core/src/main/scala/org/apache/spark/InterruptibleIterator.scala

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.spark

import org.apache.spark.annotation.DeveloperApi

/**
 * :: DeveloperApi ::
 * An iterator that wraps around an existing iterator to provide task killing functionality.
 * It works by checking the interrupted flag in [[TaskContext]].
 */
@DeveloperApi
class InterruptibleIterator[+T](val context: TaskContext, val delegate: Iterator[T])
  extends Iterator[T] {

  def hasNext: Boolean = {
    // TODO(aarondav/rxin): Check Thread.interrupted instead of context.interrupted if interrupt
    // is allowed. The assumption is that Thread.interrupted does not have a memory fence in read
    // (just a volatile field in C), while context.interrupted is a volatile in the JVM, which
    // introduces an expensive read fence.
    context.killTaskIfInterrupted()
    delegate.hasNext
  }

  def next(): T = delegate.next()
}