Question

我正在使用ThreadPoolExecutor执行导致错误的函数。当在线程内引起错误（并且未处理）时，似乎正在终止该线程，但未将任何内容打印到stderr或导致程序崩溃。为什么会这样？我可以这样做，以便任何线程中未处理的错误都导致整个程序崩溃吗？另外，它可以打印在某个地方，以便我可以看到发生了什么。

我注意到该错误可以在try-catch块中捕获，因此肯定会引发该错误。如果在没有线程的情况下调用相同的函数，则会按预期引发错误。

from concurrent.futures import ThreadPoolExecutor
import time


def error_causer(x):
    print(x)
    raise ValueError("This bad!")


with ThreadPoolExecutor(max_workers=1) as executor:
    executor.map(error_causer, ["coming from thread"])

print("After don't catch. Should have crashed by now...")
time.sleep(2)

error_causer("coming from outside thread")

在线程内引发ValueError时，该程序不会崩溃，但是在线程外引发ValueError时，该程序不会崩溃。

输出为：

coming from thread
After don't catch. Should have crashed by now...
coming from outside thread
Traceback (most recent call last):
  File "./another_threading_test.py", line 16, in <module>
    error_causer("coming from outside thread")
  File "./another_threading_test.py", line 7, in error_causer
    raise ValueError("This bad!")
ValueError: This bad!

我希望它在print("after don't catch")

之前崩溃

Answer 1

executor.map()不会引发错误，因为工作线程会在不引发错误的情况下以静默方式终止，除非您尝试根据docs从迭代器中检索结果：

map（func，* iterables，timeout = None，chunksize = 1）

如果函数调用引发异常，则将引发该异常   从迭代器中获取其值时。

您可以通过在返回的next()上调用iterator来验证这一点：

def error_causer(x):
    print(x)
    raise ValueError("This bad!")


with ThreadPoolExecutor(max_workers=1) as executor:
    iterator = executor.map(error_causer, ["coming from thread"])
    next(iterator)

现在，在迭代器上调用next()之后，您会看到主线程中出现了来自终止主线程的工作线程的错误：

Traceback (most recent call last):
  File "/Users/ambhowmi/PycharmProjects/Datastructures/TwoStacksQueue.py", line 13, in <module>
    next(iterator)
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/_base.py", line 598, in result_iterator
    yield fs.pop().result()
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/_base.py", line 428, in result
    return self.__get_result()
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/_base.py", line 384, in __get_result
    raise self._exception
  File "/usr/local/Cellar/python/3.7.4/Frameworks/Python.framework/Versions/3.7/lib/python3.7/concurrent/futures/thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/Users/ambhowmi/PycharmProjects/Datastructures/TwoStacksQueue.py", line 8, in error_causer
    raise ValueError("This bad!")
ValueError: This bad!

如何在Python的线程内处理错误？

1 个答案: