我不确定将 stdout 设置为非阻塞是否适用于所有平台.

The threading route is probably safer. I'm not positive that setting stdout to non-blocking will work on all platforms.

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