On Sun, 18 Dec 2011, Pedro Larroy wrote:
(lib/asyn-ares.c:288)
My interpretation is that there's this poll call waiting for the dns query
to finish in the ares_channel associated with the current curl_handle thus:
But that's not right. At least that's not how it is meant to work.
When the multi interface function is called due to activity on a socket and
the multi handle's internal state is in CURLM_STATE_CONNECT then it will call
the funtions that then trickles down to a call to
lib/asyn-ares.c:waitperform(). The handle should then move on to the
CURLM_STATE_WAITRESOLVE state if the resolve didn't immediately happen.
As you can see, it calls the function with a timeout of 0. It is just a
single-time check if there's anything to do, and it then returns all the way
back to your application. It is not a block.
* It will block the whole program until the current dns reply is
recieved, which goes against the paradigm of the multi interface usage
with asynchronous IO.
Why would it? It checks with a timeout of 0, that means it returns
immediately.
* If that wasn't bad enough, the select has a timeout of 0.
Why is that bad? It means it won't block!
* I have already observed degradation and blocking which was very
detrimental and tracked down to this.
Then you've found a bug we should fix. I still don't see it though.
I think it's going to be difficult to fix since the multi api exposes one
socket perl curl handle
No it doesn't. The API provides socket(s) or fd_sets, there's no limitation or
restriction in the API which says libcurl will only use one socket.
so it would have to expose all the sockets of the dns resolution per handle
to function properly, which seems not trivial.
Sorry, but I claim it already exposes "all the sockets of the dns resolution
per handle". See the lib/asyn-ares.c:Curl_resolver_getsock() funtion, which is
called from the multi_getsock() function which is used to figure out all the
sockets a particualr curl handle is using and what action to wait for on
those sockets.
--
/ daniel.haxx.se
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