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

如果您试图终止整个程序,您可以将线程设置为“守护进程”。看到 Thread.daemon

其他回答

实现一个线程是绝对可能的。方法,如下例代码所示:

import sys
import threading
import time


class StopThread(StopIteration):
    pass

threading.SystemExit = SystemExit, StopThread


class Thread2(threading.Thread):

    def stop(self):
        self.__stop = True

    def _bootstrap(self):
        if threading._trace_hook is not None:
            raise ValueError('Cannot run thread with tracing!')
        self.__stop = False
        sys.settrace(self.__trace)
        super()._bootstrap()

    def __trace(self, frame, event, arg):
        if self.__stop:
            raise StopThread()
        return self.__trace


class Thread3(threading.Thread):

    def _bootstrap(self, stop_thread=False):
        def stop():
            nonlocal stop_thread
            stop_thread = True
        self.stop = stop

        def tracer(*_):
            if stop_thread:
                raise StopThread()
            return tracer
        sys.settrace(tracer)
        super()._bootstrap()

###############################################################################


def main():
    test1 = Thread2(target=printer)
    test1.start()
    time.sleep(1)
    test1.stop()
    test1.join()
    test2 = Thread2(target=speed_test)
    test2.start()
    time.sleep(1)
    test2.stop()
    test2.join()
    test3 = Thread3(target=speed_test)
    test3.start()
    time.sleep(1)
    test3.stop()
    test3.join()


def printer():
    while True:
        print(time.time() % 1)
        time.sleep(0.1)


def speed_test(count=0):
    try:
        while True:
            count += 1
    except StopThread:
        print('Count =', count)

if __name__ == '__main__':
    main()

Thread3类运行代码的速度似乎比Thread2类快大约33%。

正如其他人所提到的,规范是设置一个停止标志。对于一些轻量级的东西(没有Thread的子类化,没有全局变量),lambda回调是一个选项。(注意if stop()中的括号。)

import threading
import time

def do_work(id, stop):
    print("I am thread", id)
    while True:
        print("I am thread {} doing something".format(id))
        if stop():
            print("  Exiting loop.")
            break
    print("Thread {}, signing off".format(id))


def main():
    stop_threads = False
    workers = []
    for id in range(0,3):
        tmp = threading.Thread(target=do_work, args=(id, lambda: stop_threads))
        workers.append(tmp)
        tmp.start()
    time.sleep(3)
    print('main: done sleeping; time to stop the threads.')
    stop_threads = True
    for worker in workers:
        worker.join()
    print('Finis.')

if __name__ == '__main__':
    main()

将print()替换为始终刷新的pr()函数(sys.stdout.flush())可以提高shell输出的精度。

(仅在Windows/Eclipse/Python3.3上测试)

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

虽然它相当古老,但对一些人来说这可能是一个方便的解决方案:

一个扩展线程模块功能的小模块—— 允许一个线程在另一个线程的上下文中引发异常 线程。通过触发SystemExit,你最终可以杀死python线程。

import threading
import ctypes     

def _async_raise(tid, excobj):
    res = ctypes.pythonapi.PyThreadState_SetAsyncExc(tid, ctypes.py_object(excobj))
    if res == 0:
        raise ValueError("nonexistent 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(tid, 0)
        raise SystemError("PyThreadState_SetAsyncExc failed")

class Thread(threading.Thread):
    def raise_exc(self, excobj):
        assert self.isAlive(), "thread must be started"
        for tid, tobj in threading._active.items():
            if tobj is self:
                _async_raise(tid, excobj)
                return

        # the thread was alive when we entered the loop, but was not found 
        # in the dict, hence it must have been already terminated. should we raise
        # an exception here? silently ignore?

    def terminate(self):
        # must raise the SystemExit type, instead of a SystemExit() instance
        # due to a bug in PyThreadState_SetAsyncExc
        self.raise_exc(SystemExit)

因此,它允许“线程在另一个线程的上下文中引发异常”,通过这种方式,被终止的线程可以处理终止,而无需定期检查中止标志。

然而,根据其原始来源,这段代码有一些问题。

The exception will be raised only when executing python bytecode. If your thread calls a native/built-in blocking function, the exception will be raised only when execution returns to the python code. There is also an issue if the built-in function internally calls PyErr_Clear(), which would effectively cancel your pending exception. You can try to raise it again. Only exception types can be raised safely. Exception instances are likely to cause unexpected behavior, and are thus restricted. For example: t1.raise_exc(TypeError) and not t1.raise_exc(TypeError("blah")). IMHO it's a bug, and I reported it as one. For more info, http://mail.python.org/pipermail/python-dev/2006-August/068158.html I asked to expose this function in the built-in thread module, but since ctypes has become a standard library (as of 2.5), and this feature is not likely to be implementation-agnostic, it may be kept unexposed.

