有没有办法杀死线程?

2022-09-05 01:13:21

是否可以在不设置/检查任何标志/信号量/等的情况下终止正在运行的线程?


答案 1

在Python和任何语言中突然杀死线程通常是一种不好的模式。请考虑以下情况:

  • 线程正在保存必须正确关闭的关键资源
  • 该线程还创建了其他几个必须杀死的线程。

如果你能负担得起(如果你正在管理自己的线程),处理这个问题的好方法是有一个exit_request标志,每个线程定期检查一次,看看它是否是时候退出了。

例如:

import threading

class StoppableThread(threading.Thread):
    """Thread class with a stop() method. The thread itself has to check
    regularly for the stopped() condition."""

    def __init__(self,  *args, **kwargs):
        super(StoppableThread, self).__init__(*args, **kwargs)
        self._stop_event = threading.Event()

    def stop(self):
        self._stop_event.set()

    def stopped(self):
        return self._stop_event.is_set()

在此代码中,应在希望线程退出时调用该线程,并使用 等待线程正确退出。线程应定期检查停止标志。stop()join()

但是,在某些情况下,您确实需要杀死线程。例如,当您包装一个忙于长时间调用的外部库,并且想要中断它时。

以下代码允许(但有一些限制)在 Python 线程中引发异常:

def _async_raise(tid, exctype):
    '''Raises an exception in the threads with id tid'''
    if not inspect.isclass(exctype):
        raise TypeError("Only types can be raised (not instances)")
    res = ctypes.pythonapi.PyThreadState_SetAsyncExc(ctypes.c_long(tid),
                                                     ctypes.py_object(exctype))
    if res == 0:
        raise ValueError("invalid thread id")
    elif res != 1:
        # "if it returns a number greater than one, you're in trouble,
        # and you should call it again with exc=NULL to revert the effect"
        ctypes.pythonapi.PyThreadState_SetAsyncExc(ctypes.c_long(tid), None)
        raise SystemError("PyThreadState_SetAsyncExc failed")

class ThreadWithExc(threading.Thread):
    '''A thread class that supports raising an exception in the thread from
       another thread.
    '''
    def _get_my_tid(self):
        """determines this (self's) thread id

        CAREFUL: this function is executed in the context of the caller
        thread, to get the identity of the thread represented by this
        instance.
        """
        if not self.isAlive():
            raise threading.ThreadError("the thread is not active")

        # do we have it cached?
        if hasattr(self, "_thread_id"):
            return self._thread_id

        # no, look for it in the _active dict
        for tid, tobj in threading._active.items():
            if tobj is self:
                self._thread_id = tid
                return tid

        # TODO: in python 2.6, there's a simpler way to do: self.ident

        raise AssertionError("could not determine the thread's id")

    def raiseExc(self, exctype):
        """Raises the given exception type in the context of this thread.

        If the thread is busy in a system call (time.sleep(),
        socket.accept(), ...), the exception is simply ignored.

        If you are sure that your exception should terminate the thread,
        one way to ensure that it works is:

            t = ThreadWithExc( ... )
            ...
            t.raiseExc( SomeException )
            while t.isAlive():
                time.sleep( 0.1 )
                t.raiseExc( SomeException )

        If the exception is to be caught by the thread, you need a way to
        check that your thread has caught it.

        CAREFUL: this function is executed in the context of the
        caller thread, to raise an exception in the context of the
        thread represented by this instance.
        """
        _async_raise( self._get_my_tid(), exctype )

(基于Tomer Filiba的Killable Threads。关于 返回值的引用似乎来自旧版本的 PythonPyThreadState_SetAsyncExc

如文档中所述,这不是一个灵丹妙药,因为如果线程在Python解释器外部繁忙,它将不会捕获中断。

此代码的一个很好的使用模式是让线程捕获特定异常并执行清理。这样,您可以中断任务,并且仍然可以进行适当的清理。


答案 2

多处理。进程可以 p.terminate()

在我想杀死一个线程,但不想使用标志/锁/信号量/事件/任何东西的情况下,我将线程提升到完整的进程。对于仅使用几个线程的代码,开销并不是那么糟糕。

例如,这可以方便地终止执行阻塞I / O的帮助程序“线程”

转换是微不足道的:在相关代码中,将 all 替换为 和 all 替换为,并将 所需的调用添加到想要杀死其子进程的父进程threading.Threadmultiprocessing.Processqueue.Queuemultiprocessing.Queuep.terminate()p

请参阅有关多处理的 Python 文档

例:

import multiprocessing
proc = multiprocessing.Process(target=your_proc_function, args=())
proc.start()
# Terminate the process
proc.terminate()  # sends a SIGTERM