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Source code: Class Accumulator.scala part of spark-core_2.11 version 2.4.1

/*
 * 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

/**
 * A simpler value of [[Accumulable]] where the result type being accumulated is the same
 * as the types of elements being merged, i.e. variables that are only "added" to through an
 * associative and commutative operation and can therefore be efficiently supported in parallel.
 * They can be used to implement counters (as in MapReduce) or sums. Spark natively supports
 * accumulators of numeric value types, and programmers can add support for new types.
 *
 * An accumulator is created from an initial value `v` by calling `SparkContext.accumulator`.
 * Tasks running on the cluster can then add to it using the `+=` operator.
 * However, they cannot read its value. Only the driver program can read the accumulator's value,
 * using its [[#value]] method.
 *
 * The interpreter session below shows an accumulator being used to add up the elements of an array:
 *
 * {{{
 * scala> val accum = sc.accumulator(0)
 * accum: org.apache.spark.Accumulator[Int] = 0
 *
 * scala> sc.parallelize(Array(1, 2, 3, 4)).foreach(x => accum += x)
 * ...
 * 10/09/29 18:41:08 INFO SparkContext: Tasks finished in 0.317106 s
 *
 * scala> accum.value
 * res2: Int = 10
 * }}}
 *
 * @param initialValue initial value of accumulator
 * @param param helper object defining how to add elements of type `T`
 * @param name human-readable name associated with this accumulator
 * @param countFailedValues whether to accumulate values from failed tasks
 * @tparam T result type
*/
@deprecated("use AccumulatorV2", "2.0.0")
class Accumulator[T] private[spark] (
    // SI-8813: This must explicitly be a private val, or else scala 2.11 doesn't compile
    @transient private val initialValue: T,
    param: AccumulatorParam[T],
    name: Option[String] = None,
    countFailedValues: Boolean = false)
  extends Accumulable[T, T](initialValue, param, name, countFailedValues)


/**
 * A simpler version of [[org.apache.spark.AccumulableParam]] where the only data type you can add
 * in is the same type as the accumulated value. An implicit AccumulatorParam object needs to be
 * available when you create Accumulators of a specific type.
 *
 * @tparam T type of value to accumulate
 */
@deprecated("use AccumulatorV2", "2.0.0")
trait AccumulatorParam[T] extends AccumulableParam[T, T] {
  def addAccumulator(t1: T, t2: T): T = {
    addInPlace(t1, t2)
  }
}


@deprecated("use AccumulatorV2", "2.0.0")
object AccumulatorParam {

  // The following implicit objects were in SparkContext before 1.2 and users had to
  // `import SparkContext._` to enable them. Now we move them here to make the compiler find
  // them automatically. However, as there are duplicate codes in SparkContext for backward
  // compatibility, please update them accordingly if you modify the following implicit objects.

  @deprecated("use AccumulatorV2", "2.0.0")
  implicit object DoubleAccumulatorParam extends AccumulatorParam[Double] {
    def addInPlace(t1: Double, t2: Double): Double = t1 + t2
    def zero(initialValue: Double): Double = 0.0
  }

  @deprecated("use AccumulatorV2", "2.0.0")
  implicit object IntAccumulatorParam extends AccumulatorParam[Int] {
    def addInPlace(t1: Int, t2: Int): Int = t1 + t2
    def zero(initialValue: Int): Int = 0
  }

  @deprecated("use AccumulatorV2", "2.0.0")
  implicit object LongAccumulatorParam extends AccumulatorParam[Long] {
    def addInPlace(t1: Long, t2: Long): Long = t1 + t2
    def zero(initialValue: Long): Long = 0L
  }

  @deprecated("use AccumulatorV2", "2.0.0")
  implicit object FloatAccumulatorParam extends AccumulatorParam[Float] {
    def addInPlace(t1: Float, t2: Float): Float = t1 + t2
    def zero(initialValue: Float): Float = 0f
  }

  // Note: when merging values, this param just adopts the newer value. This is used only
  // internally for things that shouldn't really be accumulated across tasks, like input
  // read method, which should be the same across all tasks in the same stage.
  @deprecated("use AccumulatorV2", "2.0.0")
  private[spark] object StringAccumulatorParam extends AccumulatorParam[String] {
    def addInPlace(t1: String, t2: String): String = t2
    def zero(initialValue: String): String = ""
  }
}




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