[erlang-questions] Trouble with JInterface

[Vlad Dumitrescu]

Hi Jim!

Does this happen every time, for all mailboxes?

Did you try to trace the Java code, to see if there is more information to
get?
Use -DOtpConnection.trace=3 and you will get all the activity on the
connection from the Java side (it's global, so it will be for _everything_,
you might want to try starting with a value of 1 at first and increase if
it's not enough).

regards,
Vlad


On Tue, Jan 13, 2015 at 3:39 PM, jim rosenblum <jim.rosenblum@REDACTED>
wrote:

> Folks,
>
> We are having a problem with Jinterface and Erlang 17.2. Essentially we
> have a Java/Clojure application that is using a home-brewed, Erlang,
> two-node, in-memory cache. We think the problem is either a bug with
> Jinterface or a misunderstanding on how to use it.
>
> On the Java side, we create a node and 1 to 12 unnamed mailboxes. We have
> a receive loop on each mailbox: receiving messages from Erlang, doing the
> right things with those messages, catching any errors and looping back to
> the receive. In general, everything works fine.
>
> When one of the Erlang cache-nodes goes down, the application recreates
> its mailboxes, connects to the “other” Erlang node via the new mailboxes
> and attempts to carry on. Here is where we have the problem:
>
> The Failover Protocol:
> For each mailbox
> 1. Receive loop gets OtpErlangExit
> 2. Existing mailbox is closed
> 3. New unnamed mailbox created
> 4. Application appropriate message is sent to the failover node via this
> new mailbox
> 5. Loop to the receive
>
> Symptom:
> If the receive loop has a timeout, no message is received by the new
> mailbox until AFTER the timeout fires and the loop iterates back to the
> receive. If there is no timeout specified the receive hangs (seemingly)
> forever.  We have confirmed that the failover Erlang node received the
> message (step 4) sent via the new mailbox, and that the failover Erlang
> node is sending messages to the PID representing the new mailbox —
> inspecting my server using Observer, I can see that it is sending the
> expected message to the correct PID.
>
> Our workaround is to use a short timeout in our mailbox receive loop so
> that we don’t hang for too long, but we are troubled by the thought that we
> might not understand JInterface best-practices as we are skeptical that the
> JInterface code is anything but perfect :)
>
> Is this a known issue, or does someone have any advice on how to proceed?
>
>
> Thanks,
>
> Jr0
>
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