The signalling of that a global DNS cache is wanted is done by setting the
option but the setting of the internal variable that it is in use must not be
done until it finally actually gets used!
NOTE and WARNING: I noticed that you can't actually switch off the global dns
cache with CURLOPT_DNS_USE_GLOBAL_CACHE but you couldn't do that previously
either and the option is very clearly and loudly documented as DO NOTE USE so
I won't bother to fix this bug now.
silly code left from when we switched to let the multi handle "hold" the dns
cache when using the multi interface... Of course this only triggered when a
certain function call returned error at the correct moment.
(http://curl.haxx.se/bug/view.cgi?id=1431750) helped me identify and fix two
different but related bugs:
1) Removing an easy handle from a multi handle before the transfer is done
could leave a connection in the connection cache for that handle that is
in a state that isn't suitable for re-use. A subsequent re-use could then
read from a NULL pointer and segfault.
2) When an easy handle was removed from the multi handle, there could be an
outstanding c-ares DNS name resolve request. When the response arrived,
it caused havoc since the connection struct it "belonged" to could've
been freed already.
Now Curl_done() is called when an easy handle is removed from a multi handle
pre-maturely (that is, before the transfer was complteted). Curl_done() also
makes sure to cancel all (if any) outstanding c-ares requests.
my_getaddrinfo() has been called (and wait has been set to TRUE), we check
if the name already is resolved and if so don't return wait status to the
parent. This can happen with IP-only names.
counter so that the caller needs to decrease that counter when done with
the returned data.
If compiled with MALLOCDEBUG I've added some extra checking that the counter
is decreased before a handle is closed etc.
any name resolved data in any curl handle struct. That way, we won't mind
if the cache entries are pruned for the next time we need them. We'll just
resolve them again instead.
This changes the Curl_resolv() proto. It modifies the SessionHandle struct
but perhaps most importantly, it'll make the internals somewhat dependent
on the DNS cache not being disabled as that will cripple operations somewhat.
Especially for persistant connections.
