> I guess you also mean that the clients are sending to different ports. 
> Is there no way to direct the messages to a single port and demultiplex 
> at application level? Are the messages undistinguishable when they  
> would arrive on the same socket? 
In my current implementation the clients send to the same port (resulting 
in one socket on the server side). In the final implementation each 
message would contain an ID (mostly an integer) describing which client 
send the message.  
 
Maybe it's better if I just describe what I want to do:  
On the server (running on RTAI/RTnet) should be running a periodic task. 
This task should receive every period messages from the two clients 
(running on VxWorks). Then the task performs some operations and sends 
back the clients appropriate messages back. This should all happen every 
period and - of course - in realtime.  
  
> The last resort is to create multiple threads and synchronise them when 
> required. Admittedly, this /can/ be even more inefficient than a 
> potential select/poll RT-variant (but it allows prioritisation). So, I 
> would rather try to avoid scenarios where events can arrive in an 
> unordered way on multiple channels for a single consumer. 
It is thought that all clients send their messages to the server every 
period. I didn't spend much concern about the order, I admit, since each 
message would be "labeled", containing the senders ID. But writing this, 
it also seems a bit undeterministic to me. A better (more deterministic) 
way would be: Server-Task waits for message of Client 1, reads it and 
saves it, THEN Server-Task waits for message of Client 2, and also reads 
and saves it, after this the server task performs the operations needed.  
 
If I do it this way, I also could use two sockets server-side (two 
ports), on for communication with client 1 only and one for communication 
with client 2 only.  
Would this be a better solution? Or am I overlooking something important 
when I would solve the problem this way? (Using this solution I of course 
wouldn't need a select function anymore, since one socket only receives 
one message per period).  

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