def run(self):
        """
        Start the event loop.  Exit the loop when any callback raises
        an exception.  If ExitMainLoop is raised, exit cleanly.

        >>> import os
        >>> rd, wr = os.pipe()
        >>> os.write(wr, "data") # something to read from rd
        4
        >>> evl = TwistedEventLoop()
        >>> def say_hello_data():
        ...     print "hello data"
        ...     os.read(rd, 4)
        >>> def say_hello():
        ...     print "hello"
        >>> handle = evl.watch_file(rd, say_hello_data)
        >>> def say_being_twisted():
        ...     print "oh I'm messed up"
        ...     raise ExitMainLoop
        >>> handle = evl.alarm(0.0625, say_being_twisted)
        >>> handle = evl.alarm(0.03125, say_hello)
        >>> evl.run()
        hello data
        hello
        oh I'm messed up
        """
        if not self.manage_reactor:
            self.reactor.run()
        if self._exc_info:
            # An exception caused us to exit, raise it now
            exc_info = self._exc_info
            self._exc_info = None
            raise exc_info[0], exc_info[1], exc_info[2]