For me at least, raising an exception in a callback does not do anything to the request

test_tornado_async_error.py

from tornado import ioloop, web, httpserver, httpclient

PORT = 8080
            
class TestHandler(web.RequestHandler):

    @web.asynchronous
    def get(self):
        url = "http://www.google.com"
        print "fetching",url
        http = httpclient.AsyncHTTPClient()
        http.fetch(url,callback=self._test)
        
    def _test(self,response):
        print "Uploaded: now fail"
        raise web.HTTPError(500)

if __name__ == "__main__":
    print "Testing error handling of async tornado on port",PORT
    server = httpserver.HTTPServer(web.Application((
            (r"/",TestHandler),
            )))
    server.listen(PORT)
    _ioloop = ioloop.IOLoop.instance()
    _ioloop.start()