class A
{
/* has signals2::signal(s) for callbacks, fired when completion-handler of
various async operations are invoked (eg., async_read_until etc) */
};

class B
{
void registerListenersWith_A()
{
        /* has member-function listeners submitted to signals of class A eg., auto
self = shared_from_this();
shared_ptr_A->someSig_A.connect([self]{self->mem_func_B();}); */
}
void disconnectListenersWith_A()
{
        /* disconnect all boost::signals2::connection(s) made above */
}
};

auto shared_ptr_A = std::make_shared< A >();
{
auto shared_ptr_B = std::make_shared< B >();
give shared_ptr_B a copy of shared_ptr_A for use above.
shared_ptr_B->registerListenersWith_A();
//....some operations here.....
shared_ptr_B->disconnectListenersWith_A();
} //i want pointer managed by shared_ptr_B to be destroyed here in a
thread-safe manner (ie., no pending calls remain from A to B etc.