google.registry.monitoring.metrics.VirtualMetric.java Source code

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Here is the source code for google.registry.monitoring.metrics.VirtualMetric.java

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// Copyright 2016 The Nomulus Authors. 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 google.registry.monitoring.metrics;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Supplier;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import google.registry.monitoring.metrics.MetricSchema.Kind;
import java.util.Map.Entry;
import javax.annotation.concurrent.ThreadSafe;
import org.joda.time.Instant;

/**
 * A metric whose value is computed at sample-time.
 *
 * <p>This pattern works well for gauge-like metrics, such as CPU usage, memory usage, and file
 * descriptor counts.
 *
 * <p>The {@link MetricPoint#interval()} of values of instances of this metric will always have a
 * start time equal to the end time, since the metric value represents a point-in-time snapshot with
 * no relationship to prior values.
 */
@ThreadSafe
public final class VirtualMetric<V> extends AbstractMetric<V> {

    private final Supplier<ImmutableMap<ImmutableList<String>, V>> valuesSupplier;

    /**
     * Local cache of the count of values so that we don't have to evaluate the callback function to
     * get the metric's cardinality.
     */
    private volatile int cardinality;

    VirtualMetric(String name, String description, String valueDisplayName, ImmutableSet<LabelDescriptor> labels,
            Supplier<ImmutableMap<ImmutableList<String>, V>> valuesSupplier, Class<V> valueClass) {
        super(name, description, valueDisplayName, Kind.GAUGE, labels, valueClass);

        this.valuesSupplier = valuesSupplier;
    }

    /**
     * Returns a snapshot of the metric's values. This will evaluate the stored callback function. The
     * timestamp for each MetricPoint will be the current time.
     */
    @Override
    public ImmutableList<MetricPoint<V>> getTimestampedValues() {
        return getTimestampedValues(Instant.now());
    }

    /**
     * Returns the cached value of the cardinality of this metric. The cardinality is computed when
     * the metric is evaluated. If the metric has never been evaluated, the cardinality is zero.
     */
    @Override
    public int getCardinality() {
        return cardinality;
    }

    @VisibleForTesting
    ImmutableList<MetricPoint<V>> getTimestampedValues(Instant timestamp) {
        ImmutableMap<ImmutableList<String>, V> values = valuesSupplier.get();

        ImmutableList.Builder<MetricPoint<V>> metricPoints = new ImmutableList.Builder<>();
        for (Entry<ImmutableList<String>, V> entry : values.entrySet()) {
            metricPoints.add(MetricPoint.create(this, entry.getKey(), timestamp, timestamp, entry.getValue()));
        }

        cardinality = values.size();
        return metricPoints.build();
    }
}