Thanks Sean. Your response forced me to read the relevant chapter in
the Stevens' "Advanced Programming in the UNIX Environment" p479 that
talks about file-descriptor passing between different processes.
In a few projects I was forced to use the IP multicast technique in
order to have multiple listeners receiving messages on the same port.
The clear advantage of the method you mentioned is that each server is
binding to a local IP address rather than an address in a multicast
range, and you don't need to worry about multicast filtering by routers.
Perhaps there are other beneficial uses of this technique...
Serge
Sean Hinde wrote:
>> I believe the duplicate bindings (i.e. to the same IP address and
>> port) are *only* possible for UDP multicast binds. TCP doesn't
>> support this and should always fail with eaddrinuse if another
>> process is active and is bound to that socket. UDP non-multicast
>> binds with {reuseaddr, true} will allow you to "steal" a socket from
>> another process (without that process knowing about it), yet the
>> kernel will only deliver UDP messages to the latest process that
>> bound the UDP socket.
>
>
> Not entirely true. For UDP it is possible to dup the UDP file
> descriptor into several UNIX processes and the OS will send UDP
> datagrams to any of them.
>
> Relevant stuff here:
>
> http://forums.trapexit.org:81/phpBB/viewtopic.php?
> t=3250&postdays=0&postorder=asc&highlight=file+descriptor&start=15
>
>
> Sean
>
>
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