Many MQTT threads with the Alpakka connector

I’m yet to look into this, so I’m not quite ready to create an issue. However, I noticed that the MQTT connector (or perhaps my use of it!) is creating many, many threads. Here’s a snapshot reported by Landlord:

RESOURCE RETENTION - Process 3 has 105 thread(s) still running - check that your shutdown hooks and/or `trap` handler is shutting down all that it needs to.
Remaining threads: MQTT Rec: mqtt-gateway-2719551524279538, MQTT Call: mqtt-gateway-2719550897055238, MQTT Rec: mqtt-gateway-2719551286381638, MQTT Snd: mqtt-gateway-2719551361188338, MQTT Rec: mqtt-gateway-2719550238613838, pool-38-thread-2, MQTT Snd: mqtt-gateway-2719551591646338, MQTT Call: mqtt-gateway-2719550844081638, MQTT Disc: mqtt-gateway-2719551036021238, pool-22-thread-3, MQTT Rec: mqtt-gateway-2719550844081638, pool-67-thread-5, MQTT Disc: mqtt-gateway-2719551524279538, MQTT Disc: mqtt-gateway-2719551603957838, MQTT Disc: mqtt-gateway-2719550897055238, MQTT Disc: mqtt-gateway-2719551286381638, pool-76-thread-5, MQTT Call: mqtt-gateway-2719551361188338, MQTT Call: mqtt-gateway-2719551718634838, MQTT Disc: mqtt-gateway-2719550804533038, MQTT Disc: mqtt-gateway-2719551718634838, MQTT Disc: mqtt-gateway-2719551382177638, MQTT Con: mqtt-gateway-2719551718634838, MQTT Call: mqtt-gateway-2719551733709038, MQTT Disc: mqtt-gateway-2719550844081638, MQTT Snd: mqtt-gateway-2719550755263138, MQTT Rec: mqtt-gateway-2719550232481238, pool-68-thread-4, MQTT Snd: mqtt-gateway-2719550232481238, pool-46-thread-5, MQTT Snd: mqtt-gateway-2719551382177638, pool-11-thread-5, MQTT Call: mqtt-gateway-2719550904022938, MQTT Disc: mqtt-gateway-2719551339804338, MQTT Snd: mqtt-gateway-2719550844081638, MQTT Snd: mqtt-gateway-2719550897055238, MQTT Call: mqtt-gateway-2719550755263138, MQTT Disc: mqtt-gateway-2719551361188338, pool-15-thread-2, pool-54-thread-5, MQTT Disc: mqtt-gateway-2719550161223438, MQTT Call: mqtt-gateway-2719550238613838, MQTT Call: mqtt-gateway-2719551603957838, MQTT Snd: mqtt-gateway-2719551286381638, MQTT Rec: mqtt-gateway-2719551733709038, MQTT Con: mqtt-gateway-2719551339804338, MQTT Call: mqtt-gateway-2719551339804338, MQTT Call: mqtt-gateway-2719551036021238, MQTT Snd: mqtt-gateway-2719551733709038, MQTT Call: mqtt-gateway-2719551002797838, MQTT Rec: mqtt-gateway-2719551337786138, MQTT Rec: mqtt-gateway-2719550171110038, MQTT Snd: mqtt-gateway-2719550904022938, MQTT Call: mqtt-gateway-2719550161223438, MQTT Rec: mqtt-gateway-2719550755263138, MQTT Snd: mqtt-gateway-2719551603957838, MQTT Snd: mqtt-gateway-2719550238613838, MQTT Disc: mqtt-gateway-2719550238613838, MQTT Snd: mqtt-gateway-2719550171110038, MQTT Call: mqtt-gateway-2719551524279538, MQTT Disc: mqtt-gateway-2719551591646338, MQTT Disc: mqtt-gateway-2719550904022938, pool-28-thread-5, MQTT Rec: mqtt-gateway-2719551603957838, MQTT Call: mqtt-gateway-2719551591646338, MQTT Call: mqtt-gateway-2719551286381638, MQTT Snd: mqtt-gateway-2719551524279538, MQTT Snd: mqtt-gateway-2719551036021238, MQTT Con: mqtt-gateway-2719551337786138, MQTT Disc: mqtt-gateway-2719551337786138, MQTT Rec: mqtt-gateway-2719551036021238, pool-1-thread-5, MQTT Call: mqtt-gateway-2719550804533038, MQTT Rec: mqtt-gateway-2719551718634838, MQTT Rec: mqtt-gateway-2719551382177638, pool-59-thread-5, pool-74-thread-5, pool-26-thread-5, MQTT Rec: mqtt-gateway-2719551002797838, pool-63-thread-5, MQTT Disc: mqtt-gateway-2719551002797838, MQTT Call: mqtt-gateway-2719551337786138, MQTT Call: mqtt-gateway-2719550171110038, MQTT Disc: mqtt-gateway-2719551733709038, pool-20-thread-5, MQTT Rec: mqtt-gateway-2719550904022938, MQTT Call: mqtt-gateway-2719550232481238, pool-55-thread-5, MQTT Con: mqtt-gateway-2719550171110038, MQTT Con: mqtt-gateway-2719551002797838, pool-35-thread-5, pool-19-thread-3, MQTT Con: mqtt-gateway-2719550161223438, MQTT Snd: mqtt-gateway-2719550804533038, MQTT Rec: mqtt-gateway-2719550804533038, MQTT Disc: mqtt-gateway-2719550232481238, MQTT Disc: mqtt-gateway-2719550171110038, MQTT Call: mqtt-gateway-2719551382177638, pool-56-thread-5, MQTT Rec: mqtt-gateway-2719550161223438, MQTT Rec: mqtt-gateway-2719550897055238, MQTT Disc: mqtt-gateway-2719550755263138, MQTT Rec: mqtt-gateway-2719551339804338, MQTT Rec: mqtt-gateway-2719551361188338, MQTT Rec: mqtt-gateway-2719551591646338

As stated, it could be something I’m doing. I’m asking here mainly to see if there are any fairly recent changes to MQTT that might cause this. Thanks.

UPDATE: Perhaps this Paho issue explains it? https://github.com/eclipse/paho.mqtt.java/issues/402

I’m going to take this issue into Alpakka: https://github.com/akka/alpakka/issues/892