+ *
+ * Aquisition/release:
+ * ------------------
+ * Each service has a dependent-count ("required_by"). This starts at 0, adds 1 if the
+ * service has explicitly been started (i.e. "start_explicit" is true), and adds 1 for
+ * each dependent service which is not STOPPED (including depdendents with a soft dependency).
+ * When required_by transitions to 0, the service is stopped (unless it is pinned). When
+ * require_by transitions from 0, the service is started (unless pinned).
+ *
+ * So, in general, the dependent-count determines the desired state (STARTED if the count
+ * is greater than 0, otherwise STOPPED). However, a service can be issued a stop-and-take
+ * down order (via `stop(true)'); this will first stop dependent services, which may restart
+ * and cancel the stop of the former service. Finally, a service can be force-stopped, which
+ * means that its stop process cannot be cancelled (though it may still be put in a desired
+ * state of STARTED, meaning it will start immediately upon stopping).
+ *
+ * Pinning
+ * -------
+ * A service may be "pinned" in either STARTED or STOPPED states (or even both). Once it
+ * reaches a pinned state, a service will not leave that state, though its desired state
+ * may still be set. (Note that pinning prevents, but never causes, state transition).
+ *
+ * The priority of the different state deciders is:
+ * - pins
+ * - force stop flag
+ * - desired state (which is manipulated by require/release operations)
+ *
+ * So a forced stop cannot occur until the service is not pinned started, for instance.