What are in-flight messages inside JBoss?

Question

I have not been able to find a clear definition of what is an in-flight message inside Jboss EAP 6.

Right now I am see that I have 4 messages stuck in-flight inside JBoss

If i connect through JMSToolBox to that queue I don't see anything inside. Only after I restart the jboss server they are gone from in-flight.

So what exactly is an in-flight message?

Answer 1

In JMS terms, in flight would mean a message that has been delivered but has not yet:

1. Been auto-acknowledged, or
2. Been client-acknowledged, or
3. Is enrolled in a transaction which has not yet committed.

Answer 2

Messages "in flight" are messages that have already been delivered but not further acted on by the consumer.

Messages are considered in flight if they have been sent to a client but have not yet been deleted or have not yet reached the end of their visibility window.

Answer 3

Simply, the number of messages sent to a consumer session and have not received an ack.