子进程stdin缓冲区未在bufsize = 1的换行符上刷新 [英] subprocess stdin buffer not flushing on newline with bufsize=1

问题描述

我有两个小python文件，第一个使用input读取一行，然后打印另一行

I have two small python files, the first reads a line using input and then prints another line

a = input()
print('complete')

第二次尝试将此操作作为子进程

The second attempts to run this as a subprocess

import subprocess

proc = subprocess.Popen('./simp.py',
                        stdout=subprocess.PIPE,
                        stdin=subprocess.PIPE,
                        bufsize=1)
print('writing')
proc.stdin.write(b'hey\n')
print('reading')
proc.stdout.readline()

上面的脚本将先打印正在书写"，然后显示正在阅读"，然后挂起.起初我以为这是标准输出缓冲问题，所以我将bufsize=1更改为bufsize=0，这确实解决了该问题.但是，似乎是导致问题的标准输入.

The above script will print "writing" then "reading" but then hang. At first I thought this was a stdout buffering issue, so I changed bufsize=1 to bufsize=0, and this does fix the problem. However, it seems it's the stdin that's causing the problem.

对于bufsize=1，如果我在写操作下方添加proc.stdin.flush()，则该过程将继续.这两种方法都显得笨拙，因为(1)未缓冲的流很慢(2)在所有地方添加刷新都很容易出错.为什么上述write不能在换行符上刷新?文档说bufsize是在为子进程创建stdin，stdout和stderr流时使用的，那么是什么原因导致写操作不能在换行符上刷新?

With bufsize=1, if I add proc.stdin.flush() below the write, the process continues. Both of these approaches seem clumsy since (1) unbuffered streams are slow (2) adding flushes everywhere is error-prone. Why does the above write not flush on a newline? The docs say that bufsize is used when creating stdin, stdout, and stderr stream for the subprocess, so what's causing the write to not flush on the newline?

推荐答案

来自文档:"1表示行缓冲(仅当Universal_newlines = True，即在文本模式下可用)" .这有效:

import subprocess

proc = subprocess.Popen('./simp.py',
                        stdout=subprocess.PIPE,
                        stdin=subprocess.PIPE,
                        bufsize=1,
                        universal_newlines=True)

print('writing')
proc.stdin.write('hey\n')
print('reading')
proc.stdout.readline()

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