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。请考虑以下情况:
-
线程正在保存一个必须正确关闭的关键资源
-
该线程已经创建了几个其他线程,这些线程也必须被终止。
如果您负担得起(如果您管理自己的线程),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这个标志,看是否是时候让它退出了。
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):
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()
在这段代码中,您应该在希望线程退出时对其调用stop(),并使用join()等待线程正确退出。线程应定期检查停止标志。
但也有一些情况下,你真的需要杀死一个线程。一个例子是,当您包装一个外部库时,该库正忙着长时间的调用,并且您想中断它。
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
Killable Threads
托默·菲利巴。关于
PyThreadState_SetAsyncExc
似乎来自
old version of Python
)
如文档中所述,这不是一个神奇的项目符号,因为如果线程在python解释器之外很忙,它将不会捕捉到中断。
这段代码的一个好的使用模式是让线程捕获一个特定的异常并执行清理。这样,你可以中断一个任务,仍然有适当的清理。
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1 楼
