类属性没有得到正确分配

Question

我试图循环报警（文件beep.wav中），并显示一个警告。

一旦警报被关闭，我想立即停止报警。

我试图它使用的线程控制报警的播放的解决方案。

然而，它抛出一个错误：

Traceback (most recent call last): 
    File "test.py", line 28, in <module> 
    thread.stop() 
    File "test.py", line 21, in stop 
    self.process.kill() 
AttributeError: 'AlarmThread' object has no attribute 'process' 

我真的不知道为什么这个错误会抛出，但它看起来像self.process是，由于某些原因，当AlarmThread.stop被称为未分配。

这是没有意义的我，从我的代码看起来thread.stop是thread.start后只叫：

import subprocess 
import threading 

class AlarmThread(threading.Thread): 
    def __init__(self, file_name="beep.wav"): 
     super(AlarmThread, self).__init__() 
     self.file_name = file_name 
     self.ongoing = None 

    def run(self): 
     self.ongoing = True 
     while self.ongoing: 
      self.process = subprocess.Popen(["afplay", self.file_name]) 
      self.process.wait() 

    def stop(self): 
     if self.ongoing is not None: 
      self.ongoing = False 
      self.process.kill() 

thread = AlarmThread() 
thread.start() 
# show_alert is synchronous, an alert must be closed before the script continues 
show_alert("1 second timer") 

thread.stop() 
thread.join() 

Answer 1

你有一个竞争条件。该线程没有时间启动，创建该进程并在您拨打thread.stop()时分配self.process。你可以在__init__初始化self.process并用它来确定进程是否真的有

import subprocess 
import threading 

class AlarmThread(threading.Thread): 
    def __init__(self, file_name="beep.wav"): 
     super(AlarmThread, self).__init__() 
     self.lock = threading.Lock() 
     self.file_name = file_name 
     self.ongoing = False 
     self.process = None 

    def run(self): 
     self.ongoing = True 
     while True: 
      with self.lock: 
       if not self.ongoing: 
        break 
       self.process = subprocess.Popen(["afplayer", self.file_name]) 
      self.process.wait() 

    def stop(self): 
     with self.lock: 
      if self.ongoing: 
       self.ongoing = False 
       if self.process: 
        self.process.kill() 


thread = AlarmThread() 
thread.start() 
# show_alert is synchronous, an alert must be closed before the script continues 
show_alert("1 second timer") 

thread.stop() 
thread.join() 

Answer 2

是的，这是由竞争条件引起的。

The thread hasn't had time to start, create the process and assign self.process by the time you call thread.stop()

然而，我发现，在简单地等待，直到thread.process被分配依赖修复：

thread = AlarmThread() 
thread.start() 
while not thread.process: 
    time.sleep(0.1) 

show_alert(message) 

thread.stop() 
thread.join() 

我班也略有改变，以确保thread.process始终分配：

class AlarmThread(threading.Thread): 
    def __init__(self, file_name="beep.wav"): 
     super(AlarmThread, self).__init__() 
     self.file_name = file_name 
     self.ongoing = None 
     self.process = None 

    def run(self): 
     self.ongoing = True 
     while self.ongoing: 
      self.process = subprocess.Popen(["afplay", self.file_name]) 
      self.process.wait() 
      self.process = None 

    def stop(self): 
     if self.ongoing is not None: 
      self.ongoing = False 
      self.process.kill()