AMQP metrics report negative number of authenticated connections

Periodically(I would say rather sporadically !) AMQP adapter report a negative metric number for authenticated connections. Unfortunately, for a while I tried to find the cause and reproduce this but without success. But anyway, when I took a look at MicrometerBasedMetrics.java, I would like to propose to have more safe incremental and detrimental operations for connections counters, something like this:

private void tryToDecrement(AtomicLong longValue) {
   longValue.getAndUpdate(oldValue -> oldValue > 0 ? oldValue - 1 : 0);
}

private void tryToIncrement(AtomicLong longValue)
 {
  longValue.getAndUpdate(oldValue -> {
   if (oldValue == Long.MAX_VALUE) {
    throw new IllegalStateException("Long value overflow!");
   }
   return oldValue + 1L;
  });
 }
}

[fkaltner]

I think I found the cause:

In the AMQP adapter the connection count was incremented when opening a new connection after checking if the adapter’s connection limit was hit. The decrement however was done in any case, since it is part of the connection’s close handler.

As you can see in e70476c I fixed this by moving the increment of the connection count to the connection’s open handler.

Nevertheless I am not sure of any side-effects. @kaniyan / @sophokles73 WDYT?

[fkaltner]

I am able to reproduce this on my machine by setting the AMQP / MQTT adapter’s connection limit to 1 and connecting 2 clients.

When I connect the second client, I see negative values in the Prometheus dashboard.

I’d like to continue to investigate this, @sophokles73 can you assign this issue to me?