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public interface Producer<K,V> extends Closeable {
  
  /**
   * Needs to be called before any of the other transaction methods. Assumes that 
   * the producertransaction.app.id is specified in the producer configuration.
   *
   * This method does the following:
   *   1. Ensures any transactions initiated by previous instances of the producer
   *      are committed or rolled back.
   *   2. Gets the internal producer id and epoch, used in all future transactional
   *      messages issued by the producer.
   *
   * @throws IllegalStateException if the appId for the producer is not set 
   *         in the configuration.
   */
  void initTransactions() throws IllegalStateException;
  
  /**
   * Should be called before the start of each new transaction. 
   *
   * @throws ProducerFencedException if another producer is with the same
   *         transaction.app.id is active. 
   */
  void beginTransaction() throws ProducerFencedException;
  
  /** 
   * Sends a list of consumed offsets to the consumer group coordinator, and also marks 
   * those offsets as part of the current transaction. These offsets will be considered 
   * consumed only if the transaction is committed successfully.
   *
   * This method should be used when you need to batch consumed and produced messages 
   * together, typically in a consume-transform-produce pattern.
   * 
   * @throws ProducerFencedException if another producer is with the same
   *         transaction.app.id is active. 
   */
  void sendOffsetsToTransaction(Map<TopicPartition, OffsetAndMetadata> offsets, 
                                String consumerGroupId) throws ProducerFencedException;
  
  /**
   * Commits the ongoing transaction. 
   *
   * @throws ProducerFencedException if another producer is with the same
   *         transaction.app.id is active. 
   */
  void commitTransaction() throws ProducerFencedException;
  
  /**
   * Aborts the ongoing transaction.
   *
   * @throws ProducerFencedException if another producer is with the same
   *         transaction.app.id is active. 


   */
  void abortTransaction() throws ProducerFencedException;


  /**
   * Send the given record asynchronously and return a future which will eventually contain the response information.
   *
   * @param record The record to send
   * @return A future which will eventually contain the response information
   *
   * @throws UnrecognizedMessageException if the broker detects data loss: ie. previous messages which we expect
   *         to be committed are detected to be missing. This is a fatal error.
   */
  public Future<RecordMetadata> send(ProducerRecord<K, V> record) throws UnrecognizedMessageException;


  /**
   * Send a record and invoke the given callback when the record has been acknowledged by the server
   *
   * @throws UnrecognizedMessageException if the broker detects data loss: ie. previous messages which we expect
   *         to be committed are detected to be missing. This is a fatal error.
   */
  public Future<RecordMetadata> send(ProducerRecord<K, V> record, Callback callback) throws UnrecognizedMessageException;
}