com.github.sadikovi.spark.util.CloseableIterator.scala Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of spark-netflow_2.10 Show documentation
spark-netflow
The newest version!
/*
 * Copyright 2016 sadikovi
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.github.sadikovi.spark.util

/**
 * [[CloseableIterator]] provides ability to close associated resources once iteration is finished.
 * Copied from apache/spark and slightly modified version of `NextIterator`.
 */
private[spark] abstract class CloseableIterator[U] extends Iterator[U] {
  private var gotNext = false
  private var nextValue: U = _
  private var closed = false
  protected var finished = false

  /**
   * Method for subclasses to implement to provide the next element.
   *
   * If no next element is available, the subclass should set `finished`
   * to `true` and may return any value (it will be ignored).
   *
   * This convention is required because `null` may be a valid value,
   * and using `Option` seems like it might create unnecessary Some/None
   * instances, given some iterators might be called in a tight loop.
   *
   * @return U, or set 'finished' when done
   */
  protected def getNext(): U

  /**
   * Method for subclasses to implement when all elements have been successfully
   * iterated, and the iteration is done.
   *
   * Ideally you should have another try/catch that ensures any resources are closed should
   * iteration fail.
   */
  protected def close()

  /**
   * Calls the subclass-defined close method, but only once.
   *
   * Usually calling `close` multiple times should be fine, but historically
   * there have been issues with some InputFormats throwing exceptions.
   */
  def closeIfNeeded() {
    if (!closed) {
      // Note: it's important that we set closed = true before calling close(), since setting it
      // afterwards would permit us to call close() multiple times if close() threw an exception.
      closed = true
      close()
    }
  }

  override def hasNext: Boolean = {
    if (!finished) {
      if (!gotNext) {
        nextValue = getNext()
        if (finished) {
          closeIfNeeded()
        }
        gotNext = true
      }
    }
    !finished
  }

  override def next(): U = {
    if (!hasNext) {
      throw new NoSuchElementException("End of stream")
    }
    gotNext = false
    nextValue
  }
}