On 04/11/2016 01:28 AM, Erik Hugne wrote:
> On Apr 10, 2016 15:27, "Leon Pollak" <le...@plris.com> wrote:
>> After your answer I again looked through the both manuals and did not find
>> anything saying that connectionless messaging allows drops. Vice verse,
> the
>> programmer's manual explicitly states that "TIPC is designed to be a
> reliable
>> messaging mechanism, in which an application can send a message and assume
>> that the message will be delivered to the specified destination as long as
>> that destination is reachable."
>>
>> Now, is it a bug, corrected in Nov 6th 2013? Or a feature?
If it is a bug, the bug is in the manual, because we we cannot guarantee
sequenctial, loss-free delivery using SOCK_DGRAM or SOCK_RDM.
First, this comes from the very definition of those two communication
modes, second it is a practical impossibility to guarantee this 100% with
connectionless while retaining any reasonable performance.
What was corrected in the aforementioned commit was the buffer
allocation problem, which Erik describes correctly below. That was a bug.
But we still cannot guarantee connectionless delivery socket-to-socket,
because an overwhelmed receiving socket will have to toss messages away
when its receive buffer is full.
>>
>> i can't move to connection oriented methods, because I need to support
> one-
>> to-3 and 3-to-one.
As I see it you have three options here:
- Set up three connections via three different sockets pairs.
- Make your own end-to-end flow control at user level (it is not hard)
- Possibly increasing server priority, as Erik is suggesting. But this gives
you no absolute guarantee.
//jon
>>
> This sounds a lot like the problem when connectionless messages are
> received, acked on the tipc link layer and passed to the socket, but
> dropped there because the socket receive buffer is full.
> If the receiving application does not drain the queue faster than messages
> build up, there will be losses as there us no concept of flow control at
> this level.
> Try bumping the prio of the server, maybe run it as an rt thread?
>
> //E
>
>> Sorry.
>> --
>> Leon
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