Potential deadlock in AutorecoveringConnection

[maxbrodin]

The code in AutorecoveringConnection.java acquires synchronization objects in different order (once acquires consumers and then recordedQueues, another time acquires recordedQueues and then consumers).

Acquiring synchronization objects in different order can cause circular wait (deadlock).

The first order is: (1) first acquire consumers and then recordedQueues:

• enter public method excludeQueueFromRecovery() at line 984
• acquire synchronization on consumers at line 987
• acquire synchronization on recordedQueues at line 988

The second order is: (2) first acquire recordedQueues and then consumers:

• enter public method recoverQueue() at line 715
• acquire synchronization on recordedQueues at line 732
• call deleteRecordedQueue() at line 740
• call maybeDeleteRecordedAutoDeleteExchange() at line 973
• acquire synchronization on consumers at line 1035

initially reported by Adrian Nistor

[michaelklishin]

@maxbrodin a PR that changes the order to be identical would be considered.

[michaelklishin]

As my investigation in #649 suggests, the right thing to do is to not acquire a lock on this.consumers in AutorecoveringConnection#maybeDeleteRecordedAutoDeleteExchange instead.