Shuffle Client Operations

/**
 * Abstract base class for clients that read shuffle files from executors or external services
 */
public abstract class ShuffleClient implements Closeable {
    /**
     * Initialize the client for the given application
     * @param appId - Application ID to initialize client for
     */
    public void init(String appId);
    
    /**
     * Fetch blocks from a remote shuffle service
     * @param host - Host name of the shuffle service
     * @param port - Port number of the shuffle service
     * @param execId - Executor ID
     * @param blockIds - Array of block IDs to fetch
     * @param listener - Listener for block fetch events
     * @param downloadFileManager - Manager for temporary download files, can be null
     */
    public abstract void fetchBlocks(
        String host, int port, String execId, String[] blockIds,
        BlockFetchingListener listener, DownloadFileManager downloadFileManager
    );
    
    /**
     * Get shuffle metrics for monitoring
     * @return MetricSet containing shuffle performance metrics
     */
    public MetricSet shuffleMetrics();
    
    /**
     * Close the client and clean up resources
     */
    public void close();
}

/**
 * Client implementation for reading shuffle blocks from external shuffle service
 */
public class ExternalShuffleClient extends ShuffleClient {
    /**
     * Create an external shuffle client
     * @param conf - Transport configuration
     * @param secretKeyHolder - Secret key holder for authentication
     * @param authEnabled - Whether authentication is enabled
     * @param registrationTimeoutMs - Timeout for registration operations in milliseconds
     */
    public ExternalShuffleClient(
        TransportConf conf, SecretKeyHolder secretKeyHolder,
        boolean authEnabled, long registrationTimeoutMs
    );
    
    /**
     * Initialize the client for the given application
     * @param appId - Application ID to initialize client for
     */
    @Override
    public void init(String appId);
    
    /**
     * Fetch blocks from the external shuffle service
     * @param host - Host name of the shuffle service
     * @param port - Port number of the shuffle service
     * @param execId - Executor ID
     * @param blockIds - Array of block IDs to fetch
     * @param listener - Listener for block fetch events
     * @param downloadFileManager - Manager for temporary download files, can be null
     */
    @Override
    public void fetchBlocks(
        String host, int port, String execId, String[] blockIds,
        BlockFetchingListener listener, DownloadFileManager downloadFileManager
    );
    
    /**
     * Get shuffle metrics for monitoring
     * @return MetricSet containing shuffle performance metrics
     */
    @Override
    public MetricSet shuffleMetrics();
    
    /**
     * Register an executor with the external shuffle service
     * @param host - Host name of the shuffle service
     * @param port - Port number of the shuffle service
     * @param execId - Executor ID to register
     * @param executorInfo - Information about the executor's shuffle configuration
     * @throws IOException if network communication fails
     * @throws InterruptedException if the operation is interrupted
     */
    public void registerWithShuffleServer(
        String host, int port, String execId, ExecutorShuffleInfo executorInfo
    ) throws IOException, InterruptedException;
    
    /**
     * Close the client and clean up resources
     */
    @Override
    public void close();
}

import org.apache.spark.network.shuffle.ExternalShuffleClient;
import org.apache.spark.network.shuffle.BlockFetchingListener;
import org.apache.spark.network.shuffle.protocol.ExecutorShuffleInfo;
import org.apache.spark.network.sasl.ShuffleSecretManager;
import org.apache.spark.network.util.TransportConf;

// Create transport configuration
TransportConf conf = new TransportConf("shuffle");

// Create secret manager for authentication
ShuffleSecretManager secretManager = new ShuffleSecretManager();
secretManager.registerApp("app1", "secretKey123");

// Create external shuffle client
ExternalShuffleClient client = new ExternalShuffleClient(conf, secretManager, true, 10000);

// Initialize for application
client.init("app1");

// Register executor with shuffle service
String[] localDirs = {"/tmp/spark-1", "/tmp/spark-2"};
ExecutorShuffleInfo executorInfo = new ExecutorShuffleInfo(localDirs, 64, "sort");
client.registerWithShuffleServer("shuffle-node-1", 7337, "executor-1", executorInfo);

// Create block fetching listener
BlockFetchingListener listener = new BlockFetchingListener() {
    @Override
    public void onBlockFetchSuccess(String blockId, ManagedBuffer data) {
        System.out.println("Successfully fetched block: " + blockId + 
                          ", size: " + data.size() + " bytes");
        // Process the block data
        try {
            // Convert to bytes and process
            byte[] blockData = ByteStreams.toByteArray(data.createInputStream());
            processBlockData(blockId, blockData);
        } catch (IOException e) {
            System.err.println("Error processing block data: " + e.getMessage());
        } finally {
            data.release(); // Important: release the buffer
        }
    }
    
    @Override
    public void onBlockFetchFailure(String blockId, Throwable exception) {
        System.err.println("Failed to fetch block: " + blockId + ", error: " + exception.getMessage());
        // Handle retry logic or error reporting
        handleBlockFetchFailure(blockId, exception);
    }
};

// Fetch specific blocks
String[] blockIds = {"shuffle_1_0_0", "shuffle_1_0_1", "shuffle_1_0_2"};
client.fetchBlocks("shuffle-node-1", 7337, "executor-1", blockIds, listener, null);

// Monitor shuffle metrics
MetricSet metrics = client.shuffleMetrics();
System.out.println("Shuffle metrics: " + metrics);

// Clean up when done
client.close();