heron/api/src/java/com/twitter/heron/api/metric/MultiReducedMetric.java

// Copyright 2016 Twitter. All rights reserved.
//
// 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.twitter.heron.api.metric;

import java.util.HashMap;
import java.util.Map;

/*
 * A reduce metric that can hold multiple scoped values.
 * @param <T> accumulator to hold and update state
 * @param <U> type of input that can be handled
 * @param <V> type of reduced value
 */
public class MultiReducedMetric<T, U, V> implements IMetric<Map<String, V>> {
  private Map<String, ReducedMetric<T, U, V>> value = new HashMap<>();
  private IReducer<T, U, V> reducer;

  public MultiReducedMetric(IReducer<T, U, V> reducer) {
    this.reducer = reducer;
  }

  public ReducedMetric<T, U, V> scope(String key) {
    if (value.get(key) == null) {
      value.put(key, new ReducedMetric<>(reducer));
    }
    return value.get(key);
  }

  @Override
  public Map<String, V> getValueAndReset() {
    Map<String, V> ret = new HashMap<>();
    for (String key : value.keySet()) {
      V val = value.get(key).getValueAndReset();
      if (val != null) {
        ret.put(key, val);
      }
    }
    return ret;
  }
}