[SR-Users] Kamailio propagates 180 and 200 OK OUT OF ORDER

[Alex Balashov]

On Wed, Apr 08, 2020 at 12:30:45PM -0400, Greg Troxel wrote:

> I don't see this as being about the nature of parallel processing.

It absolutely is -- when it comes to explaining why Kamailio behaves the
way it does.

It bears remark that it's not a common occurrence; if Kamailio could not
be relied upon to forward messages in a FIFO order on a widespread
basis, it wouldn't be very useful. This race occurs, in my experience,
in highly contended environments, e.g. a VM on a busy hypervisor.

> Either the protocol specifications have ordering rules (in which case
> an implementation which does not follow those is defective), or they
> do not have ordering rules (in which case an implementation that is
> troubled by lack of ordering is defective).

And yet, SIP-as-specified is replete with race conditions.

One way to look at this: if you want guaranteed ordering
(network-introduced ordering issues not withstanding), use a single
child process. If you want "enhanced performance", use multiple child
processes, with the understanding that this entails a small amount of
risk as a trade-off. :-)

-- Alex

-- 
Alex Balashov | Principal | Evariste Systems LLC

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