运行子流程时检查条件

Question

我正在使用subprocess.Popen（）执行命令。 我想在执行其余代码之前等待进程完成，但是同时我想在运行子进程2分钟后检查生成的文件的状态。 如果文件大小为零，那么我想停止该过程。 目前，我的代码如下。 有没有更聪明的方法可以做到这一点？

  def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while True:
     process.poll()
     if not Is_Working:
         #allow 2 minutes for the process to create results
         if process.returncode == None and (time.time()-start_time)//60>1:
             Is_Working=True
             if (os.stat(outputfilename)[6]==0):
                 process.kill()
                 return
     if process.returncode != None: 
         break

    output, errors=process.communicate()

Answer 1

在全球范围内，您的代码对我来说看起来不错。 只有一些细节：

1. 在(time.time()-start_time)//60>1 ，我认为//没用，因为您不一定需要舍弃结果并将除法lhs的结果转换为整数。 比较起来应该保持所有浮动，这是所有基本的机器逻辑；
2. 您可以通过使用while process.returncode is not None:…来更改循环条件来避免从无限循环中中断while process.returncode is not None:…
3. 为了使它更简单，我实际上要循环直到文件大小为!=0 ，然后在循环之后调用process.wait() 。
4. 这将是使用while/else构造的好方案

因此，有一个改进是，您可以在过程完成之后（无论成功还是失败）进行处理（例如清理或重试...）：

def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while process.returncode == None:
        process.poll()
        #allow 2 minutes for the process to create results
        if (time.time()-start_time)/60 > 1:
            if (os.stat(outputfilename)[6]==0):
                process.kill()
                break
    else:
        # the process has not been killed
        # wait until it finishes
        process.wait()
        output, errors=process.communicate()
        # do stuff with the output
        […]

    # here the process may have been killed or not
    […]

或另一个好的选择是引发异常：

def execute(command,outputfilename):
    process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    start_time=time.time()
    Is_Working=False
    while process.returncode == None:
        process.poll()
        #allow 2 minutes for the process to create results
        if (time.time()-start_time)/60 > 1:
            if (os.stat(outputfilename)[6]==0):
                process.kill()
                raise Exception("Process has failed to do its job")
    # the process has not been killed
    # wait until it finishes
    process.wait()
    output, errors=process.communicate()
    # do stuff with the output
    […]

HTH

Answer 2

要在outputfilename为空的情况下在2分钟内杀死子进程（我假设outputfilename被某个外部进程修改了），则可以使用threading.Timer ：

import os
from subprocess import Popen, PIPE
from threading import Timer

def kill_if_empty(proc, filename):
    if proc.poll() is None and os.path.getsize(filename) == 0:
       proc.kill()

def execute(command, outputfilename):
    p = Popen(command, stdout=PIPE, stderr=PIPE)
    Timer(2*60, kill_if_empty, [p, outputfilename]).start()
    output, errors = p.communicate()
    ...

此代码分别收集stdout / stderr，并且避免了问题代码中可能出现的死锁。