This module contains a DNS resolver using the c-ares library (and its wrapper pycares).

class tornado.platform.caresresolver.CaresResolver

Name resolver based on the c-ares library.

This is a non-blocking and non-threaded resolver. It may not produce the same results as the system resolver, but can be used for non-blocking resolution when threads cannot be used.

c-ares fails to resolve some names when family is AF_UNSPEC, so it is only recommended for use in AF_INET (i.e. IPv4). This is the default for tornado.simple_httpclient, but other libraries may default to AF_UNSPEC.