12 Nov
2008
12 Nov
'08
11:16 a.m.
On Nov 12, 2008 at 10:33, Klaus Darilion <klaus.mailinglists(a)pernau.at> wrote:
Interesting. Is it really completely asynchronous with any blocking, or
is it handed over to a dedicated "TCP send" process which is then blocked?
Yes, it's completely asynchronous, no process is blocked.
A brief description on how it's working for send on an already opened
connection:
- check if the connection has data buffered. If it does it means that
either is still connecting or a previous send failed to be executed
in-place and queued the data => add to the queued data, return.
- if no data buffered try non-blocking send. If it fails queue data
to the ser internal tcp connection structure and enable waiting for
POLLOUT events (socket send buffer has enough space). return.
For connect is similar: connect() non blocking, queue data, return.
When a socket can be written, the main tcp process will write the queued
data (or as much as possible from it).
-
Yes.
Andrei
Andrei Pelinescu-Onciul schrieb:
Sorry for the name, I was not talking about a full resolver.
The DNS cache uses in fact a minimalistic resolver. We would just need to
replace res_search with a res_mkquery and then "manually" send the
request and wait for an answer in a poll() loop (we won't actually use
poll, but the io_wait.h optimized stuff that uses epoll(), kqueue() a.s.o
depending on the system).
We don't need a recursive resolver, we only need something minimal.
One should still use a close DNS server since the internal resolver does
not support recursive queries, DNSSEC a.s.o (we could add them, but so
far there would be little benefit).
[crossposting since this is of general interest]
On Nov 12, 2008 at 00:30, Klaus Darilion <klaus.mailinglists(a)pernau.at>
wrote:
Ok. I see.
Hi Miklos!
This sounds great. Can you make a sample function which uses the new
feature?
We are thinking of doing a dns_prefetch module using this.
The sip-router.cfg will look like:
route{
...
dns_prefetch("uri", ROUTE_DNS_OK);
# end of script
}
route[ROUTE_DNS_OK]{
if (dns_error){
...
}
# continue normal processing
# the uri was resolved and is in the dns cache
...
t_relay()
...
} However don't expect something quickly as
everybody is quite busy and we
would still need to write a dns resolver process pool (time consuming).
I still wonder if the DNS resolver in ser is really a good idea. For
example if you take a look at bind, it is really mature and still they
fix several issues with each release - and doing all the tricks to avoid
cache poisoning and handling DNSSEC correctly is not easy. Thus, maybe
having a DNS cache in ser can make sense, but having a full resolver IMO
not. Can this
also be used for DNS lookups and TCP/TLS connection setup?
Yes for DNS (see above) and in general for any route-level async
processing
involving tm (e.g. lookup some part of the message in a slow DB and
execute automatically another route when the DB responds).
It cannot be used for TCP/TLS, but it's not needed anyway. In ser TCP
connection setup and TCP send is already asynchronous, at least if
you have tcp_buf_write=yes in ser.cfg (I agree it's not a very well (BTW: most of the core new options documentation
in ser can be found
in NEWS)
Probably this should be merged too.