python – 有没有办法杀死一个线程？

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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？

解决方法:

在Python和任何语言中突然杀死一个线程通常是一种糟糕的模式.想想以下情况：

>线程持有必须正确关闭的关键资源
>线程已经创建了几个必须被杀死的其他线程.

如果你负担得起它(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,每个线程定期检查它是否有时间退出.

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):
        super(StoppableThread, self).__init__()
        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,您应该在线程上调用stop(),并等待线程使用join()正确退出.线程应定期检查停止标志.

但是有些情况下你真的需要杀死一个线程.例如,当您包装一个忙于长时间调用的外部库并且您想要中断它时.

以下代码允许(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 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 excpetion 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PyThreadState_SetAsyncExc的返回值的引用似乎来自old version of Python.)

如文档中所述,这不是一个神奇的子弹,因为如果线程在Python解释器之外繁忙,它将不会捕获中断.

此代码的良好使用模式是让线程捕获特定异常并执行清理.这样,您可以中断任务并仍然进行适当的清理.

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