Investigate concurrency support for the MqttPahoMessageDrivenChannelAdapter

[artembilan]

Affects Version(s): <Spring Integration version>

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[luisfranciscob]

Does this open issue mean that the current implementation of MqttPahoMessageDrivenChannelAdapter is single threaded?

[artembilan]

The underlying Paho Client is single-threaded.
It does have two loops:

1. CommsReceiver.run() to read data from the MqttInputStream - mostly messages for the subscibed topics.
2. CommsCallback.run() to deliver those messages from an in-memory queue to the subscribed listeners in the application.

So, generally speaking: we always get delivery for all the topic we have subscribed in a single thread.
That's technically a point of this issue: to be able to distribute topics subscription between concurrency configured.