有什么办法可以杀死线程吗? [英] Is there any way to kill a Thread?
问题描述
是否可以在不设置/检查任何标志/信号灯/等的情况下终止正在运行的线程?
Is it possible to terminate a running thread without setting/checking any flags/semaphores/etc.?
推荐答案
用Python和任何语言突然终止线程通常是一种错误的模式.考虑以下情况:
It is generally a bad pattern to kill a thread abruptly, in Python and in any language. Think of the following cases:
- 线程正在保存必须正确关闭的关键资源
- 该线程创建了其他几个必须同时终止的线程.
如果您能负担得起的话(如果您要管理自己的线程),处理此问题的一种好方法是有一个exit_request标志,每个线程定期检查一次退出时间,以查看是否该退出该线程.
The nice way of handling this if you can afford it (if you are managing your own threads) is to have an exit_request flag that each threads checks on regular interval to see if it is time for it to exit.
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,要退出线程时应在线程上调用stop()
,并使用join()
等待线程正确退出.线程应定期检查停止标志.
In this code, you should call stop()
on the thread when you want it to exit, and wait for the thread to exit properly using join()
. The thread should check the stop flag at regular intervals.
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.
There are cases however when you really need to kill a thread. An example is when you are wrapping an external library that is busy for long calls and you want to interrupt it.
以下代码允许(有一些限制)在Python线程中引发异常:
The following code allows (with some restrictions) to raise an Exception in a Python thread:
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的可杀死的线程.有关PyThreadState_SetAsyncExc
返回值的引用似乎来自 Python的旧版本.)
(Based on Killable Threads by Tomer Filiba. The quote about the return value of PyThreadState_SetAsyncExc
appears to be from an old version of Python.)
如文档中所述,这不是灵丹妙药,因为如果线程在Python解释器之外很忙,它将无法捕获中断.
As noted in the documentation, this is not a magic bullet because if the thread is busy outside the Python interpreter, it will not catch the interruption.
此代码的一个很好的用法模式是让线程捕获特定的异常并执行清理.这样,您可以中断任务并仍然进行适当的清理.
A good usage pattern of this code is to have the thread catch a specific exception and perform the cleanup. That way, you can interrupt a task and still have proper cleanup.
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