我对Python和多线程编程非常陌生。基本上,我有一个脚本,将文件复制到另一个位置。我想把这个放在另一个线程,这样我就可以输出....表示脚本仍在运行。

我遇到的问题是,如果文件不能复制,它将抛出异常。如果在主线程中运行,这是可以的;但是,使用以下代码是无效的:

try:
    threadClass = TheThread(param1, param2, etc.)
    threadClass.start()   ##### **Exception takes place here**
except:
    print "Caught an exception"

在线程类本身中,我试图重新抛出异常,但它不起作用。我在这里看到有人问类似的问题,但他们似乎都在做一些比我试图做的更具体的事情(我不太理解所提供的解决方案)。我看到有人提到sys.exc_info()的用法,但我不知道在哪里或如何使用它。

编辑:线程类的代码如下:

class TheThread(threading.Thread):
    def __init__(self, sourceFolder, destFolder):
        threading.Thread.__init__(self)
        self.sourceFolder = sourceFolder
        self.destFolder = destFolder
    
    def run(self):
        try:
           shul.copytree(self.sourceFolder, self.destFolder)
        except:
           raise

当前回答

作为线程的新手,我花了很长时间来理解如何实现Mateusz Kobos的代码(如上)。这里有一个明确的版本,以帮助您了解如何使用它。

#!/usr/bin/env python

import sys
import threading
import Queue

class ExThread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.__status_queue = Queue.Queue()

    def run_with_exception(self):
        """This method should be overriden."""
        raise NotImplementedError

    def run(self):
        """This method should NOT be overriden."""
        try:
            self.run_with_exception()
        except Exception:
            self.__status_queue.put(sys.exc_info())
        self.__status_queue.put(None)

    def wait_for_exc_info(self):
        return self.__status_queue.get()

    def join_with_exception(self):
        ex_info = self.wait_for_exc_info()
        if ex_info is None:
            return
        else:
            raise ex_info[1]

class MyException(Exception):
    pass

class MyThread(ExThread):
    def __init__(self):
        ExThread.__init__(self)

    # This overrides the "run_with_exception" from class "ExThread"
    # Note, this is where the actual thread to be run lives. The thread
    # to be run could also call a method or be passed in as an object
    def run_with_exception(self):
        # Code will function until the int
        print "sleeping 5 seconds"
        import time
        for i in 1, 2, 3, 4, 5:
            print i
            time.sleep(1) 
        # Thread should break here
        int("str")
# I'm honestly not sure why these appear here? So, I removed them. 
# Perhaps Mateusz can clarify?        
#         thread_name = threading.current_thread().name
#         raise MyException("An error in thread '{}'.".format(thread_name))

if __name__ == '__main__':
    # The code lives in MyThread in this example. So creating the MyThread 
    # object set the code to be run (but does not start it yet)
    t = MyThread()
    # This actually starts the thread
    t.start()
    print
    print ("Notice 't.start()' is considered to have completed, although" 
           " the countdown continues in its new thread. So you code "
           "can tinue into new processing.")
    # Now that the thread is running, the join allows for monitoring of it
    try:
        t.join_with_exception()
    # should be able to be replace "Exception" with specific error (untested)
    except Exception, e: 
        print
        print "Exceptioon was caught and control passed back to the main thread"
        print "Do some handling here...or raise a custom exception "
        thread_name = threading.current_thread().name
        e = ("Caught a MyException in thread: '" + 
             str(thread_name) + 
             "' [" + str(e) + "]")
        raise Exception(e) # Or custom class of exception, such as MyException

其他回答

问题是thread_obj.start()立即返回。您所生成的子线程在它自己的上下文中使用自己的堆栈执行。在那里发生的任何异常都在子线程的上下文中,并且在它自己的堆栈中。我现在能想到的一种将此信息传递给父线程的方法是使用某种消息传递,因此您可以研究一下。

试试这个尺寸:

import sys
import threading
import queue


class ExcThread(threading.Thread):

    def __init__(self, bucket):
        threading.Thread.__init__(self)
        self.bucket = bucket

    def run(self):
        try:
            raise Exception('An error occured here.')
        except Exception:
            self.bucket.put(sys.exc_info())


def main():
    bucket = queue.Queue()
    thread_obj = ExcThread(bucket)
    thread_obj.start()

    while True:
        try:
            exc = bucket.get(block=False)
        except queue.Empty:
            pass
        else:
            exc_type, exc_obj, exc_trace = exc
            # deal with the exception
            print exc_type, exc_obj
            print exc_trace

        thread_obj.join(0.1)
        if thread_obj.isAlive():
            continue
        else:
            break


if __name__ == '__main__':
    main()

concurrent.futures.as_completed

https://docs.python.org/3.7/library/concurrent.futures.html#concurrent.futures.as_completed

