/*

  * 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.giraph.function;

 import org.apache.giraph.function.vertex.ConsumerWithVertex;

 import org.apache.giraph.function.vertex.SupplierFromVertex;

 import org.apache.giraph.graph.Vertex;

 import org.apache.hadoop.io.Writable;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Default object transfer, intermediary between producers and consumers.

  *

  * Holds value temporarily in memory, so can be used only when producer and

  * consumer are in the same context. Nulls it out after supplying, so each

  * object is returned only once, and second consecutive call to 'get' will

  * return null.

  *

  * Useful for both:

  *

  * - passing data from vertexReceive function of WorkerReceivePiece of previous

  * Piece to vertexSend function WorkerSendPiece of next Piece, of the same

  * vertex.

  * - when value is set on the master, and later read in block logic

  * (RepeatUntilBlock), or in a different Piece, either on worker or master.

  * If it is read within the same piece - just use local field.

  *

  * @param <T> Type of object to transfer.

  */

 public class ObjectTransfer<T> implements Supplier<T>, Consumer<T> {

   /** value */

   private T value;

   /**

    * Constructor

    * @param value initial value

    */

   public ObjectTransfer(T value) {

     this.value = value;

   }

   /** Constructor */

   public ObjectTransfer() {

   }

   @Override

   public T get() {

     T result = value;

     value = null;

     return result;

   }

   @Override

   public void apply(T value) {

     this.value = value;

   }

   @Override

   public String toString() {

     return getClass() + " [value=" + value + "]";

   }

   /**

    * To be called when needing to pass it as a Supplier - making it

    * obvious that K, V and E on supplier side can be any types,

    * and to make code work without compile errors/warnings.

    *

    * In Java7, some callsites might need explicit types:

    * object.<LongWritable, DoubleWritable, Writable>castToSupplier()

    * In Java8, object.castToSupplier() is always going to be enough.

    *

    * @param <I> Vertex id type

    * @param <V> Vertex value type

    * @param <E> Edge value type

    * @return supplier from vertex

    */

   // TODO Java8: cleanup callers

   @SuppressWarnings("rawtypes")

   public <I extends WritableComparable, V extends Writable, E extends Writable>

   SupplierFromVertex<I, V, E, T> castToSupplier() {

     return new SupplierFromVertex<I, V, E, T>() {

       @Override

       public T get(Vertex<I, V, E> vertex) {

         return ObjectTransfer.this.get();

       }

     };

   }

   /**

    * To be called when needing to pass it as a Consumer - making it

    * obvious that K, V and E on consumer side can be any types,

    * and to make code work without compile errors/warnings.

    *

    * In Java7, some callsites might need explicit types:

    * object.<LongWritable, DoubleWritable, Writable>castToConsumer()

    * In Java8, object.castToConsumer() is always going to be enough.

    *

    * @param <I> Vertex id type

    * @param <V> Vertex value type

    * @param <E> Edge value type

    * @return consumer with vertex

    */

   // TODO Java8: cleanup callers

   @SuppressWarnings("rawtypes")

   public <I extends WritableComparable, V extends Writable, E extends Writable>

   ConsumerWithVertex<I, V, E, T> castToConsumer() {

     return new ConsumerWithVertex<I, V, E, T>() {

       @Override

       public void apply(Vertex<I, V, E> vertex, T value) {

         ObjectTransfer.this.apply(value);

       }

     };

   }

 }