Track the connection count of a boost signal - boost

Question

What I'm trying to archive is to get an update if the number of connections to a boost::signal2::signal object is changeing.
To give you the whole picture: I'm writing a GUI application which displays data from a remote server. Each "window" in the application should get it's data for a specific dataset. If a dataset is to be displayed it needs to be remotely subscribed from the server. Multiple windows can display the same dataset (with different ordering or filtering). My goal is to subscribe to a specific dataset only ONCE and disconnect ones its not longer needed.
Background: HFT software, displaying marketdata (orderbooks, trades, ...)
My code so far: I got stuck once I tried to implement the "operator()".
enum UpdateCountMethod {
UP = 1,
DOWN = -1
};
/**
* \brief Connection class which holds a Slot as long as an instance of this class "survives".
*/
class Connection {
public:
Connection(const boost::function<void (int)> updateFunc, const boost::signals2::connection conn) : update(updateFunc), connection(conn) {
update(UP); //Increase counter only. Connection was already made.
}
~Connection() {
update(DOWN); //Decrease counter before disconnecting the slot.
connection.disconnect();
}
private:
const boost::function<void(int)> update; // Functor for updating the connection count.
const boost::signals2::connection connection; // Actual boost connection this object belongs to.
};
/**
* \brief This is a Signal/Slot "container" which number of connections can be tracked.
*/
template<typename Signature>
class ObservableSignal{
typedef typename boost::signals2::slot<Signature> slot_type;
public:
ObservableSignal() : count(0) {}
boost::shared_ptr<Connection> connect(const slot_type &t) {
// Create the boost signal connection and return our shared Connection object.
boost::signals2::connection conn = signal.connect(t);
return boost::shared_ptr<Connection>(new Connection(boost::bind(&ObservableSignal::updateCount, this, _1), conn));
}
// This is where I don't know anymore.
void operator() (/* Parameter depend on "Signature" */) {
signal(/* Parameter depend on "Signature" */); //Call the actual boost signal
}
private:
void updateCount(int updown) {
// TODO: Handle subscription if count is leaving or approaching 0.
count += updown;
std::cout << "Count: " << count << std::endl;
}
int count; // current count of connections to this signal
boost::signals2::signal<Signature> signal; // Actual boost signal
};