Using openwrt for armv5. Valgrind is not supported on the platform. I have gdb. Using Mosquitto client library 2.0.15 and related openSSL for secure connection.

The (relatively complex) application creates Mosquitto instance and works with it using its internal loop (special Mosquitto process supporting its operations). When application is being terminated all the things die properly, but there’s a mode when it needs to disconnect from broker, then stop the loop, then destroy the instance, perform library clean up, and then create new Mosquitto instance/loop and then connect – kind of from scratch.

The problem is when this resurrection happens, memory leaks. I am most certain it is related to the Mosquitto loop, but somehow should prove it and find out what holding memory from being released.

Bear with me if I am asking stupid or inappropriate questions here as I am not an expert in the matters.

I can see process memory growth using /proc/PID/maps and gdb’s maintenance info mappings, but there’re no details on who and what purpose allocated the memory blocks. If I would be able to tell system, at the stage of thread creation, to label memory it allocates to see in those outputs.

Back to the issue. This memory leak problem does not appear on the other platform with Mosquitto 2.0.18 (and for sure higher version of openSSL). The problem may be deeper that I think and we may suspect. Additional clue may show the fact that during stopping I call disconnect, when it returns, I call loop_stop, then destroy, and then library clean up, and in this chain exactly loop_stop returns error “invalid arguments provided”, while I use the same *mosq instance as with other calls – that’s why I have strong suspicion why this is an issue (probably does not get to the joining the thread returning the error).

I am not sure blindly digging into the Mosquitto source code, and then probably openSSL (which is being used by Mosquitto library) is a good idea.

What steps, from your expert point of views, I may take to approach the issue to get understanding what actually causes the problem? Maybe looking at open file handles (how)? Maybe somehow see what resources that exact Mosquitto thread which did not die has hijacked (per thread – how), and then try to figure out why?