boolean wasLoaded = false;
Set<UUID> syncRequestedPlayers = new LinkedHashSet<>();

public void updateAndSyncFor(ServerPlayer player) {
    if (BookDataManager.get().areBooksBuilt()) {
        this.getStateFor(player).update(player);
        this.saveData.setDirty();
        this.syncFor(player);
        return;
    }
    syncRequestedPlayers.add(player.getUUID());
    wasLoaded = false;
}

//Tick server tick. Source doesn't matter as long as it is the end of the tick!
public void onServerTick(ServerTickEvent event) {
    if(event.phase == Phase.START) return;//we do this at the end of a tick.
    MinecraftServer server = getServer(); //fetch the server from somewhere.
    if(server.getTickCount() % 100 != 0) return; //We only update every 5 seconds (100 ticks)
    boolean newState = BookDataManager.get().areBooksBuilt();
    if(newState != wasLoaded) { // we only check for things if the state changed for some reason.
        if(!wasLoaded && !syncRequestedPlayers.isEmpty()) { //we only process players if we have any and the state was correct.
            PlayerList list = server.getPlayerList();
            for(UUID id : syncRequestedPlayers) {
                ServerPlayer player = list.getPlayer(id);
                if(player != null) updateAndSyncFor(player);
            }
            syncRequestedPlayers.clear();
        }
        wasLoaded = newState;
    }
}