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Apache Hadoop Common

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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.hadoop.metrics2.lib;

import java.util.concurrent.atomic.AtomicInteger;

import org.apache.hadoop.metrics2.MetricsInfo;
import org.apache.hadoop.metrics2.MetricsRecordBuilder;

/**
 * A mutable float gauge.
 */
public class MutableGaugeFloat extends MutableGauge {

  private AtomicInteger value = new AtomicInteger();

  MutableGaugeFloat(MetricsInfo info, float initValue) {
    super(info);
    this.value.set(Float.floatToIntBits(initValue));
  }

  public float value() {
    return Float.intBitsToFloat(value.get());
  }

  @Override
  public void incr() {
    incr(1.0f);
  }

  @Override
  public void decr() {
    incr(-1.0f);
  }

  @Override
  public void snapshot(MetricsRecordBuilder builder, boolean all) {
    if (all || changed()) {
      builder.addGauge(info(), value());
      clearChanged();
    }
  }

  public void set(float value) {
    this.value.set(Float.floatToIntBits(value));
    setChanged();
  }

  private final boolean compareAndSet(float expect, float update) {
    return value.compareAndSet(Float.floatToIntBits(expect),
        Float.floatToIntBits(update));
  }

  private void incr(float delta) {
    while (true) {
      float current = value.get();
      float next = current + delta;
      if (compareAndSet(current, next)) {
        setChanged();
        return;
      }
    }
  }

  /**
   * @return  the value of the metric
   */
  public String toString() {
    return value.toString();
  }
}