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
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()
这个问题有很多非常奇怪复杂的答案。我是不是把它简化了,因为对我来说,这似乎对大多数事情都足够了。
from threading import Thread
class PropagatingThread(Thread):
def run(self):
self.exc = None
try:
if hasattr(self, '_Thread__target'):
# Thread uses name mangling prior to Python 3.
self.ret = self._Thread__target(*self._Thread__args, **self._Thread__kwargs)
else:
self.ret = self._target(*self._args, **self._kwargs)
except BaseException as e:
self.exc = e
def join(self, timeout=None):
super(PropagatingThread, self).join(timeout)
if self.exc:
raise self.exc
return self.ret
如果你确定你只会在一个或另一个版本的Python上运行,你可以将run()方法减少到只有被破坏的版本(如果你只在3之前的Python版本上运行),或者仅仅是干净的版本(如果你只在3开始的Python版本上运行)。
使用示例:
def f(*args, **kwargs):
print(args)
print(kwargs)
raise Exception('I suck at this')
t = PropagatingThread(target=f, args=(5,), kwargs={'hello':'world'})
t.start()
t.join()
当您加入时,您将看到在另一个线程上引发异常。
如果您正在使用six或仅在Python 3上使用,则可以改进重新引发异常时获得的堆栈跟踪信息。您可以将内部异常包装在一个新的外部异常中,而不是仅在连接点处使用堆栈,并使用
six.raise_from(RuntimeError('Exception in thread'),self.exc)
or
raise RuntimeError('Exception in thread') from self.exc
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
Pygolang提供同步功能。工作组,特别是将异常从派生的工作线程传播到主线程。例如:
#!/usr/bin/env python
"""This program demostrates how with sync.WorkGroup an exception raised in
spawned thread is propagated into main thread which spawned the worker."""
from __future__ import print_function
from golang import sync, context
def T1(ctx, *argv):
print('T1: run ... %r' % (argv,))
raise RuntimeError('T1: problem')
def T2(ctx):
print('T2: ran ok')
def main():
wg = sync.WorkGroup(context.background())
wg.go(T1, [1,2,3])
wg.go(T2)
try:
wg.wait()
except Exception as e:
print('Tmain: caught exception: %r\n' %e)
# reraising to see full traceback
raise
if __name__ == '__main__':
main()
在运行时给出以下结果:
T1: run ... ([1, 2, 3],)
T2: ran ok
Tmain: caught exception: RuntimeError('T1: problem',)
Traceback (most recent call last):
File "./x.py", line 28, in <module>
main()
File "./x.py", line 21, in main
wg.wait()
File "golang/_sync.pyx", line 198, in golang._sync.PyWorkGroup.wait
pyerr_reraise(pyerr)
File "golang/_sync.pyx", line 178, in golang._sync.PyWorkGroup.go.pyrunf
f(pywg._pyctx, *argv, **kw)
File "./x.py", line 10, in T1
raise RuntimeError('T1: problem')
RuntimeError: T1: problem
问题的原始代码将是:
wg = sync.WorkGroup(context.background())
def _(ctx):
shul.copytree(sourceFolder, destFolder)
wg.go(_)
# waits for spawned worker to complete and, on error, reraises
# its exception on the main thread.
wg.wait()
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。
我认为其他的解决方案有点复杂,如果你唯一想要的是真正看到某个异常,而不是完全无视和盲目。
解决方案是创建一个自定义线程,从主线程获取记录器并记录任何异常。
class ThreadWithLoggedException(threading.Thread):
"""
Similar to Thread but will log exceptions to passed logger.
Args:
logger: Logger instance used to log any exception in child thread
Exception is also reachable via <thread>.exception from the main thread.
"""
def __init__(self, *args, **kwargs):
try:
self.logger = kwargs.pop("logger")
except KeyError:
raise Exception("Missing 'logger' in kwargs")
super().__init__(*args, **kwargs)
self.exception = None
def run(self):
try:
if self._target is not None:
self._target(*self._args, **self._kwargs)
except Exception as exception:
thread = threading.current_thread()
self.exception = exception
self.logger.exception(f"Exception in child thread {thread}: {exception}")
finally:
del self._target, self._args, self._kwargs
例子:
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
logger.addHandler(logging.StreamHandler())
def serve():
raise Exception("Earth exploded.")
th = ThreadWithLoggedException(target=serve, logger=logger)
th.start()
主线程输出:
Exception in child thread <ThreadWithLoggedException(Thread-1, started 139922384414464)>: Earth exploded.
Traceback (most recent call last):
File "/core/utils.py", line 108, in run
self._target(*self._args, **self._kwargs)
File "/myapp.py", line 105, in serve
raise Exception("Earth exploded.")
Exception: Earth exploded.