com.spotify.scio.util.FunctionsWithSideOutput.scala Maven / Gradle / Ivy

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Scio - A Scala API for Apache Beam and Google Cloud Dataflow

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/*
 * Copyright 2016 Spotify AB.
 *
 * 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.spotify.scio.util

import com.google.cloud.dataflow.sdk.transforms.DoFn
import com.spotify.scio.values.SideOutputContext

private[scio] object FunctionsWithSideOutput {

  trait SideOutputFn[T, U] extends DoFn[T, U] {
    private var ctx: SideOutputContext[T] = null
    def sideOutputContext(c: DoFn[T, U]#ProcessContext): SideOutputContext[T] = {
      if (ctx == null) {
        // Workaround for type inference limit
        ctx = new SideOutputContext(c.asInstanceOf[DoFn[T, AnyRef]#ProcessContext])
      }
      ctx
    }
  }

  def mapFn[T, U](f: (T, SideOutputContext[T]) => U): DoFn[T, U] = new SideOutputFn[T, U] {
    val g = ClosureCleaner(f)  // defeat closure
    override def processElement(c: DoFn[T, U]#ProcessContext): Unit = {
      c.output(g(c.element(), sideOutputContext(c)))
    }
  }

  def flatMapFn[T, U](f: (T, SideOutputContext[T]) => TraversableOnce[U])
  : DoFn[T, U] = new SideOutputFn[T, U] {
    val g = ClosureCleaner(f)  // defeat closure
    override def processElement(c: DoFn[T, U]#ProcessContext): Unit = {
      g(c.element(), sideOutputContext(c)).foreach(c.output)
    }
  }

}