content: /*
   * 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.beam.runners.dataflow.worker;
  
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicLong;
  import org.apache.beam.runners.core.metrics.CounterCell;
  import org.apache.beam.runners.core.metrics.DirtyState;
  import org.apache.beam.runners.core.metrics.MetricCell;
  import org.apache.beam.sdk.metrics.Counter;
  import org.apache.beam.sdk.metrics.MetricName;
  
  /**
   * Version of {@link CounterCell} supporting multi-thread safe mutations and extraction of delta
   * values. {@link RemoveSafeDeltaCounterCell} allows safe deletions from the underlying {@code
   * countersMap} through the {@code deleteIfZero} method.
   */
  public class RemoveSafeDeltaCounterCell implements Counter, MetricCell<Long> {
  
    private final MetricName metricName;
    /**
     * This class does not own {@code countersMap} and only operates on a single key in the map
     * specified by {@code metricName}. These opeations include the {@link Counter} interface along
     * with the {@code deleteIfZero} method.
     */
    private final ConcurrentHashMap<MetricName, AtomicLong> countersMap;
  
    /**
     * @param metricName Specifies which metric this counter refers to.
     * @param countersMap The underlying {@code map} used to store this metric.
     */
    public RemoveSafeDeltaCounterCell(
        MetricName metricName, ConcurrentHashMap<MetricName, AtomicLong> countersMap) {
      this.metricName = metricName;
      this.countersMap = countersMap;
    }
  
    @Override
    public void reset() {
      countersMap.computeIfPresent(
          metricName,
          (unusedName, value) -> {
            value.set(0);
            return value;
          });
    }
  
    @Override
    public void inc(long n) {
      AtomicLong val = countersMap.get(metricName);
      if (val != null) {
        val.getAndAdd(n);
        return;
      }
      countersMap.computeIfAbsent(metricName, name -> new AtomicLong()).getAndAdd(n);
    }
  
    @Override
    public void inc() {
      inc(1);
    }
  
    @Override
    public void dec() {
      inc(-1);
    }
  
    @Override
    public void dec(long n) {
      inc(-1 * n);
    }
  
    @Override
    public MetricName getName() {
      return metricName;
    }
  
    @Override
    public DirtyState getDirty() {
      throw new UnsupportedOperationException(
          String.format("%s doesn't support the getDirty", getClass().getSimpleName()));
    }
  
    @Override
    public Long getCumulative() {
      throw new UnsupportedOperationException("getCumulative is not supported by Streaming Metrics");
    }
  
    /** Remove the metric from the {@code countersMap} if the the metric is zero valued. */
    @SuppressWarnings(
        "nullness") // computeIfPresent's remapping function can return null to remove the entry.
    public void deleteIfZero() {
      countersMap.computeIfPresent(
          metricName,
          (name, value) -> {
            return value.get() == 0L ? null : value;
          });
    }
  }
  