BasicGauge.java

/**
 * Copyright 2013 Netflix, Inc.
 * <p/>
 * 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
 * <p/>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p/>
 * 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.netflix.servo.monitor;

import com.netflix.servo.annotations.DataSourceType;
import com.netflix.servo.util.Throwables;

import java.util.concurrent.Callable;

/**
 * A gauge implementation that invokes a specified callable to get the current value.
 */
public final class BasicGauge<T extends Number> extends AbstractMonitor<T> implements Gauge<T> {
  private final Callable<T> function;

  /**
   * Creates a new instance of the gauge.
   *
   * @param config   configuration for this monitor
   * @param function a function used to fetch the value on demand
   */
  public BasicGauge(MonitorConfig config, Callable<T> function) {
    super(config.withAdditionalTag(DataSourceType.GAUGE));
    this.function = function;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public T getValue(int pollerIndex) {
    try {
      return function.call();
    } catch (Exception e) {
      throw Throwables.propagate(e);
    }
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public boolean equals(Object obj) {
    if (obj == null || !(obj instanceof BasicGauge)) {
      return false;
    }
    BasicGauge m = (BasicGauge) obj;
    return config.equals(m.getConfig()) && function.equals(m.function);
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public int hashCode() {
    int result = config.hashCode();
    result = 31 * result + function.hashCode();
    return result;
  }

  /**
   * {@inheritDoc}
   */
  @Override
  public String toString() {
    return "BasicGauge{config=" + config + ", function=" + function + '}';
  }
}