python中subprocess.PIPE上的非阻塞读取

问题描述

我正在使用来启动子流程并连接到它的输出流（stdout）。我希望能够在其stdout上执行非阻塞读取。有没有办法让.readline非阻塞或在我调用 .readline 之前检查流上是否有数据？我希望这是可移植的，或至少在Windows和Linux下工作。

I'm using the subprocess module to start a subprocess and connect to it's output stream (stdout). I want to be able to execute non-blocking reads on its stdout. 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.

这是我现在的工作方式（它在 .readline 如果没有数据可用）：

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

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

推荐答案

，，在这种情况下无效。

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

无论操作系统如何，无阻塞地读取流的可靠方法是使用：

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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