是否有可能终止一个正在运行的线程而不设置/检查任何标志/信号/等等?


当前回答

使用setDaemon(True)启动子线程。

def bootstrap(_filename):
    mb = ModelBootstrap(filename=_filename) # Has many Daemon threads. All get stopped automatically when main thread is stopped.

t = threading.Thread(target=bootstrap,args=('models.conf',))
t.setDaemon(False)

while True:
    t.start()
    time.sleep(10) # I am just allowing the sub-thread to run for 10 sec. You can listen on an event to stop execution.
    print('Thread stopped')
    break

其他回答

最简单的方法是:

from threading import Thread
from time import sleep

def do_something():
    global thread_work
    while thread_work:
        print('doing something')
        sleep(5)
    print('Thread stopped')

thread_work = True
Thread(target=do_something).start()
sleep(5)
thread_work = False

你不应该在没有与线程合作的情况下强行终止线程。

杀死一个线程消除了try/finally阻塞设置的任何保证,所以你可能会让锁锁定,文件打开等等。

唯一可以认为强制终止线程是一个好主意的情况是快速终止程序,但绝不是单个线程。

假设,你想有多个线程的同一个函数,这是IMHO最简单的实现通过id停止一个:

import time
from threading import Thread

def doit(id=0):
    doit.stop=0
    print("start id:%d"%id)
    while 1:
        time.sleep(1)
        print(".")
        if doit.stop==id:
            doit.stop=0
            break
    print("end thread %d"%id)

t5=Thread(target=doit, args=(5,))
t6=Thread(target=doit, args=(6,))

t5.start() ; t6.start()
time.sleep(2)
doit.stop =5  #kill t5
time.sleep(2)
doit.stop =6  #kill t6

这里的好处是,你可以有多个相同或不同的函数,并通过functionname。stop来停止它们

如果你想只有一个线程的函数,那么你不需要记住id。如果做了,就停下来。停止> 0。

多处理。进程可以p.terminate()

如果我想杀死一个线程,但不想使用标志/锁/信号/信号量/事件/任何东西,我就把线程提升到完整的进程。对于只使用几个线程的代码,开销并没有那么糟糕。

例如,这可以方便地终止执行阻塞I/O的助手“线程”

转换很简单:在相关代码中替换所有线程。多线程线程。进程和所有队列。多处理队列。排队并将p.t terminate()所需的调用添加到想要杀死子进程p的父进程中

关于多处理,请参阅Python文档。

例子:

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

在Python和任何语言中,突然终止线程通常都是一种糟糕的模式。考虑以下情况:

线程持有一个必须正确关闭的关键资源 线程创建了其他几个线程,这些线程也必须被杀死。

如果你能负担得起(如果你在管理自己的线程),处理这个问题的好方法是有一个exit_request标志,每个线程都会定期检查它,看看它是否到了退出的时候。

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()

在这段代码中,当您希望线程退出时,应该在线程上调用stop(),并使用join()等待线程正确退出。线程应该定期检查停止标志。

然而,在某些情况下,您确实需要终止一个线程。例如,当您正在包装一个外部库时,该库正忙于长时间的调用,并且您希望中断它。

下面的代码允许(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 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 )

(根据Tomer Filiba的《Killable Threads》改编。关于PyThreadState_SetAsyncExc返回值的引用似乎来自旧版本的Python。)

正如文档中所指出的,这不是一个神奇的子弹,因为如果线程在Python解释器之外忙,它将不会捕获中断。

这段代码的一个良好使用模式是让线程捕获特定的异常并执行清理。这样,您可以中断任务,但仍然可以进行适当的清理。