No need for a separate variable ndns.
The memory leak detection will detect code that fails to release a dns reference.
The DEBUGASSERT will detect code that releases too many references.
(http://curl.haxx.se/bug/view.cgi?id=2891595) which identified how an entry
in the DNS cache would linger too long if the request that added it was in
use that long. He also provided the patch that now makes libcurl capable of
still doing a request while the DNS hash entry may get timed out.
libcurl to resolve 'localhost' whatever name you use in the URL *if* you set
the --interface option to (exactly) "LocalHost". This will enable us to
write tests for custom hosts names but still use a local host server.
(http://curl.haxx.se/bug/view.cgi?id=1911069) that identified a race
condition in the name resolver code when the DNS cache is shared between
multiple easy handles, each running in simultaneous threads that could cause
crashes.
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.
hash function for different hashes, and also expanded the default size for
the socket hash table used in multi handles to greatly enhance speed when
very many connections are added and the socket API is used.
the crash was that libcurl internally was a bit confused about who owned the
DNS cache at all times so if you created an easy handle that uses a shared
DNS cache and added that to a multi handle it would crash. Now we keep more
careful internal track of exactly what kind of DNS cache each easy handle
uses: None, Private (allocated for and used only by this single handle),
Shared (points to a cache held by a shared object), Global (points to the
global cache) or Multi (points to the cache within the multi handle that is
automatically shared between all easy handles that are added with private
caches).
