Python,Popen和select - 等待进程终止或超时

Question

我使用以下命令运行子进程:

  p = subprocess.Popen("subprocess", 
                       stdout=subprocess.PIPE, 
                       stderr=subprocess.PIPE, 
                       stdin=subprocess.PIPE)

此子进程可以立即退出stderr上的错误,也可以继续运行.我想检测这些条件中的任何一个 - 后者等待几秒钟.

我试过这个:

  SECONDS_TO_WAIT = 10
  select.select([], 
                [p.stdout, p.stderr], 
                [p.stdout, p.stderr],
                SECONDS_TO_WAIT)

但它只是返回:

  ([],[],[])

无论哪种条件.我能做什么？

Answer 1

您是否尝试过使用Popen.Poll()方法.你可以这样做:

p = subprocess.Popen("subprocess", 
                   stdout=subprocess.PIPE, 
                   stderr=subprocess.PIPE, 
                   stdin=subprocess.PIPE)

time.sleep(SECONDS_TO_WAIT)
retcode = p.poll()
if retcode is not None:
   # process has terminated

这将使您始终等待10秒,但如果失败案例很少,则会在所有成功案例中摊销.

编辑:

怎么样:

t_nought = time.time()
seconds_passed = 0

while(p.poll() is not None and seconds_passed < 10):
    seconds_passed = time.time() - t_nought

if seconds_passed >= 10:
   #TIMED OUT

这是一个忙碌的等待的丑陋,但我认为它完成了你想要的.

另外再看一下select call文档,我想你可能想要改变它如下:

SECONDS_TO_WAIT = 10
  select.select([p.stderr], 
                [], 
                [p.stdout, p.stderr],
                SECONDS_TO_WAIT)

由于您通常希望从stderr读取,因此您想知道何时可以读取(即故障情况).

我希望这有帮助.

Answer 2

这就是我提出的.在需要时工作,不需要在进程上超时,但是使用半忙循环.

def runCmd(cmd, timeout=None):
    '''
    Will execute a command, read the output and return it back.

    @param cmd: command to execute
    @param timeout: process timeout in seconds
    @return: a tuple of three: first stdout, then stderr, then exit code
    @raise OSError: on missing command or if a timeout was reached
    '''

    ph_out = None # process output
    ph_err = None # stderr
    ph_ret = None # return code

    p = subprocess.Popen(cmd, shell=True,
                         stdout=subprocess.PIPE,
                         stderr=subprocess.PIPE)
    # if timeout is not set wait for process to complete
    if not timeout:
        ph_ret = p.wait()
    else:
        fin_time = time.time() + timeout
        while p.poll() == None and fin_time > time.time():
            time.sleep(1)

        # if timeout reached, raise an exception
        if fin_time < time.time():

            # starting 2.6 subprocess has a kill() method which is preferable
            # p.kill()
            os.kill(p.pid, signal.SIGKILL)
            raise OSError("Process timeout has been reached")

        ph_ret = p.returncode


    ph_out, ph_err = p.communicate()

    return (ph_out, ph_err, ph_ret)