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[mosquitto-dev] [question] mid (message id) in mosquitto_publish -> mosquitto_callback

Greetings everyone, it's my first time here, I hope it will be a nice journey.

First of all: I do hope that I write to proper list, I would have written on mosquitto-users but info on that pointed to mosquitto-dev.

To the topic:
* in my case mosquitto client runs in threaded mode
* `mosquitto_publish(...)` can return message id in `*mid` argument
* as it's said in docs it can be used to assure in `mosquitto_publish_callback`

I can see one issue with that: there is no guarantee that mosquitto_publish_callback won't be called prior to MID assignment which is called post mosquitto_publish. With that, we can get this scenario ( calls in order of execution in that scenario )

` pseudocode
while messages:
     if  ( mid_pos < mid_container_size ):
              mosquitto_publish --> mosquitto_callback --> try remove mid from container ( not stored yet ) --> store_mid_from_mosquitto_publish
              cant_add_mid_to_container -> some_error_handling

I could guard MID adding/removing with mutex though it seems a bit counterproductive as I could just:
- use `mosquitto_mid_generate(...)`
- store it in my mid_container
- pass it in mosquitto_publish(...)
- Result: be sure it's ready in mosquitto_callback, as there is no way that callback for this MID would be called prior to it's own send.

Of course I could just miss some important detail, or be entirely wrong - if so please be kind to fix me in my thinking it's appreciated.

Best regards,
Adam A. Dobrowolski || pholat

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