運行子流程時檢查條件

Question

我正在使用subprocess.Popen（）執行命令。 我想在執行其余代碼之前等待進程完成，但是同時我想在運行子進程2分鍾后檢查生成的文件的狀態。 如果文件大小為零，那么我想停止該過程。 目前，我的代碼如下。 有沒有更聰明的方法可以做到這一點？

  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

在全球范圍內，您的代碼對我來說看起來不錯。 只有一些細節：

1. 在(time.time()-start_time)//60>1 ，我認為//沒用，因為您不一定需要舍棄結果並將除法lhs的結果轉換為整數。 比較起來應該保持所有浮動，這是所有基本的機器邏輯；
2. 您可以通過使用while process.returncode is not None:…來更改循環條件來避免從無限循環中中斷while process.returncode is not None:…
3. 為了使它更簡單，我實際上要循環直到文件大小為!=0 ，然后在循環之后調用process.wait() 。
4. 這將是使用while/else構造的好方案

因此，有一個改進是，您可以在過程完成之后（無論成功還是失敗）進行處理（例如清理或重試...）：

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
    […]

或另一個好的選擇是引發異常：

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為空的情況下在2分鍾內殺死子進程（我假設outputfilename被某個外部進程修改了），則可以使用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()
    ...

此代碼分別收集stdout / stderr，並且避免了問題代碼中可能出現的死鎖。