Why do my RabbitMQ channels keep closing?

Question

I'm debugging some Java code that uses Apache POI to pull data out of Microsoft Office documents. Occasionally, it encounter a large document and POI crashes when it runs out of memory. At that point, it tries to publish the error to RabbitMQ, so that other components can know that this step failed and take the appropriate actions. However, when it tries to publish to the queue, it gets a com.rabbitmq.client.AlreadyClosedException (clean connection shutdown; reason: Attempt to use closed channel).

Here's the error handler code:

try {
    //Extraction and indexing code
}
catch(Throwable t) {
    // Something went wrong! We'll publish the error and then move on with
    // our lives
    System.out.println("Error received when indexing message: ");
    t.printStackTrace();
    System.out.println();
    String error = PrintExc.format(t);
    message.put("error", error);

    if(mime == null) {
        mime = "application/vnd.unknown";
    }

    message.put("mime", mime);
    publish("IndexFailure", "", MessageProperties.PERSISTENT_BASIC, message);
}

For completeness, here's the publish method:

private void publish(String exch, String route, 
    AMQP.BasicProperties props, Map<String, Object> message) throws Exception{
    chan.basicPublish(exch, route, props, 
        JSONValue.toJSONString(message).getBytes());  
}

I can't find any code within the try block that appears to close the RabbitMQ channel. Are there any circumstances in which the channel could be closed implicitly?

EDIT: I should note that the AlreadyClosedException is thrown by the basicPublish call inside publish.

Answer 1

An AMQP channel is closed on a channel error. Two common things that can cause a channel error:

• Trying to publish a message to an exchange that doesn't exist
• Trying to publish a message with the immediate flag set that doesn't have a queue with an active consumer set

I would look into setting up a ShutdownListener on the channel you're trying to use to publish a message using the addShutdownListener() to catch the shutdown event and look at what caused it.