DNS cleanup

[Hal Murray]

The pool stuff is working.  There are probably lots of quirks/bugs, but the 
general structure seems right.

I did the pool stuff first because I found the code I needed while I was 
cleaning out the old stuff.  Normal host mode shouldn't be too hard.


esr at thyrsus.com said:
> Be aware that at some point I would still be interested in replacing our
> internal async-lookup code with calls to c_ares or equivalent, on the
> general principle that it's better when specialty code unrelated to our
> business logic is somebody else's maintainance problem. 

One possible reason to use something else is to get the TTL from the 
response.  There is no way to get that with the normal API.

Other than that, I'll be real surprised if you want to drag in another 
dependency.

I think you said that c_ares uses a callback.  To fit that into the 
current/new structure, all we have to do is have the called-back routine save 
or copy the data, then send a signal to the main thread.  The main thread 
will then call in to do the real callbacks in the right context.



-- 
These are my opinions.  I hate spam.