BlockUC和Replica

  /**
   * Block replica states, which it can go through while being constructed.
   */
  enum ReplicaState {
    /** Replica is finalized. The state when replica is not modified. */
    FINALIZED(0),
    /** Replica is being written to. */
    RBW(1),
    /** Replica is waiting to be recovered. */
    RWR(2),
    /** Replica is under recovery. */
    RUR(3),
    /** Temporary replica: created for replication and relocation only. */
    TEMPORARY(4);

    private static final ReplicaState[] cachedValues = ReplicaState.values();

    private final int value;

    ReplicaState(int v) {
      value = v;
    }

    public int getValue() {
      return value;
    }

    public static ReplicaState getState(int v) {
      return cachedValues[v];
    }

    /** Read from in */
    public static ReplicaState read(DataInput in) throws IOException {
      return cachedValues[in.readByte()];
    }

    /** Write to out */
    public void write(DataOutput out) throws IOException {
      out.writeByte(ordinal());
    }
  }

  /**
   * States, which a block can go through while it is under construction.
   */
  enum BlockUCState {
    /**
     * Block construction completed.

     * The block has at least the configured minimal replication number
     * of {@link ReplicaState#FINALIZED} replica(s), and is not going to be
     * modified.
     * NOTE, in some special cases, a block may be forced to COMPLETE state,
     * even if it doesn't have required minimal replications.
     */
    COMPLETE,
    /**
     * The block is under construction.

     * It has been recently allocated for write or append.
     */
    UNDER_CONSTRUCTION,
    /**
     * The block is under recovery.

     * When a file lease expires its last block may not be {@link #COMPLETE}
     * and needs to go through a recovery procedure, 
     * which synchronizes the existing replicas contents.
     */
    UNDER_RECOVERY,
    /**
     * The block is committed.

     * The client reported that all bytes are written to data-nodes
     * with the given generation stamp and block length, but no 
     * {@link ReplicaState#FINALIZED} 
     * replicas has yet been reported by data-nodes themselves.
     */
    COMMITTED
  }