Re: Need cancel() on async_resolve() to callback the resolve handler immediately

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2021-08-25 10:26:53

On 8/25/21 1:23 PM, Andrey Semashev wrote:
> On 8/25/21 11:27 AM, Richard Hodges via Boost wrote:
>> There are a couple of convoluted ways to build cancellation into the 
>> linux
>> resolve() activity.
>> The problem is that the sockets and timers used for this are entirely
>> embedded in the OS-shipped library layer and not accessible to user code.
>> It's a bit of a mess that has never been cleaned up. There isn't much 
>> that
>> Asio can do about it.
>>
>> At present the "cleanest" way is to fork a child process to do the 
>> resolve
>> call for you and async_wait on a pipe from that child. If you want to
>> cancel it, send the child a SIGKILL which will result in the wait on the
>> pipe completing with an error.
>>
>> Ghastly I know...
> 
> On Linux, there is also getaddrinfo_a:
> 
> https://man7.org/linux/man-pages/man3/getaddrinfo_a.3.html
> 
> which allows to perform name resolution asynchronously, with 
> cancellation. It's a GNU extension. I wonder if it can be incorporated 
> into Boost.ASIO.

It seems, it's even been suggested before:

https://github.com/chriskohlhoff/asio/issues/449