Python版本:3.8

使用守护线程来执行我们想要的,如果我们想要终止守护线程,我们只需要让父线程退出,然后系统就会终止父线程创建的守护线程。

还支持协程和协程函数。

def main():
    start_time = time.perf_counter()
    t1 = ExitThread(time.sleep, (10,), debug=False)
    t1.start()
    time.sleep(0.5)
    t1.exit()
    try:
        print(t1.result_future.result())
    except concurrent.futures.CancelledError:
        pass
    end_time = time.perf_counter()
    print(f"time cost {end_time - start_time:0.2f}")

下面是ExitThread源代码

import concurrent.futures
import threading
import typing
import asyncio


class _WorkItem(object):
    """ concurrent\futures\thread.py

    """

    def __init__(self, future, fn, args, kwargs, *, debug=None):
        self._debug = debug
        self.future = future
        self.fn = fn
        self.args = args
        self.kwargs = kwargs

    def run(self):
        if self._debug:
            print("ExitThread._WorkItem run")
        if not self.future.set_running_or_notify_cancel():
            return

        try:
            coroutine = None
            if asyncio.iscoroutinefunction(self.fn):
                coroutine = self.fn(*self.args, **self.kwargs)
            elif asyncio.iscoroutine(self.fn):
                coroutine = self.fn
            if coroutine is None:
                result = self.fn(*self.args, **self.kwargs)
            else:
                result = asyncio.run(coroutine)
            if self._debug:
                print("_WorkItem done")
        except BaseException as exc:
            self.future.set_exception(exc)
            # Break a reference cycle with the exception 'exc'
            self = None
        else:
            self.future.set_result(result)


class ExitThread:
    """ Like a stoppable thread

    Using coroutine for target then exit before running may cause RuntimeWarning.

    """

    def __init__(self, target: typing.Union[typing.Coroutine, typing.Callable] = None
                 , args=(), kwargs={}, *, daemon=None, debug=None):
        #
        self._debug = debug
        self._parent_thread = threading.Thread(target=self._parent_thread_run, name="ExitThread_parent_thread"
                                               , daemon=daemon)
        self._child_daemon_thread = None
        self.result_future = concurrent.futures.Future()
        self._workItem = _WorkItem(self.result_future, target, args, kwargs, debug=debug)
        self._parent_thread_exit_lock = threading.Lock()
        self._parent_thread_exit_lock.acquire()
        self._parent_thread_exit_lock_released = False  # When done it will be True
        self._started = False
        self._exited = False
        self.result_future.add_done_callback(self._release_parent_thread_exit_lock)

    def _parent_thread_run(self):
        self._child_daemon_thread = threading.Thread(target=self._child_daemon_thread_run
                                                     , name="ExitThread_child_daemon_thread"
                                                     , daemon=True)
        self._child_daemon_thread.start()
        # Block manager thread
        self._parent_thread_exit_lock.acquire()
        self._parent_thread_exit_lock.release()
        if self._debug:
            print("ExitThread._parent_thread_run exit")

    def _release_parent_thread_exit_lock(self, _future):
        if self._debug:
            print(f"ExitThread._release_parent_thread_exit_lock {self._parent_thread_exit_lock_released} {_future}")
        if not self._parent_thread_exit_lock_released:
            self._parent_thread_exit_lock_released = True
            self._parent_thread_exit_lock.release()

    def _child_daemon_thread_run(self):
        self._workItem.run()

    def start(self):
        if self._debug:
            print(f"ExitThread.start {self._started}")
        if not self._started:
            self._started = True
            self._parent_thread.start()

    def exit(self):
        if self._debug:
            print(f"ExitThread.exit exited: {self._exited} lock_released: {self._parent_thread_exit_lock_released}")
        if self._parent_thread_exit_lock_released:
            return
        if not self._exited:
            self._exited = True
            if not self.result_future.cancel():
                if self.result_future.running():
                    self.result_future.set_exception(concurrent.futures.CancelledError())