解决方案如下:

当调用异常时,立即返回主线程 不需要额外的用户定义类,因为它不需要: 显式队列 在工作线程周围添加except else

来源:

#!/usr/bin/env python3

import concurrent.futures
import time

def func_that_raises(do_raise):
    for i in range(3):
        print(i)
        time.sleep(0.1)
    if do_raise:
        raise Exception()
    for i in range(3):
        print(i)
        time.sleep(0.1)
    
with concurrent.futures.ThreadPoolExecutor(max_workers=2) as executor:
    futures = []
    futures.append(executor.submit(func_that_raises, False))
    futures.append(executor.submit(func_that_raises, True))
    for future in concurrent.futures.as_completed(futures):
        print(repr(future.exception()))

可能的输出:

0
0
1
1
2
2
0
Exception()
1
2
None

不幸的是,当一个期货失效时,不可能通过终止期货来取消其他期货:

concurrent.futures;Python:并发。如何使其可取消? 线程:有办法杀死一个线程吗? C pthreads:在Pthread库中杀死线程

如果你这样做:

for future in concurrent.futures.as_completed(futures):
    if future.exception() is not None:
        raise future.exception()

然后with语句捕获它,等待第二个线程完成,然后继续。以下行为类似:

for future in concurrent.futures.as_completed(futures):
    future.result()

因为future.result()在发生异常时重新引发异常。

如果你想退出整个Python进程,你可以使用os._exit(0),但这可能意味着你需要重构。

具有完美异常语义的自定义类

我最终为自己编写了一个完美的接口:限制一次运行的最大线程数的正确方法?部分“错误处理的队列示例”。该类的目标是既方便,又让您完全控制提交和结果/错误处理。

在Python 3.6.7, Ubuntu 18.04上测试。

类似于RickardSjogren的方法,没有Queue, sys等,但也没有一些信号监听器:直接执行一个异常处理程序,对应于一个异常块。

#!/usr/bin/env python3

import threading

class ExceptionThread(threading.Thread):

    def __init__(self, callback=None, *args, **kwargs):
        """
        Redirect exceptions of thread to an exception handler.

        :param callback: function to handle occured exception
        :type callback: function(thread, exception)
        :param args: arguments for threading.Thread()
        :type args: tuple
        :param kwargs: keyword arguments for threading.Thread()
        :type kwargs: dict
        """
        self._callback = callback
        super().__init__(*args, **kwargs)

    def run(self):
        try:
            if self._target:
                self._target(*self._args, **self._kwargs)
        except BaseException as e:
            if self._callback is None:
                raise e
            else:
                self._callback(self, e)
        finally:
            # Avoid a refcycle if the thread is running a function with
            # an argument that has a member that points to the thread.
            del self._target, self._args, self._kwargs, self._callback

只有自我。_callback和run()中的except块是普通threading.Thread之外的。

我喜欢这门课:

https://gist.github.com/earonesty/b88d60cb256b71443e42c4f1d949163e

import threading
from typing import Any


class PropagatingThread(threading.Thread):
    """A Threading Class that raises errors it caught, and returns the return value of the target on join."""

    def __init__(self, *args, **kwargs):
        self._target = None
        self._args = ()
        self._kwargs = {}
        super().__init__(*args, **kwargs)
        self.exception = None
        self.return_value = None
        assert self._target

    def run(self):
        """Don't override this if you want the behavior of this class, use target instead."""
        try:
            if self._target:
                self.return_value = self._target(*self._args, **self._kwargs)
        except Exception as e:
            self.exception = e
        finally:
            # see super().run() for why this is necessary
            del self._target, self._args, self._kwargs

    def join(self, timeout=None) -> Any:
        super().join(timeout)
        if self.exception:
            raise self.exception
        return self.return_value

我使用这个版本,它是最小的,它工作得很好。

class SafeThread(threading.Thread):
    def __init__(self, *args, **kwargs):
        super(SafeThread, self).__init__(*args, **kwargs)
        self.exception = None

    def run(self) -> None:
        try:
            super(SafeThread, self).run()
        except Exception as ex:
            self.exception = ex
            traceback.print_exc()

    def join(self, *args, **kwargs) -> None:
        super(SafeThread, self).join(*args, **kwargs)
        if self.exception:
            raise self.exception

要使用它,只需替换线程。带安全线程的线程

t = SafeThread(target = some_function, args = (some, args,))
t.start()
# do something else here if you want as the thread runs in the background
t.join()