Spark2.0 shuffle service

Spark 的shuffle 服务是spark的核心，本文介绍了非ExternalShuffleClient的方式，看BlockService的整个架构。ShuffleClient是整个框架的基础，有init方法和fetchBlock两个方法。

/** Provides an interface for reading shuffle files, either from an Executor or external service. */  
public abstract class ShuffleClient implements Closeable {  
  
  /**  
   * Initializes the ShuffleClient, specifying this Executor's appId.  
   * Must be called before any other method on the ShuffleClient.  
   * 初始化ShuffleClient, 传入本执行器的程序ID，本方法必须在访问ShuffleClient的其它方法前调用。  
   */  
  public void init(String appId) { }  
  
  /**  
   * Fetch a sequence of blocks from a remote node asynchronously,  
   *  
   * Note that this API takes a sequence so the implementation can batch requests, and does not  
   * return a future so the underlying implementation can invoke onBlockFetchSuccess as soon as  
   * the data of a block is fetched, rather than waiting for all blocks to be fetched.  
   * 异步的从远程结点取一系列的数据块，并且不返回future对象，所以当取到一个数据块的数据时，底层的实现可以调用onBlockFetchSuccess方法，  
   * 并不用等所有的数据块都取完。  
   */  
  public abstract void fetchBlocks(  
      String host,  
      int port,  
      String execId,  
      String[] blockIds,  
      BlockFetchingListener listener);  
}  

BlockFetchingListener接口，onBlockFetchSuccess方法：每次成功取得一个数据块时调用。当本方法返回时，数据必须被自动释放。 如果数据被传递给另一个线程，接收者必须自己调用retain()和release()，或者拷贝数据到一个新的缓冲区。onBlockFetchFailure方法，数据块获取失败时，至少被调用一次。

public interface BlockFetchingListener extends EventListener {  
  /**  
   * Called once per successfully fetched block. After this call returns, data will be released  
   * automatically. If the data will be passed to another thread, the receiver should retain()  
   * and release() the buffer on their own, or copy the data to a new buffer.  
   */  
  void onBlockFetchSuccess(String blockId, ManagedBuffer data);  
  
  /**  
   * Called at least once per block upon failures.  
   */  
  void onBlockFetchFailure(String blockId, Throwable exception);  
}  

BlockTransferService扩展了ShuffleClient，有一些方法的公共的实现。

private[spark]  
abstract class BlockTransferService extends ShuffleClient with Closeable with Logging {  
  
  /**  
   * Initialize the transfer service by giving it the BlockDataManager that can be used to fetch  
   * local blocks or put local blocks.  
   * 通过传递给他BlockDataManager对象来初始化传输服务，BlockDataManager可以用来存取本地数据块。  
   */  
  def init(blockDataManager: BlockDataManager): Unit  
  
  /**  
   * Tear down the transfer service.  
   * 关闭传输服务。  
   */  
  def close(): Unit  
  
  /**  
   * Port number the service is listening on, available only after [[init]] is invoked.  
   * 传输服务所在的端口号，在调用init方法后可用。  
   */  
  def port: Int  
  
  /**  
   * Host name the service is listening on, available only after [[init]] is invoked.  
   * 传输服务所在的主机名，在调用init方法后可用。  
   */  
  def hostName: String  
  
  /**  
   * Fetch a sequence of blocks from a remote node asynchronously,  
   * available only after [[init]] is invoked.  
   *  
   * Note that this API takes a sequence so the implementation can batch requests, and does not  
   * return a future so the underlying implementation can invoke onBlockFetchSuccess as soon as  
   * the data of a block is fetched, rather than waiting for all blocks to be fetched.  
   *   
   * 异步的从远程结点取一系列的数据块，，仅在调用init方法后可用。  
   * 注意本API用一个序列，所以实现可以使用批量请求，并且不返回future对象，所以当取到一个数据块的数据时，底层的实现可以调用onBlockFetchSuccess方法，  
   * 并不用等所有的数据块都取完。  
 */ 

override def fetchBlocks( host: String, port: Int, execId: String, blockIds: Array[String], listener: BlockFetchingListener): Unit 

/**
　 * Upload a single block to a remote node, available only after [[init]] is invoked.  
   * 上传一个数据块到远程结点，仅在调用init方法后可用。  
   */  
  def uploadBlock(  
      hostname: String,  
      port: Int,  
      execId: String,  
      blockId: BlockId,  
      blockData: ManagedBuffer,  
      level: StorageLevel,  
      classTag: ClassTag[_]): Future[Unit]  
  
  /**  
   * A special case of [[fetchBlocks]], as it fetches only one block and is blocking.  
   *  
   * It is also only available after [[init]] is invoked.  
   * fetchBlocks的一个特别方法，他只取一个数据块并且阻塞，仅在调用init方法后可用。  
。  
   */  
  def fetchBlockSync(host: String, port: Int, execId: String, blockId: String): ManagedBuffer = {  
    // A monitor for the thread to wait on.  
    val result = Promise[ManagedBuffer]()  
    fetchBlocks(host, port, execId, Array(blockId),  
      new BlockFetchingListener {  
        override def onBlockFetchFailure(blockId: String, exception: Throwable): Unit = {  
          result.failure(exception)  
        }  
        override def onBlockFetchSuccess(blockId: String, data: ManagedBuffer): Unit = {  
          val ret = ByteBuffer.allocate(data.size.toInt)  
          ret.put(data.nioByteBuffer())  
          ret.flip()  
          result.success(new NioManagedBuffer(ret))  
        }  
      })  
    ThreadUtils.awaitResult(result.future, Duration.Inf)  
  }  
  
  /**  
   * Upload a single block to a remote node, available only after [[init]] is invoked.  
   *  
   * This method is similar to [[uploadBlock]], except this one blocks the thread  
   * until the upload finishes.  
   * 上传一个数据块到远程结点，仅在调用init方法后可用。  
   * 这个方法和uploadBlock方法类似，除了直到上传结点，本方法会一直阻塞。  
   */  
  def uploadBlockSync(  
      hostname: String,  
      port: Int,  
      execId: String,  
      blockId: BlockId,  
      blockData: ManagedBuffer,  
      level: StorageLevel,  
      classTag: ClassTag[_]): Unit = {  
    val future = uploadBlock(hostname, port, execId, blockId, blockData, level, classTag)  
    ThreadUtils.awaitResult(future, Duration.Inf)  
  }  
}  

NettyBlockTransferService扩展了BlockTransferServie