Python加入进程而不会阻止父进程

Question

我正在编写一个程序，它将监视特定目录中包含下载URL的新文件。一旦检测到新文件，它将在父级继续监视目录的同时创建一个新过程来进行实际下载。我正在使用Process来自的界面multiprocessing。我的问题是，除非我调用process.join（），否则子进程仍在运行，但是process.join（）是一个阻止函数，无法实现创建子进程来处理实际下载的目的。

我的问题是，是否有一种以非阻塞方式加入子进程的方法，该方法将允许父进程继续做它的事情？

部分代码：

def main(argv):
  # parse command line args
  ...
  # set up variables
  ...
  watch_dir(watch_dir, download_dir)


def watch_dir(wDir, dDir):
  # Grab the current watch directory listing
  before = dict([(f, None) for f in os.listdir (wDir)])

  # Loop FOREVER
  while 1:
    # sleep for 10 secs
    time.sleep(10)

    # Grab the current dir listing
    after = dict([(f, None) for f in os.listdir (wDir)])

    # Get the list of new files
    added = [f for f in after if not f in before]
    # Get the list of deleted files
    removed = [f for f in before if not f in after]

    if added:
      # We have new files, do your stuff
      print "Added: ", ", ".join(added)

      # Call the new process for downloading
      p = Process(target=child, args=(added, wDir, dDir))
      p.start()
      p.join()

    if removed:
      # tell the user the file was deleted
      print "Removed: ", ", ".join(removed)

    # Set before to the current
    before = after

def child(filename, wDir, dDir):
  # Open filename and extract the url
  ...
  # Download the file and to the dDir directory
  ...
  # Delete filename from the watch directory
  ...
  # exit cleanly
  os._exit(0)

父母等待孩子完成执行，然后再继续执行p.join()（据我所知）是正确的。但这破坏了创造孩子的全部目的。如果我离开了，p.join()那么孩子仍然活跃，并且有一个ps ax | greppython给我’python ‘。

我希望孩子完成自己的工作，然后在不牵扯父母的情况下离开。有办法吗？

Answer 1

您可以设置一个单独的线程来进行连接。让它侦听将子进程句柄推入的队列：

class Joiner(Thread):
    def __init__(self, q):
        self.__q = q
    def run(self):
        while True:
            child = self.__q.get()
            if child == None:
                return
            child.join()

然后，而不是p.join()，执行joinq.put(p)并执行ajoinq.put(None)信号通知线程停止。确保使用FIFO队列。