在并发环境中追加到文件末尾

问题描述

如果以下多个(示例)程序同时运行，需要采取哪些步骤来确保完整​​"行总是正确附加到文件末尾.

What steps need to be taken to ensure that "full" lines are always correctly appended to the end of a file if multiple of the following (example) program are running concurrently.

#!/usr/bin/env python
import random
passwd_text=open("passwd.txt","a+")
u=("jsmith:x:1001:1000:Joe Smith,Room 1007,[phone],[phone],[email protected]:/home/jsmith:/bin/sh",
  "jdoe:x:1002:1000:Jane Doe,Room 1004,[phone],[phone],[email protected]:/home/jdoe:/bin/sh",
  "xyz:x:1003:1000:X Yz,Room 1003,[phone],[phone],[email protected]:/home/xyz:/bin/sh")
for i in range(random.randint(1,2)):
  print >> passwd_text, random.choice(u)
passwd_text.close()

而且:即使磁盘已满或已设置ulimit -f"，也能保证全有或全无"追加(在 linux/unix 上)?

And: Can an "all or nothing" append be guaranteed (on linux/unix) even if the the disk becomes full, or "ulimit -f" has been set?

(注意类似的问题:如何附加到文件?)

推荐答案

我觉得这个bug"的讨论 在 python 的正常 open 函数中表明你没有得到 POSIX 原子保证，但如果你使用

I think the discussion of this "bug" in python's normal open function suggests that you don't get the POSIX atomic guarantee, but you do if you use

with io.open('myfile', 'a') as f:
    f.write('stuff')

http://docs.python.org/2/library/io.html#io.open

如果操作系统正确地实现了它的写入系统调用...

if the operating system implements its write sys call correctly...

http://bugs.python.org/issue15723

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