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()
我做的是，简单的覆盖连接和运行线程的方法:
class RaisingThread(threading.Thread):
def run(self):
self._exc = None
try:
super().run()
except Exception as e:
self._exc = e
def join(self, timeout=None):
super().join(timeout=timeout)
if self._exc:
raise self._exc
用途如下:
def foo():
time.sleep(2)
print('hi, from foo!')
raise Exception('exception from foo')
t = RaisingThread(target=foo)
t.start()
try:
t.join()
except Exception as e:
print(e)
结果:
hi, from foo!
exception from foo!
捕获线程异常并与调用方方法通信的一个简单方法是将字典或列表传递给worker方法。
示例(将字典传递给工作方法):
import threading
def my_method(throw_me):
raise Exception(throw_me)
def worker(shared_obj, *args, **kwargs):
try:
shared_obj['target'](*args, **kwargs)
except Exception as err:
shared_obj['err'] = err
shared_obj = {'err':'', 'target': my_method}
throw_me = "Test"
th = threading.Thread(target=worker, args=(shared_obj, throw_me), kwargs={})
th.start()
th.join()
if shared_obj['err']:
print(">>%s" % shared_obj['err'])
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。
我喜欢的一种方法是基于观察者模式。我定义了一个信号类，线程用它向侦听器发出异常。它还可以用于从线程返回值。例子:
import threading
class Signal:
def __init__(self):
self._subscribers = list()
def emit(self, *args, **kwargs):
for func in self._subscribers:
func(*args, **kwargs)
def connect(self, func):
self._subscribers.append(func)
def disconnect(self, func):
try:
self._subscribers.remove(func)
except ValueError:
raise ValueError('Function {0} not removed from {1}'.format(func, self))
class WorkerThread(threading.Thread):
def __init__(self, *args, **kwargs):
super(WorkerThread, self).__init__(*args, **kwargs)
self.Exception = Signal()
self.Result = Signal()
def run(self):
if self._Thread__target is not None:
try:
self._return_value = self._Thread__target(*self._Thread__args, **self._Thread__kwargs)
except Exception as e:
self.Exception.emit(e)
else:
self.Result.emit(self._return_value)
if __name__ == '__main__':
import time
def handle_exception(exc):
print exc.message
def handle_result(res):
print res
def a():
time.sleep(1)
raise IOError('a failed')
def b():
time.sleep(2)
return 'b returns'
t = WorkerThread(target=a)
t2 = WorkerThread(target=b)
t.Exception.connect(handle_exception)
t2.Result.connect(handle_result)
t.start()
t2.start()
print 'Threads started'
t.join()
t2.join()
print 'Done'
我没有足够的使用线程的经验来断言这是一种完全安全的方法。但这对我来说很管用，我喜欢这种灵活性。
