Re: [jgroups-users] Callback for non delivered messages?

On 30.03.20 21:42, Questions/problems related to using JGroups wrote:
> Thanks Bela
> 
> I would define "delivery failure" as in, JGroups attempted to deliver a 
> message to Node X but never received an ACK or NACK for this specific 
> message.

This is not possible, as JGroups continues to try to deliver a message M 
to any member P until the message has been delivered, or P died (1) or 
got partitioned away (2).

In (1), in case P is restarted it will acquire the state (in case of a 
stateful application). This will include M (if any other member received 
it) and its effect on the state. If M was a unicast message, it won't 
get re-delivered.

In (2), a merge will merge the subgroups into one, including the state. 
This doesn't apply to unicast messages such as M, either.

> In my use case, i want to be notified of this failure to 
> deliver so that i can persist the message and reattempt delivery at a 
> later date or when Node X comes back online.

Something like persistent JMS messages? Doesn't exist in JGroups. It 
could be implemented though in a separate protocol:
* The sender of a message persists it in a shared DB
* Every message carries a unique ID, every receiver sends an ACK for 
this ID back to the sender
* When an ACK from all receivers (or a given receiver in the unicast 
case) has been received, the message will be deleted in the DB
* On restart/merge, the coordinator sends the unacked messages to a joiner



> On Mon, Mar 30, 2020 at 7:44 AM Questions/problems related to using 
> JGroups <[email protected] 
> <mailto:[email protected]>> wrote:
> 
> 
> 
>     On 27.03.20 19:22, Questions/problems related to using JGroups wrote:
>      > Is there an easy way I can get notification of delivery failure of a
>      > give message?
> 
>     What's a delivery failure? At the application level? You could use
>     RpcDispatcher and check RspList for failures (exceptions). Or use the
>     JChannel directly and send back ack messages which are collected and
>     checked by the sender.
> 
>      > Also related, Is Channel.send a blocking method?
> 
>     Not per se. However, send() can block in the following cases:
>     * The transport is TCP and the send blocks because of a full TCP
>     send-window
>     * Flow control (MFC/UFC) blocks because the receiver(s) don't send
>     enough credits back
> 
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>     -- 
>     Bela Ban | http://www.jgroups.org
> 
> 
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-- 
Bela Ban | http://www.jgroups.org