spark 2.0 OneForOneStreamManager

OneForOneStreamManager只能按顺序一个接一个的读取一个流的数据块。它借助于内部的StreamSate类，StreamState类里存放了客户端编号，ManagedBufffer的迭代器，以及当前读的块编号。要读的块编号必须为当前块编号加1。

/** * StreamManager which allows registration of an Iterator<ManagedBuffer>, which are * individually fetched as chunks by the client. Each registered buffer is one chunk. */public class OneForOneStreamManager extends StreamManager {  private final Logger logger = LoggerFactory.getLogger(OneForOneStreamManager.class);  private final AtomicLong nextStreamId;  private final ConcurrentHashMap<Long, StreamState> streams;  /** State of a single stream. */  private static class StreamState {    final String appId;    final Iterator<ManagedBuffer> buffers;    // The channel associated to the stream    Channel associatedChannel = null;    // Used to keep track of the index of the buffer that the user has retrieved, just to ensure    // that the caller only requests each chunk one at a time, in order.    int curChunk = 0;    StreamState(String appId, Iterator<ManagedBuffer> buffers) {      this.appId = appId;      this.buffers = Preconditions.checkNotNull(buffers);    }  }  public OneForOneStreamManager() {    // For debugging purposes, start with a random stream id to help identifying different streams.    // This does not need to be globally unique, only unique to this class.    nextStreamId = new AtomicLong((long) new Random().nextInt(Integer.MAX_VALUE) * 1000);    streams = new ConcurrentHashMap<>();  }  @Override  public void registerChannel(Channel channel, long streamId) {    if (streams.containsKey(streamId)) {      streams.get(streamId).associatedChannel = channel;    }  }  @Override  public ManagedBuffer getChunk(long streamId, int chunkIndex) {    StreamState state = streams.get(streamId);    if (chunkIndex != state.curChunk) {      throw new IllegalStateException(String.format(        "Received out-of-order chunk index %s (expected %s)", chunkIndex, state.curChunk));    } else if (!state.buffers.hasNext()) {      throw new IllegalStateException(String.format(        "Requested chunk index beyond end %s", chunkIndex));    }    state.curChunk += 1;    ManagedBuffer nextChunk = state.buffers.next();    if (!state.buffers.hasNext()) {      logger.trace("Removing stream id {}", streamId);      streams.remove(streamId);    }    return nextChunk;  }  @Override  public void connectionTerminated(Channel channel) {    // Close all streams which have been associated with the channel.    for (Map.Entry<Long, StreamState> entry: streams.entrySet()) {      StreamState state = entry.getValue();      if (state.associatedChannel == channel) {        streams.remove(entry.getKey());        // Release all remaining buffers.        while (state.buffers.hasNext()) {          state.buffers.next().release();        }      }    }  }  @Override  public void checkAuthorization(TransportClient client, long streamId) {    if (client.getClientId() != null) {      StreamState state = streams.get(streamId);      Preconditions.checkArgument(state != null, "Unknown stream ID.");      if (!client.getClientId().equals(state.appId)) {        throw new SecurityException(String.format(          "Client %s not authorized to read stream %d (app %s).",          client.getClientId(),          streamId,          state.appId));      }    }  }  /**   * Registers a stream of ManagedBuffers which are served as individual chunks one at a time to   * callers. Each ManagedBuffer will be release()'d after it is transferred on the wire. If a   * client connection is closed before the iterator is fully drained, then the remaining buffers   * will all be release()'d.   *   * If an app ID is provided, only callers who've authenticated with the given app ID will be   * allowed to fetch from this stream.   */  public long registerStream(String appId, Iterator<ManagedBuffer> buffers) {    long myStreamId = nextStreamId.getAndIncrement();    streams.put(myStreamId, new StreamState(appId, buffers));    return myStreamId;  }}