在 python 中使用 FIFO 进行输入和输出

Question

为了与启动一次并在单独进程中运行的 shell 通信，我使用了 Popen from subprocess.

import os
from subprocess import Popen, PIPE

def server():
    FIFO_PATH = '/tmp/my_fifo'
    FIFO_PATH2 = '/tmp/in_fifo'
    if os.path.exists(FIFO_PATH):
        os.unlink(FIFO_PATH)
    if os.path.exists(FIFO_PATH2):
        os.unlink(FIFO_PATH2)

    if not os.path.exists(FIFO_PATH2):
        os.mkfifo(FIFO_PATH2)
        in_fifo = open(FIFO_PATH2, 'rw+')
        print "in_fifo:", in_fifo

    if not os.path.exists(FIFO_PATH):
        os.mkfifo(FIFO_PATH)
        my_fifo = open(FIFO_PATH, 'rw+')
        print "my_fifo:", my_fifo

    p = Popen(['python', '-u', 'shell.py'], shell=False, stdin=in_fifo, stdout=my_fifo)

def read():
    FIFO_PATH = '/tmp/my_fifo'
    i=0
    while i < 10:
        ++i
        print i, open(FIFO_PATH, 'r').readline()

def write(input):
    FIFO_PATH2 = '/tmp/in_fifo'

    pipe = open(FIFO_PATH2, 'w+')
    pipe.write(input+'\n')

def test():
    server()
    write('test')
    read()

和shell.py

Input = ' '
print 'shell called'
while Input!= 'z':
    Input=raw_input()
    print 'input ', Input

    if Input != '':
        if Input == 'test':
            print 'Yeehhaaaaa it works'

所以调用 test() 给出以下结果

in_fifo: <open file '/tmp/in_fifo', mode 'rw+' at 0x7f0a4e17ed20>
my_fifo: <open file '/tmp/my_fifo', mode 'rw+' at 0x7f0a4e17edb0>
0 shell called

0 input  test

问题

为什么只打印第一行？如何打印所有行？

我也不确定如何正确使用 FIFO。也许有更好的方法来完成这项工作。我愿意接受任何建议。

使用p调用p.stdin.write()和p.stdout.readline()对我来说不是解决方案，因为我必须在没有实例[=18=的情况下调用javascript中的函数].

Answer 1

来自 mkfifo 的手册页：

Opening a FIFO for reading normally blocks until some other process opens the same FIFO for writing, and vice versa. See fifo(7) for nonblocking handling of FIFO special files.

因此第二次打开FIFO进行读取时，调用阻塞。这可以在按下 Ctrl+C 后的回溯中看到：

^CTraceback (most recent call last):
0
Traceback (most recent call last):
  File "shell_fifo.py", line 51, in <module>
  File "shell.py", line 4, in <module>
    test()
  File "shell_fifo.py", line 48, in test
        read()
  File "shell_fifo.py", line 29, in read
    print i, open(FIFO_PATH, 'r').readline() # read() is blocked here
KeyboardInterrupt
Input=raw_input()
KeyboardInterrupt

更改您的 read 函数，使其只打开 FIFO 一次：

def read():
    FIFO_PATH = '/tmp/my_fifo'
    i = 0
    with open(FIFO_PATH, 'r') as read_fifo:
        while i < 10:
            i += 1
            print i, read_fifo.readline().rstrip()

您应该看到这样的输出：

in_fifo: <open file '/tmp/in_fifo', mode 'rw+' at 0x7f1ba655b5d0>
my_fifo: <open file '/tmp/my_fifo', mode 'rw+' at 0x7f1ba655b540>
1 shell called
2 input  test
3 Yeehhaaaaa it works

在 python 中使用 FIFO 进行输入和输出

using FIFOs for input and output in python

python

fifo

mkfifo