release function raises exception when file handler is already closed

[Nir Arad]

In ConcurrentRotatingFileHandler.release() you're calling:
self.stream.flush()

If the file handler is already closed, a ValueError is raised ("I/O operation on closed file").
You can wrap the code is a try block like so to avoid such problem:

    def release(self):
        """ Release file and thread locks. Flush stream and take care of closing
        stream in 'degraded' mode. """
        try:
            self.stream.flush()
            if self._rotateFailed:
                self.stream.close()
        except ValueError:
            pass # I/O operation on closed file
        finally:
            try:
                unlock(self.stream_lock)
            finally:
                # release thread lock
                logging.Handler.release(self)