[Dxspider-support] Spider stall.
djk at tobit.co.uk
Sun Oct 8 17:28:10 BST 2006
On Sun, 2006-10-08 at 16:22 +0200, Kjell Jarl wrote:
> Example netstat -tupno.
> The unkn-4 seems to appear to a windows machine.
> It is the sendqueue that fills up, it seems.
> Th rest of connections are having received queue, as the last example.
> Proto Recv-Q Send-Q Local Address Foreign Address
> State PID/Program name Timer
> tcp 125 13160 18.104.22.168:4168 22.214.171.124:9000
> ESTABLISHED 813/perl unkn-4 (69.64/0/1)
> tcp 79177 0 126.96.36.199:4160 188.8.131.52:8000
> ESTABLISHED 813/perl keepalive (2631.88/0/0)
Output problems are the bane of network programmers' lives. Most
operating systems are not good at dealing with this and it looks as
though I need to revisit the code and check that I am not blocking on
However, there has always been one area of potential blocking that I
have failed to overcome (despite quite a bit of trying) and that is for
connects to other IP addresses. Try as I might, I cannot seem to to get
the various socket commands to behave as the documentation says that
they should. The consequence of this is that if you get a rogue (or just
plain bad) DNS server not answering queries but also not sending
"network unreachable" ICMP messages, this will hang the software. Also
connects that fail to complete the TCP three way handshake (again
without sending suitable ICMP) will cause hangs.
In other words: it is network error conditions that generally cause
this, which I should (somehow) handle, but (as yet) I can't.
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