类属性未正确分配

Question

我正在尝试循环警报（在文件 beep.wav 中）并显示警报。

警报关闭后，我想立即停止警报。

我正在尝试使用线程控制警报播放的解决方案。

但是，它会引发错误：

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会抛出这个错误，但看起来 self.process 出于某种原因在调用 AlarmThread.stop 时没有分配。

这对我来说毫无意义，因为从我的代码看来 thread.stop 仅在 thread.start 之后被调用：

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。线程没有时间启动，创建进程并在您调用thread.stop() 时分配self.process。您可以在 __init__ 中初始化 self.process 并使用它来查看进程是否真的存在

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，它是由竞争条件引起的。

线程还没来得及启动，创建进程并在你调用thread.stop()时分配self.process

但是，我发现了一个修复方法，它依赖于等待分配 thread.process：

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

show_alert(message)

thread.stop()
thread.join()

我的班级也略有改变，以确保始终分配thread.process：

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()