python - 如何中断/停止/结束挂起的多线程 python 程序

Question

我有一个 python 程序实现了这样的线程:

   class Mythread(threading.Thread):
        def __init__(self, name, q):
            threading.Thread.__init__(self)
            self.name = name
            self.q = q

        def run(self):
            print "Starting %s..." % (self.name)
            while True:
                ## Get data from queue
                data = self.q.get()
                ## do_some_processing with data ###
                process_data(data)
                ## Mark Queue item as done
                self.q.task_done()
            print "Exiting %s..." % (self.name)


    def call_threaded_program():
        ##Setup the threads. Define threads,queue,locks 
        threads = []    
        q = Queue.Queue()
        thread_count = n #some number
        data_list = [] #some data list containing data

        ##Create Threads
        for thread_id in range(1, thread_count+1):
            thread_name = "Thread-" + str(thread_id)
            thread = Mythread(thread_name,q)
            thread.daemon = True
            thread.start()

        ##Fill data in Queue
        for data_item in data_list:
            q.put(data_item)

        try:
            ##Wait for queue to be exhausted and then exit main program
            q.join()
        except (KeyboardInterrupt, SystemExit) as e:
            print "Interrupt Issued. Exiting Program with error state: %s"%(str(e))
            exit(1)

call_threaded_program() 是从不同的程序调用的。

我的代码在正常情况下工作。但是，如果其中一个线程发生错误/异常，则程序会卡住(因为队列连接会无限阻塞)。我能够退出该程序的唯一方法是关闭终端本身。

当线程退出时，终止该程序的最佳方法是什么？有没有一种干净(实际上我会采取任何方式)的方式来做到这一点？我知道这个问题已经被问过很多次了，但我仍然找不到令人信服的答案。如果有任何帮助，我将不胜感激。

编辑:我尝试删除队列中的连接并使用全局退出标志，如 Is there any way to kill a Thread in Python? 中所建议的那样但是，现在的行为太奇怪了，我无法理解发生了什么。

    import threading
    import Queue
    import time

    exit_flag = False

    class Mythread (threading.Thread):
        def __init__(self,name,q):
            threading.Thread.__init__(self)
            self.name = name
            self.q = q

        def run(self):
            try:    
                # Start Thread
                print "Starting %s...."%(self.name)
                # Do Some Processing
                while not exit_flag:
                    data = self.q.get()
                    print "%s processing %s"%(self.name,str(data))
                    self.q.task_done()
                # Exit thread
                print "Exiting %s..."%(self.name)
            except Exception as e:
                print "Exiting %s due to Error: %s"%(self.name,str(e))


    def main():
        global exit_flag

        ##Setup the threads. Define threads,queue,locks 
        threads = []    
        q = Queue.Queue()
        thread_count = 20
        data_list = range(1,50)

        ##Create Threads
        for thread_id in range(1,thread_count+1):
            thread_name = "Thread-" + str(thread_id)
            thread = Mythread(thread_name,q)
            thread.daemon = True
            threads.append(thread)
            thread.start()

        ##Fill data in Queue
        for data_item in data_list:
          q.put(data_item)


        try:
          ##Wait for queue to be exhausted and then exit main program
          while not q.empty():
            pass

          # Stop the threads
          exit_flag = True

          # Wait for threads to finish
          print "Waiting for threads to finish..."
          while threading.activeCount() > 1:
            print "Active Threads:",threading.activeCount()
            time.sleep(1)
            pass

          print "Finished Successfully"
        except (KeyboardInterrupt, SystemExit) as e:
          print "Interrupt Issued. Exiting Program with error state: %s"%(str(e))


     if __name__ == '__main__':
         main()

程序的输出如下:

    #Threads get started correctly
    #The output also is getting processed but then towards the end, All i see are
    Active Threads: 16
    Active Threads: 16
    Active Threads: 16...

然后程序只是挂起或继续打印事件线程。然而，由于退出标志设置为 True，线程的运行方法未被执行。所以我不知道这些线程是如何保持运行或发生了什么。

编辑:我发现了问题。在上面的代码中，线程的 get 方法是阻塞的，因此无法退出。使用带超时的 get 方法就可以了。我有我在下面修改的运行方法的代码

    def run(self):
            try:
                   #Start Thread
                   printing "Starting %s..."%(self.name)
                   #Do Some processing
                   while not exit_flag:
                          try:
                                data = self.q.get(True,self.timeout)
                                print "%s processing %s"%(self.name,str(data))
                                self.q.task_done()
                          except:
                                 print "Queue Empty or Timeout Occurred. Try Again for %s"%(self.name)


                    # Exit thread
                    print "Exiting %s..."%(self.name)
             except Exception as e:
                print "Exiting %s due to Error: %s"%(self.name,str(e))

Answer 1

如果想在进程退出时强制所有线程退出，可以在线程创建前将线程的“daemon”标志设置为True。

http://docs.python.org/2/library/threading.html#threading.Thread.daemon