Kalnichevski, Oleg wrote:
Odi, If there's enough confidence that setting linger time to 0 will not have an unexpected adverse effect, the fix can be included into 2.0. I do not know TCP/IP that well to make that call, though.
Oleg
From RFC-739 3.5:
When a connection is closed actively, it MUST linger in TIME-WAIT state for a time 2xMSL (Maximum Segment Lifetime). However, it MAY accept a new SYN from the remote TCP to reopen the connection directly from TIME-WAIT state, if it:
1. assigns its initial sequence number for the new connection to be larger than the largest sequence number it used on the previous connection incarnation, and
2. returns to TIME-WAIT state if the SYN turns out to be an old duplicate.
Some more information on what setSoLinger() does:
Specify a linger-on-close timeout. This option disables/enables immediate return from a close() of a TCP Socket. Enabling this option with a non-zero Integer timeout means that a close() will block pending the transmission and acknowledgement of all data written to the peer, at which point the socket is closed gracefully. Upon reaching the linger timeout, the socket is closed forcefully, with a TCP RST. Enabling the option with a timeout of zero does a forceful close immediately.
From the kernel archives:
Setting linger to zero to zap time waiters is not only anti-social, the various IP working groups state that it is strongly discouraged upon, both in the RFC's and elsewhere. The TIME_WAIT state was created for a specific purpose, by zapping the socket before the TIME_WAIT timeout occurs you are defeating the purpose of it.
Even FreeBSD's stack has this old linger==0 behavior totally removed.
So I guess setting SO_LINGER to zero could:
a) not work at all
b) have adverse effects on reliability (possible data loss in the last packet)
I am not an expert on TCP either, so maybe someone with indepth knowledge about the close handshake could advise us what to do here. It's certainly not something that should go into 2.0 though. Just too risky.
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