/**
* 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.mahout.cf.taste.hadoop.als;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;
/**
* Mapper class to be used by {@link MultithreadedSharingMapper}. Offers "global" before() and after() methods
* that will typically be used to set up static variables.
*
* Suitable for mappers that need large, read-only in-memory data to operate.
*
* @param <K1>
* @param <V1>
* @param <K2>
* @param <V2>
*/
public abstract class SharingMapper<K1,V1,K2,V2,S> extends Mapper<K1,V1,K2,V2> {
private static Object SHARED_INSTANCE;
/**
* Called before the multithreaded execution
*
* @param context mapper's context
*/
abstract S createSharedInstance(Context context) throws IOException;
final void setupSharedInstance(Context context) throws IOException {
if (SHARED_INSTANCE == null) {
SHARED_INSTANCE = createSharedInstance(context);
}
}
final S getSharedInstance() {
return (S) SHARED_INSTANCE;
}
static void reset() {
SHARED_INSTANCE = null;
}
}