[erlang-questions] Trouble with JInterface

[jim rosenblum]

Utilizing Vlad's suggestion of tracing via -DOtpConnection.trace showed us
where our problem was. And it was OUR problem, JInterface is just fine.

Thanks for the help.

On Tue, Jan 13, 2015 at 10:01 AM, Vlad Dumitrescu <vladdu55@REDACTED>
wrote:

> 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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>>
>>
>
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