In this case callbacks will be called in a sequence because we aren’t using threads in the library. Therefore we cannot execute the callbacks, bound to the same lcb_t handle, simultaneously.
But if you are going to run event loop (with the my_get_callback()) in one thread, but schedule the GET operations from the another thread (calling lcb_get(…)), you will get issues. Because on lcb_get() you are writing to the internal buffer, and after calling the appropriate callback it will flush the buffer.