private long now(boolean alreadyExpired) {
        return alreadyExpired ? 0 : System.currentTimeMillis();
    }
Acquire a snapshot of all configs with the same generation within a timeout.

@param timeoutInMillis timeout to wait in milliseconds
@param requireChange if set, at least one config have to change
@return true, if a new config generation has been found for all configs (additionally requires
        that at lest one of them has changed if <code>requireChange</code> is true), and
        the config should be applied at this time, false otherwise
config/src/main/java/com/yahoo/config/subscription/ConfigSubscriber.java