并行的 Python 子进程

问题描述

我想并行运行多个进程，并能够随时获取标准输出.我该怎么做?我需要为每个 subprocess.Popen() 调用运行线程吗?

I want to run many processes in parallel with ability to take stdout in any time. How should I do it? Do I need to run thread for each subprocess.Popen() call, a what?

推荐答案

你可以在一个线程中完成.

You can do it in a single thread.

假设您有一个随机打印行的脚本:

Suppose you have a script that prints lines at random times:

#!/usr/bin/env python
#file: child.py
import os
import random
import sys
import time

for i in range(10):
    print("%2d %s %s" % (int(sys.argv[1]), os.getpid(), i))
    sys.stdout.flush()
    time.sleep(random.random())

并且您想在输出可用时立即收集输出，您可以使用 select 在 POSIX 系统上作为 @zigg建议:

And you'd like to collect the output as soon as it becomes available, you could use select on POSIX systems as @zigg suggested:

#!/usr/bin/env python
from __future__ import print_function
from select     import select
from subprocess import Popen, PIPE

# start several subprocesses
processes = [Popen(['./child.py', str(i)], stdout=PIPE,
                   bufsize=1, close_fds=True,
                   universal_newlines=True)
             for i in range(5)]

# read output
timeout = 0.1 # seconds
while processes:
    # remove finished processes from the list (O(N**2))
    for p in processes[:]:
        if p.poll() is not None: # process ended
            print(p.stdout.read(), end='') # read the rest
            p.stdout.close()
            processes.remove(p)

    # wait until there is something to read
    rlist = select([p.stdout for p in processes], [],[], timeout)[0]

    # read a line from each process that has output ready
    for f in rlist:
        print(f.readline(), end='') #NOTE: it can block

更便携的解决方案(应该适用于 Windows、Linux、OSX)可以为每个进程使用读取器线程，请参阅 非阻塞在 python 中读取 subprocess.PIPE.

A more portable solution (that should work on Windows, Linux, OSX) can use reader threads for each process, see Non-blocking read on a subprocess.PIPE in python.

这里是 os.pipe() 基于 Unix 和 Windows 的解决方案:

Here's os.pipe()-based solution that works on Unix and Windows:

#!/usr/bin/env python
from __future__ import print_function
import io
import os
import sys
from subprocess import Popen

ON_POSIX = 'posix' in sys.builtin_module_names

# create a pipe to get data
input_fd, output_fd = os.pipe()

# start several subprocesses
processes = [Popen([sys.executable, 'child.py', str(i)], stdout=output_fd,
                   close_fds=ON_POSIX) # close input_fd in children
             for i in range(5)]
os.close(output_fd) # close unused end of the pipe

# read output line by line as soon as it is available
with io.open(input_fd, 'r', buffering=1) as file:
    for line in file:
        print(line, end='')
#
for p in processes:
    p.wait()

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