Looking at the code of Curl_resolv_timeout() in hostip.c, I think
that in case of a timeout, the signal handler for SIGALRM never
gets removed. I think that in my case it gets executed at some
point later on when execution has long left Curl_resolv_timeout()
or even the cURL library.
The code that is jumped to with siglongjmp() simply sets the
error message to "name lookup timed out" and then returns with
CURLRESOLV_ERROR. I guess that instead of simply returning
without cleaning up, the code should have a goto that jumps to
the spot right after the call to Curl_resolv().
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.
Yang Tse