public void load(ArrayList<AirspaceArea> areas, String storage) {
    this.storage = storage;
    try {

      File extpath = Storage.getStorage(storage);
      File srcpath = new File(extpath, Config.path + "clearance.dat");
      FileInputStream fs = new FileInputStream(srcpath);
      DataInputStream ds = new DataInputStream(fs);
      HashMap<String, ArrayList<AirspaceArea>> id2areas =
          new HashMap<String, ArrayList<AirspaceArea>>();
      for (AirspaceArea a : areas) {
        a.cleared = 0;
        String id = a.getIdentity();
        ArrayList<AirspaceArea> l = id2areas.get(id);
        if (l == null) {
          l = new ArrayList<AirspaceArea>();
          id2areas.put(id, l);
        }
        l.add(a);
      }
      int version = ds.readByte();
      if (version != 1) throw new RuntimeException("Unknown on-disk format");
      int len = ds.readInt();
      for (int i = 0; i < len; ++i) {
        String id = ds.readUTF();
        long when = ds.readLong();
        ArrayList<AirspaceArea> l = id2areas.get(id);
        if (l != null) for (AirspaceArea a : l) a.cleared = when;
      }
    } catch (Throwable e) {
      e.printStackTrace();
      Log.i("fplan", "Couldn't load clearances");
    }
  }
 @Override
 protected Void doInBackground(ArrayList<AirspaceArea>... params) {
   try {
     if (params.length == 0) return null;
     ArrayList<AirspaceArea> last = params[params.length - 1];
     File extpath = Storage.getStorage(storage);
     File tmppath = new File(extpath, Config.path + "clearance.dat.tmp");
     File dstpath = new File(extpath, Config.path + "clearance.dat");
     FileOutputStream fs = new FileOutputStream(tmppath);
     DataOutputStream ds = new DataOutputStream(fs);
     ds.writeByte(1); // Version
     ArrayList<String> cleared = new ArrayList<String>();
     ArrayList<Long> clearedwhen = new ArrayList<Long>();
     long now = new Date().getTime();
     for (AirspaceArea a : last) {
       long ago = now - a.cleared;
       if (ago > Config.clearance_valid_time) a.cleared = 0;
       if (a.cleared != 0) {
         cleared.add(a.getIdentity());
         clearedwhen.add(a.cleared);
       }
     }
     ds.writeInt(cleared.size());
     for (int i = 0; i < cleared.size(); ++i) {
       String id = cleared.get(i);
       Long when = clearedwhen.get(i);
       ds.writeUTF(id);
       ds.writeLong(when);
     }
     tmppath.renameTo(dstpath);
   } catch (Throwable e) {
     e.printStackTrace();
     Log.i("fplan", "Couldn't persist clearances");
   }
   return null;
 }