ConcurrentModificationException on channel manager closing

[kirtanparmar]

Describe the bug

Hello

I have developed an Android app with RMQ in which I am utilizing 2 RMQ (RMQ1, RMQ2) with 2 channel for each RMQ (One for publishing and one for consuming).

Currently I am facing an issue related to "java.util.ConcurrentModificationException" which is occurring in "com.rabbitmq.client.impl.ChannelManager.scheduleShutdownProcessing".

Please note that when I face this issue, at that time Android device was in doze mode.

Below I have provided logs for reference. (Replaced actual amqp link with "guest@X.Y.Z.A:1234/Example" and "guest@X.Y.Z.B:1234/Example")

Sep 12, 2025 @ 04:20:23.613 | Connection shutdown on rmq2.example.com : reason= null
Sep 12, 2025 @ 04:20:23.616 | Connection shutdown on rmq1.example.com : reason= null
Sep 12, 2025 @ 04:34:02.077 | rmq1.example.com connection recovery started
Sep 12, 2025 @ 04:34:02.077 | rmq2.example.com connection recovery started
Sep 12, 2025 @ 04:34:02.535 | Connection amqp://guest@X.Y.Z.A:1234/Example has recovered
Sep 12, 2025 @ 04:34:02.537 | Connection amqp://guest@X.Y.Z.B:1234/Example has recovered
Sep 12, 2025 @ 04:34:02.580 | Channel AMQChannel(amqp://guest@X.Y.Z.A:1234/Example,1) has recovered
Sep 12, 2025 @ 04:34:02.585 | Channel AMQChannel(amqp://guest@X.Y.Z.B:1234/Example,1) has recovered
Sep 12, 2025 @ 04:34:02.618 | Channel AMQChannel(amqp://guest@X.Y.Z.B:1234/Example,2) has recovered
Sep 12, 2025 @ 04:34:02.619 | Channel AMQChannel(amqp://guest@X.Y.Z.A:1234/Example,2) has recovered
Sep 12, 2025 @ 04:34:02.619 | Recovering RecordedConsumer[tag=ConsumerAPP, queue=1c336ca0e0480023ca91b508d46772d8db88a68f8549bc41b86122d7144e7e93639bd090b1c35eb02c9c4c5fc49e2b66725fd9249ed17dc3b42579c15dbe995e, autoAck=false, exclusive=false, arguments=null, consumer=example.app.rabbitmq.RabbitMQHelper$consumeBSNHashQueue$1@2efbeef, channel=AMQChannel(amqp://guest@X.Y.Z.B:1234/Example,2)]
Sep 12, 2025 @ 04:34:02.619 | Recovering RecordedConsumer[tag=ConsumerAPP, queue=1c336ca0e0480023ca91b508d46772d8db88a68f8549bc41b86122d7144e7e93639bd090b1c35eb02c9c4c5fc49e2b66725fd9249ed17dc3b42579c15dbe995e, autoAck=false, exclusive=false, arguments=null, consumer=example.app.rabbitmq.RabbitMQHelper$consumeBSNHashQueue$1@7a7b4d0, channel=AMQChannel(amqp://guest@X.Y.Z.A:1234/Example,2)]
Sep 12, 2025 @ 04:34:02.646 | RecordedConsumer[tag=ConsumerAPP, queue=1c336ca0e0480023ca91b508d46772d8db88a68f8549bc41b86122d7144e7e93639bd090b1c35eb02c9c4c5fc49e2b66725fd9249ed17dc3b42579c15dbe995e, autoAck=false, exclusive=false, arguments=null, consumer=example.app.rabbitmq.RabbitMQHelper$consumeBSNHashQueue$1@2efbeef, channel=AMQChannel(amqp://guest@X.Y.Z.B:1234/Example,2)] has recovered
Sep 12, 2025 @ 04:34:02.647 | rmq2.example.com connection recovered
Sep 12, 2025 @ 04:34:02.648 | RecordedConsumer[tag=ConsumerAPP, queue=1c336ca0e0480023ca91b508d46772d8db88a68f8549bc41b86122d7144e7e93639bd090b1c35eb02c9c4c5fc49e2b66725fd9249ed17dc3b42579c15dbe995e, autoAck=false, exclusive=false, arguments=null, consumer=example.app.rabbitmq.RabbitMQHelper$consumeBSNHashQueue$1@7a7b4d0, channel=AMQChannel(amqp://guest@X.Y.Z.A:1234/Example,2)] has recovered
Sep 12, 2025 @ 04:34:02.648 | rmq1.example.com connection recovered
Sep 12, 2025 @ 04:34:02.761 | Uncaught Exception Handler: caught exception -> java.util.ConcurrentModificationException

Here is the stack trace for the exception.

nullat java.util.HashMap$HashIterator.nextNode(HashMap.java:1603)
at java.util.HashMap$KeyIterator.next(HashMap.java:1626)
at java.util.AbstractCollection.addAll(AbstractCollection.java:335)
at java.util.HashSet.(HashSet.java:121)
at com.rabbitmq.client.impl.ChannelManager.scheduleShutdownProcessing(Unknown Source:4)
at com.rabbitmq.client.impl.ChannelManager.handleSignal(Unknown Source:98)
at com.rabbitmq.client.impl.AMQConnection.finishShutdown(Unknown Source:4)
at com.rabbitmq.client.impl.AMQConnection.shutdown(Unknown Source:4)
at com.rabbitmq.client.impl.AMQConnection.handleFailure(Unknown Source:20)
at com.rabbitmq.client.impl.AMQConnection.access$500(Unknown Source:0)
at com.rabbitmq.client.impl.AMQConnection$MainLoop.run(Unknown Source:39)
at java.lang.Thread.run(Thread.java:1119)

Please help.

Reproduction steps

This happens very rarely. So far I have found 2 instances. And if this increases then it will affect application quality.

Expected behavior

I do not know if I am doing anything wrong or not because, recovery happens automatically.

Additional context

Android application and android device was in doze mode.

[acogoluegnes]

Client and broker version?

This part of the code could use some synchronization, I'll work on a fix.