Python3并发写文件

使用python2在进行并发写的时候，发现文件会乱掉，就是某一行中间会插入其他行的内容。

但是在使用python3进行并发写的时候，无论是多进程，还是多线程，都没有出现这个问题，难道是python3的特性吗？

import time

import os

import multiprocessing

from multiprocessing.dummy import Pool as ThreadPool

def write(val, file):

    w = open(file, "a")

    for i in range(100):

        w.write("%s\n" % val)

        time.sleep(0.001)

def thread_write(file):

    res, pools = [], ThreadPool(10)

    for i in range(10):

        val = str(i) * 1000

        res.append(pools.apply_async(func=write, args=(val, file, )))

    while res:

        for ret in res:

            if ret.ready():

                res.remove(ret)

        time.sleep(0.01)

def mutil_write(file):

    pools = multiprocessing.Pool(processes=10)

    res = []

    for i in range(100):

        res.append(pools.apply_async(thread_write, args=(file, )))

    while res:

        for ret in res:

            if ret.ready():

                res.remove(ret)

        time.sleep(0.01)

if __name__ == '__main__':

    file = "./write_test"

    mutil_write(file)

    with open(file) as fb:

        lines = 0

        line_len = []

        for line in fb:

            lines += 1

            line = line.strip()

            line_len.append(len(line))

            if len(line) != 1000:

                raise(Exception("error line: %s, len: %d" % (line, len(line))))

        print("lines:%d, max len:%d, min:%d, avg:%.2f" % (lines, max(line_len), min(line_len), sum(line_len)/len(line_len)))

    os.remove(file)

上面代码，多进程并发写结束后，校验每一行的长度是否是设置好的长度。用python3反复运行，均通过测试没有异常。

$ python3 --version

Python 3.7.4

$ python3 t.py

lines:10000, max len:1000, min:1000, avg:1000.00

如果用python2，则会出现异常：

$ python2 --version

Python 2.7.15

$ python2 t.py

Traceback (most recent call last):

  File "t.py", line 49, in <module>

    raise(Exception("error line: %s, len: %d" % (line, len(line))))

Exception: error line: 333333333333333333333333333333333333333333333333333333333333333333333333333333333333333333330000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000, len: 1092