Sockets stuck in CLOSED state...
freebsd-questions at transip.nl
Wed Jun 18 14:36:12 UTC 2008
Recently i've been upgrading some of my machines from FreeBSD 6.x amd64
to FreeBSD 7.0 amd64.
After upgrading I noticed a weird error/bug. It seems that after several
thousand TCP connections some seem to hang in 'CLOSED' state.
netstat -n gives:
tcp4 0 0 126.96.36.199.* 188.8.131.52.42149 CLOSED
tcp4 39 0 184.108.40.206.* 220.127.116.11.54103 CLOSED
tcp4 35 0 18.104.22.168.* 22.214.171.124.41718 CLOSED
tcp4 38 0 126.96.36.199.* 188.8.131.52.55618 CLOSED
tcp4 41 0 184.108.40.206.* 220.127.116.11.44230 CLOSED
tcp4 39 0 18.104.22.168.* 22.214.171.124.49439 CLOSED
These never go away; they gradually increase and increase until the
application starts giving errors (probably because some socket or
filedescriptor limit is reached). When the application is killed these
The application in question is a self written DNS server, multithreaded,
and running fine for years without any troubles on both BSD 5.x as well
as 6.x. Also 32bits as well as 64bits on 6.x.
Ofcourse that doesn't mean that the application is error free, however,
after doing extensive testing I really can not find anything wrong with
the application itself, so I'm thinking maybe there's a change somewhere
that causes this? I know that tcp/network has been completely redone...
What basically happens in the application is this:
- one main tcp thread runs an infinite while loop waiting for new
connections to arrive
- as soon as one arrives a new thread is spawned that handles the
newly created stream
- it reads some bytes, writes some bytes, then closes it
- thread exits
What appears to happen is this: after the new thread is spawned it tries
to read 2 bytes (DNS tcp length information). It gets back 0 bytes (EOF)
and therefore closes the sockets and calls pthread_exit. However in
netstat that same stream oftenly appears to have bytes 'stuck' in the in
I really can't see how this can cause hanging sockets in 'CLOSED' state.
Even if the incoming queue isnt read entirely a call to close should
close it. Also I really can't find any documentation in netstat, or
elsewhere, about the 'CLOSED' state...
Any help would greatly be appreciated!
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