org.apache.beam.runners.core.metrics.MetricsMap.java Source code

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Here is the source code for org.apache.beam.runners.core.metrics.MetricsMap.java

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/*
 * 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.core.metrics;

import com.google.common.base.MoreObjects;
import com.google.common.collect.Iterables;
import java.io.Serializable;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import javax.annotation.Nullable;
import org.apache.beam.sdk.annotations.Experimental;
import org.apache.beam.sdk.annotations.Experimental.Kind;

/**
 * A map from {@code K} to {@code T} that supports getting or creating values associated with a key
 * in a thread-safe manner.
 */
@Experimental(Kind.METRICS)
public class MetricsMap<K, T> implements Serializable {

    /** Interface for creating instances to populate the {@link MetricsMap}. */
    public interface Factory<K, T> extends Serializable {
        /**
         * Create an instance of {@code T} to use with the given {@code key}.
         *
         * <p>It must be safe to call this from multiple threads.
         */
        T createInstance(K key);
    }

    private final Factory<K, T> factory;
    private final ConcurrentMap<K, T> metrics = new ConcurrentHashMap<>();

    public MetricsMap(Factory<K, T> factory) {
        this.factory = factory;
    }

    /**
     * Get or create the value associated with the given key.
     */
    public T get(K key) {
        T metric = metrics.get(key);
        if (metric == null) {
            metric = factory.createInstance(key);
            metric = MoreObjects.firstNonNull(metrics.putIfAbsent(key, metric), metric);
        }
        return metric;
    }

    /**
     * Get the value associated with the given key, if it exists.
     */
    @Nullable
    public T tryGet(K key) {
        return metrics.get(key);
    }

    /**
     * Return an iterable over the entries in the current {@link  MetricsMap}.
     */
    public Iterable<Map.Entry<K, T>> entries() {
        return Iterables.unmodifiableIterable(metrics.entrySet());
    }

    /**
     * Return an iterable over the values in the current {@link MetricsMap}.
     */
    public Iterable<T> values() {
        return Iterables.unmodifiableIterable(metrics.values());
    }
}