toctou_race_condition.py

# Demonstration of a time of check to time of use (toutou) race condition

import os
import time
from threading import Thread


class ReadFileThread(Thread):

    def __init__(self, file_name):
        self.file_name = file_name
        super().__init__()

    def run(self):
        if os.path.isfile(self.file_name):
            print('{file_name} exists'.format(file_name=self.file_name))
            time.sleep(0.1)
            file_contents = open(self.file_name, 'r').read()
            print(file_contents)


class RemoveFileThread(Thread):

    def __init__(self, file_name):
        self.file_name = file_name
        super().__init__()

    def run(self):
        print('Deleting {file_name}'.format(file_name=self.file_name))
        os.remove(self.file_name)


def demonstrate_toctou_race_condition():
    file_name = 'tmp'
    open(file_name, 'a').close() # create empty file
    read_file_thread = ReadFileThread(file_name)
    remove_file_thread = RemoveFileThread(file_name)
    read_file_thread.start()
    remove_file_thread.start()


demonstrate_toctou_race_condition()