os.chdir() 导致 python 多线程出现意外行为

Question

我是 Python 多线程的新手。在我的代码中，我调用了一个函数，该函数使用 chdir() 更改其工作目录，如下所示。

import threading
import os
import shutil

def sayHello(dirName,userName):
    if not os.path.exists(dirName):
        os.makedirs(dirName)
    else:
        shutil.rmtree(dirName)
        os.makedirs(dirName)

    os.chdir(dirName)
    f = open("hello.txt","w")
    f.write("Hello %s\n" %userName)
    f.close()

thread1 = threading.Thread(target=sayHello,args=('hiDir1','Andrew'))
thread2 = threading.Thread(target=sayHello,args=('hiDir2','Michael'))

thread1.start()
thread2.start()

thread1.join()
thread2.join()

预期的行为是，

1. thread1 : 创建“hiDir1”目录，在“hiDir1”中创建“hello.txt”，在“hello.txt”中打印“Hello Andrew”
2. thread2 : 创建“hiDir2”目录，在“hiDir2”中创建“hello.txt”并在“hello.txt”中打印“Hello Michael”

当我第一次运行代码时，它运行没有错误。所有文件均已正确生成。但是“hiDir2”在“hiDir1”里面。

没有删除生成的文件，我第二次运行它。两个目录都在那里。但只有“hiDir2”有正确的文本文件，文件上印有正确的信息。 “hiDir1”没有文本文件。弹出以下错误。

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "threadingError.py", line 9, in sayHello
    shutil.rmtree(dirName)
  File "/usr/lib/python3.5/shutil.py", line 478, in rmtree
    onerror(os.rmdir, path, sys.exc_info())
  File "/usr/lib/python3.5/shutil.py", line 476, in rmtree
    os.rmdir(path)
FileNotFoundError: [Errno 2] No such file or directory: 'hiDir1'ode here

当我第三次运行它而不删除文件时，第二次运行反之亦然。两个目录都在那里。但只有“hiDir1”具有正确输出的文本文件。 'hiDir2' 是空的。有以下错误消息。

Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python3.5/threading.py", line 914, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.5/threading.py", line 862, in run
    self._target(*self._args, **self._kwargs)
  File "threadingError.py", line 12, in sayHello
    os.chdir(dirName)
FileNotFoundError: [Errno 2] No such file or directory: 'hiDir2'

当我重复运行此程序时，第二次和第三次发生恰好一个接一个。（怎么会发生这种情况？每次都应该给出相同的输出，不是吗？）

据我了解，问题出在“chdir()”上。所以我重新安排了代码以摆脱'chdir（）'，如下所示。

import threading
import os
import shutil

def sayHello(dirName,userName):
    if not os.path.exists(dirName):
        os.makedirs(dirName)
    else:
        shutil.rmtree(dirName)
        os.makedirs(dirName)

    filePath1 = dirName+'/hello.txt'
    print("filePath1: ", filePath1)
    # os.chdir(dirName)
    f = open(dirName+'/hello.txt',"w")
    f.write("Hello %s\n" %userName)
    f.close()

thread1 = threading.Thread(target=sayHello,args=('hiDir1','Andrew'))
thread2 = threading.Thread(target=sayHello,args=('hiDir2','Michael'))

thread1.start()
thread2.start()

thread1.join()
thread2.join()

然后，没有问题。代码按预期运行。在 python 多线程中使用 os.chdir() 有什么问题吗？这是python线程模块中的错误吗？

谢谢。

Answer 1

这个怎么样：

import threading

from pathlib import Path


def say_hello(dir_name, username):
    """
    Creates dir_name (and its parents dirs) if not dir_name does not exist,
    then it creates a hello.txt file with the legent: 'Hello <username>'

    Examples:

    >>> say_hello('say_hello/slackmart', 'SLACKMART')
    say_hello/slackmart not found. Creating say_hello/slackmart
    Writing to say_hello/slackmart/hello.txt
    """
    path = Path(dir_name)
    if not path.exists():
        print(f'{dir_name} not found. Creating {dir_name}')
        path.mkdir(parents=True)
    else:
        # I wouldn't remove the dir_name path here as it could be dangerous
        print(f'Found {dir_name}')

    file_path = path / Path('hello.txt')  # Yes, you can join paths by using /
    print('Writing to', file_path)
    file_path.write_text(f'Hello {username}\n')


if __name__ == '__main__':
    andrew = threading.Thread(target=say_hello, args=('hiAndrewDir', 'Andrew'))
    michael = threading.Thread(target=say_hello, args=('hiMichaelDir', 'Michael'))

    andrew.start()
    michael.start()

    andrew.join()
    michael.join()

演示时间：

$ python3 sayhello.py

https://docs.python.org/3/library/pathlib.html