[rabbitmq-discuss] Fwd: [PATCH] Make the Erlang RabbitMQ Client shut down gracefully

Simon MacMullen simon at rabbitmq.com
Thu Dec 19 10:49:21 GMT 2013

Thanks for the patch (it may not get looked at until 2014 now though...)

I don't think the original mail was filtered BTW - what made you think 
it was?

Cheers, Simon

On 18/12/13 21:56, Jesper Louis Andersen wrote:
> Resending this to avoid the spam filter. It patches rmqs Erlang client
> to spam way less.
> ---------- Forwarded message ----------
> From: "Jesper Louis Andersen"
> <jesper.louis.andersen at erlang-solutions.com
> <mailto:jesper.louis.andersen at erlang-solutions.com>>
> Date: Dec 18, 2013 3:15 PM
> Subject: [PATCH] Make the Erlang RabbitMQ Client shut down gracefully
> To: "Discussions about RabbitMQ" <rabbitmq-discuss at lists.rabbitmq.com
> <mailto:rabbitmq-discuss at lists.rabbitmq.com>>
> Cc:
> Hi RMQ developers,
> The following patch changes the behaviour of the RMQ Erlang Client when
> it shuts down. It avoids spamming the log with death messages in
> graceful closes. Background is below the patch.
> Patch:
> https://github.com/issuu/amqp_client/commit/2c582c983433027e007b4e80f2c6d9f25d7f854b
> https://github.com/issuu/amqp_client/commit/2c582c983433027e007b4e80f2c6d9f25d7f854b.patch
> Background:
> The RMQ Erlang client holds a supervisor tree which contains processes
> running as amqp_gen_consumers where a direct_consumer module has been
> injected. A typical user of the client application will have its own
> separate supervisor tree. To handle the crash of the client application,
> the direct_consumer installs a *monitor* on the ConsumerPid. This allows
> us to stop consumption if the consumer process goes away for some reason.
> OTP compliant processes will have two kinds of exit reasons which are
> graceful: "normal" and "shutdown". The former happens when the
> ConsumerPid exits normally. Either by calling exit(normal) or by
> returning from the top-level function. The latter happens if the
> supervisor decides to close down the tree. It normally sends forth
> exit(Child, shutdown) in order to shut down its supervisor children
> processes. Any other exit reason is a grace error.
> Implementation:
> The patch detects the two cases of graceful shutdowns and then proceeds
> to silently close the supervision tree on the RabbitMQ side. This stops
> such errors from spamming in the logs when the supervisor tree closes
> down normally. If other errors occur, we close down the tree like we
> always have, yelling and screaming that something is going very wrong.
> Review:
> The patch has seen some internal testing and looks correct; but as I am
> not too well versed in the supervisor tree, and in particular the
> supervisor2 structure, I might have introduced a leak. Please look
> closely at the code with respect to crashing and stopping behaviour in
> mind. If supervisor2 works anything like supervisor here, it should work.
> +++
> I hope the RabbitMQ developers will consider this patch for inclusion as
> it might help others. It is yours to use and I hereby sign it off as a
> RabbitMQ contribution.
> Merry Christmas :)
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Simon MacMullen
RabbitMQ, Pivotal

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