On Wed, 2017-12-06 at 12:55 +0100, Francesco wrote:
> Hi all,
> As you know when using PUB/SUB model the order of arrival of messages
> at
> SUB-side cannot be garantueed and generally speaking, the SUB will
> receive
> messages out of order. This is a well known problem, see e.g.:
>   https://cloud.google.com/pubsub/docs/ordering
> 
> My question is: in case in the SUB you need strict time ordering, are
> you
> aware of any good C++ implementation of a reordering queue?
> 
> I used for other purposes moodycamel's queue (
> http://moodycamel.com/blog/2013/a-fast-lock-free-queue-for-c++) which
> is
> thread-safe but it does not perform time-reordering.
> 
> Thanks!
> 
> Francesco

What do you mean exactly? If you mean with multiple publishers writing,
or ordering between different subscribers, then yeah it cannot be
guaranteed.

But from each individual publisher, to each individual subscriber, the
ordering is guaranteed. Messages are written in a queue (first-in
first-out), and then given to TCP, and then again received in a queue
where the application fetches them from.

-- 
Kind regards,
Luca Boccassi

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