从报警处理程序更新共享文件时防止脏读/写

我有一个要求,我的进程需要定期更新一个文件(比如每5秒)。在正常的代码流中,这个文件也被更新了多次。

我使用python警报来中断并定期更新这个共享文件。我正面临着一个脏读的问题,这使我的文件内容混乱。

示例代码:

import signal
import time
import json

class AlarmException(Exception):
    pass

def alarmHandler(signum, frame):
    numbers = read()
    numbers["4"] = "Four"
    write(numbers)
    print(read())
    
def write(content):
    file = open("text.txt", "w")
    file.write(json.dumps(content))
    file.flush()
    
def read():
    file = open("text.txt", "r")
    return(json.load(file))

def dirtyread(timeout=5):
    # Alarm setup, call alarmHandler after 5 seconds
    signal.signal(signal.SIGALRM, alarmHandler)
    signal.alarm(timeout)
    
    # Initialize file
    numbers = {"1": "one", "2": "two"}
    write(numbers)
    
    # Read the file content 
    new_numbers = read()
    
    # Some processing after reading the file content
    time.sleep(7)
    
    # Write new content
    new_numbers["3"] = "Three"
    write(new_numbers)
    print(read())
    
    
dirtyread()

输出:

{'1':'1','2':'2','4':'4'}

{'1':'1','2':'2','3':'3'}