capture exception raised by child thread.

[Ype Kingma]

Joe Wong wrote:

> Hi,
> 
>  I have a class that created a child thread for processing, this thread
might raise an exception under some condition. On the main program that
create an object of this case, I put a try/except block trying to capture
the exception but failed. Am I doing anything wrong here?

See the modifications to your code. I hope I got all the
names right, it's been a while, but it should give you an idea
about one way how to do it.

> 
> here is the stripped version of my code:
> 
> class A:
>     def __init__(self):
>         self.thread = threading.Thread(None, self.MyThread)
>         self.thread.setDaemon(1)

It's a bit unusual for a deamon thread to end in an exception,
but that doesn't matter.

          self.caughtException = None
          self.endEvent = Event() # from the threading module iirc.
>         self.thread.start()
> 
>     def MyThread(self):
        try:
          try:
>           while 1:
>             # do something. if error:
> 
>             if error:
>                 raise exception
          except exc:
            self.caughtException = exc
            # evt. raise exc again
       finally:
         self.endEvent.set()

> 
> in my Main  program:
> 
> main()
>     a = A()
>     while 1:

>         # do something..

          # test (or wait) for the event from a here.
          if a.endEvent.isSet() and a.caughtException:
            ...

Have fun,
Ype