对子进程的非阻塞读取.Python中的PIPE

问题描述

我正在使用子流程模块来启动子流程并连接到其输出流(标准输出).我希望能够在其标准输出上执行非阻塞读取.有没有一种方法可以使.readline成为非阻塞的，或者在调用.readline之前检查流中是否有数据?我希望这是可移植的，或者至少要在Windows和Linux下工作.

I'm using the subprocess module to start a subprocess and connect to its output stream (standard output). I want to be able to execute non-blocking reads on its standard output. Is there a way to make .readline non-blocking or to check if there is data on the stream before I invoke .readline? I'd like this to be portable or at least work under Windows and Linux.

这是我现在的操作方式(如果没有可用数据，它将阻塞在.readline上):

Here is how I do it for now (it's blocking on the .readline if no data is available):

p = subprocess.Popen('myprogram.exe', stdout = subprocess.PIPE)
output_str = p.stdout.readline()

推荐答案

， select ， asyncproc 在这种情况下无济于事.

fcntl, select, asyncproc won't help in this case.

一种可靠的读取流而不受操作系统限制的方法是使用 Queue.get_nowait() :

A reliable way to read a stream without blocking regardless of operating system is to use Queue.get_nowait():

import sys
from subprocess import PIPE, Popen
from threading  import Thread

try:
    from queue import Queue, Empty
except ImportError:
    from Queue import Queue, Empty  # python 2.x

ON_POSIX = 'posix' in sys.builtin_module_names

def enqueue_output(out, queue):
    for line in iter(out.readline, b''):
        queue.put(line)
    out.close()

p = Popen(['myprogram.exe'], stdout=PIPE, bufsize=1, close_fds=ON_POSIX)
q = Queue()
t = Thread(target=enqueue_output, args=(p.stdout, q))
t.daemon = True # thread dies with the program
t.start()

# ... do other things here

# read line without blocking
try:  line = q.get_nowait() # or q.get(timeout=.1)
except Empty:
    print('no output yet')
else: # got line
    # ... do something with line

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