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Apache Jena Fuseki server Kafka connector
There is a newer version: 1.4.0
/*
 * 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.kafka.common.metrics;

import org.apache.kafka.common.Metric;
import org.apache.kafka.common.MetricName;
import org.apache.kafka.common.utils.Time;

public final class KafkaMetric implements Metric {

    private final MetricName metricName;
    private final Object lock;
    private final Time time;
    private final MetricValueProvider metricValueProvider;
    private volatile MetricConfig config;

    // public for testing
    /**
     * Create a metric to monitor an object that implements MetricValueProvider.
     * @param lock The lock used to prevent race condition
     * @param metricName The name of the metric
     * @param valueProvider The metric value provider associated with this metric
     * @param config The configuration of the metric
     * @param time The time instance to use with the metrics
     */
    public KafkaMetric(Object lock, MetricName metricName, MetricValueProvider valueProvider,
            MetricConfig config, Time time) {
        this.metricName = metricName;
        this.lock = lock;
        if (!(valueProvider instanceof Measurable) && !(valueProvider instanceof Gauge))
            throw new IllegalArgumentException("Unsupported metric value provider of class " + valueProvider.getClass());
        this.metricValueProvider = valueProvider;
        this.config = config;
        this.time = time;
    }

    /**
     * Get the configuration of this metric.
     * This is supposed to be used by server only.
     * @return Return the config of this metric
     */
    public MetricConfig config() {
        return this.config;
    }

    /**
     * Get the metric name
     * @return Return the name of this metric
     */
    @Override
    public MetricName metricName() {
        return this.metricName;
    }

    /**
     * Take the metric and return the value, which could be a {@link Measurable} or a {@link Gauge}
     * @return Return the metric value
     * @throws IllegalStateException if the underlying metric is not a {@link Measurable} or a {@link Gauge}.
     */
    @Override
    public Object metricValue() {
        long now = time.milliseconds();
        synchronized (this.lock) {
            if (isMeasurable())
                return ((Measurable) metricValueProvider).measure(config, now);
            else if (this.metricValueProvider instanceof Gauge)
                return ((Gauge) metricValueProvider).value(config, now);
            else
                throw new IllegalStateException("Not a valid metric: " + this.metricValueProvider.getClass());
        }
    }

    /**
     * The method determines if the metric value provider is of type Measurable.
     *
     * @return true if the metric value provider is of type Measurable, false otherwise.
     */
    public boolean isMeasurable() {
        return this.metricValueProvider instanceof Measurable;
    }

    /**
     * Get the underlying metric provider, which should be a {@link Measurable}
     * @return Return the metric provider
     * @throws IllegalStateException if the underlying metric is not a {@link Measurable}.
     */
    public Measurable measurable() {
        if (isMeasurable())
            return (Measurable) metricValueProvider;
        else
            throw new IllegalStateException("Not a measurable: " + this.metricValueProvider.getClass());
    }

    /**
     * Take the metric and return the value, where the underlying metric provider should be a {@link Measurable}
     * @param timeMs The time that this metric is taken
     * @return Return the metric value if it's measurable, otherwise 0
     */
    double measurableValue(long timeMs) {
        synchronized (this.lock) {
            if (isMeasurable())
                return ((Measurable) metricValueProvider).measure(config, timeMs);
            else
                return 0;
        }
    }

    /**
     * Set the metric config.
     * This is supposed to be used by server only.
     * @param config configuration for this metrics
     */
    public void config(MetricConfig config) {
        synchronized (lock) {
            this.config = config;
        }
    }
}