我有一个不太确定如何解决的小问题。下面是一个最小示例：
我有什么
scan_process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
while(some_criterium):
line = scan_process.stdout.readline()
some_criterium = do_something(line)
我想要什么
scan_process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
while(some_criterium):
line = scan_process.stdout.readline()
if nothing_happens_after_10s:
break
else:
some_criterium = do_something(line)
我从子流程中读取一行并对其进行处理。如果在固定时间间隔后没有线路到达，如何退出？
感谢您的所有答案！
我找到了一种解决问题的方法，只需使用 select.poll 查看标准输出即可。
import select
...
scan_process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
poll_obj = select.poll()
poll_obj.register(scan_process.stdout, select.POLLIN)
while(some_criterium and not time_limit):
poll_result = poll_obj.poll(0)
if poll_result:
line = scan_process.stdout.readline()
some_criterium = do_something(line)
update(time_limit)
这是一个便携式解决方案，它强制执行使用 asyncio 读取单行的超时：
#!/usr/bin/env python3
import asyncio
import sys
from asyncio.subprocess import PIPE, STDOUT
async def run_command(*args, timeout=None):
# Start child process
# NOTE: universal_newlines parameter is not supported
process = await asyncio.create_subprocess_exec(*args,
stdout=PIPE, stderr=STDOUT)
# Read line (sequence of bytes ending with b'n') asynchronously
while True:
try:
line = await asyncio.wait_for(process.stdout.readline(), timeout)
except asyncio.TimeoutError:
pass
else:
if not line: # EOF
break
elif do_something(line):
continue # While some criterium is satisfied
process.kill() # Timeout or some criterion is not satisfied
break
return await process.wait() # Wait for the child process to exit
if sys.platform == "win32":
loop = asyncio.ProactorEventLoop() # For subprocess' pipes on Windows
asyncio.set_event_loop(loop)
else:
loop = asyncio.get_event_loop()
returncode = loop.run_until_complete(run_command("cmd", "arg 1", "arg 2",
timeout=10))
loop.close()
我在Python中使用了一些更通用的东西（如果我没记错的话，也是从Stack Overflow问题中拼凑出来的，但我不记得是哪些问题）。
import thread
from threading import Timer
def run_with_timeout(timeout, default, f, *args, **kwargs):
if not timeout:
return f(*args, **kwargs)
try:
timeout_timer = Timer(timeout, thread.interrupt_main)
timeout_timer.start()
result = f(*args, **kwargs)
return result
except KeyboardInterrupt:
return default
finally:
timeout_timer.cancel()
不过要注意。这使用中断来停止您为其提供的任何功能。对于所有函数来说，这可能不是一个好主意，并且还会阻止您在超时期间使用 Ctrl + C 关闭程序（即 Ctrl + C 将作为超时处理）。
你可以使用它并像这样称呼它：
scan_process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
while(some_criterium):
line = run_with_timeout(timeout, None, scan_process.stdout.readline)
if line is None:
break
else:
some_criterium = do_something(line)
不过，这可能有点矫枉过正。我怀疑你的情况有一个我不知道的更简单的选择。
虽然 Tom 的解决方案有效，但在 C 习语中使用 select() 更紧凑，这相当于您的答案：
from select import select
scan_process = subprocess.Popen(command,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT,
bufsize=1) # Line buffered
while some_criterium and not time_limit:
poll_result = select([scan_process.stdout], [], [], time_limit)[0]
其余的都是一样的。
请参阅pydoc select.select 。
[注意：这是特定于Unix的，其他一些答案也是如此。
[注2：根据OP请求编辑以添加线路缓冲]
[注3：行缓冲可能并非在所有情况下都可靠，导致readline（）阻塞]
一个可移植的解决方案是，如果读取一行的时间太长，则使用线程来终止子进程：
#!/usr/bin/env python3
from subprocess import Popen, PIPE, STDOUT
timeout = 10
with Popen(command, stdout=PIPE, stderr=STDOUT,
universal_newlines=True) as process: # text mode
# kill process in timeout seconds unless the timer is restarted
watchdog = WatchdogTimer(timeout, callback=process.kill, daemon=True)
watchdog.start()
for line in process.stdout:
# don't invoke the watcthdog callback if do_something() takes too long
with watchdog.blocked:
if not do_something(line): # some criterium is not satisfied
process.kill()
break
watchdog.restart() # restart timer just before reading the next line
watchdog.cancel()
其中WatchdogTimer类类似于可以重新启动和/或阻止的threading.Timer：
from threading import Event, Lock, Thread
from subprocess import Popen, PIPE, STDOUT
from time import monotonic # use time.time or monotonic.monotonic on Python 2
class WatchdogTimer(Thread):
"""Run *callback* in *timeout* seconds unless the timer is restarted."""
def __init__(self, timeout, callback, *args, timer=monotonic, **kwargs):
super().__init__(**kwargs)
self.timeout = timeout
self.callback = callback
self.args = args
self.timer = timer
self.cancelled = Event()
self.blocked = Lock()
def run(self):
self.restart() # don't start timer until `.start()` is called
# wait until timeout happens or the timer is canceled
while not self.cancelled.wait(self.deadline - self.timer()):
# don't test the timeout while something else holds the lock
# allow the timer to be restarted while blocked
with self.blocked:
if self.deadline <= self.timer() and not self.cancelled.is_set():
return self.callback(*self.args) # on timeout
def restart(self):
"""Restart the watchdog timer."""
self.deadline = self.timer() + self.timeout
def cancel(self):
self.cancelled.set()
尝试使用 signal.alarm：
#timeout.py
import signal, sys
def timeout(sig, frm):
print "This is taking too long..."
sys.exit(1)
signal.signal(signal.SIGALRM, timeout)
signal.alarm(10)
byte = 0
while 'IT' not in open('/dev/urandom').read(2):
byte += 2
print "I got IT in %s byte(s)!" % byte
几次运行以显示它有效：
$ python timeout.py
This is taking too long...
$ python timeout.py
I got IT in 4672 byte(s)!
有关更详细的示例，请参阅指南。
使用线程
import subprocess, threading, time
def _watcher(proc, delay):
time.sleep(delay)
proc.kill()
try:
scan_process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
threading.Thread(target = _watcher, args = (scan_process, 10)).start()
while(some_criterium):
line = scan_process.stdout.readline()
if nothing_happens_after_10s:
break
else:
some_criterium = do_something(line)
except Exception as e:
print(e)
另请参阅如何在超时的情况下运行进程，并在运行时仍然获取标准输出