[issue13812] multiprocessing package doesn't flush stderr on child exception

[Memeplex]

Memeplex added the comment:

I would like to reopen this issue because of the following, very related, behavior. Try this:

```
import multiprocessing as mp
import time


def g():
    time.sleep(100)

def f():
    mp.Process(target=g).start()
    1/0

mp.Process(target=f).start()
```

It won't show the ZeroDivisionError until you keyboard interrupt the g() process or wait for it to end. This is because _exit_function will join every active non-daemon child, which happens before printing and flushing the error. IMO the exception should be shown before joining children, since keeping the error silent is asking for trouble.

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nosy: +memeplex

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue13812>
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