content: /*
   * 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 com.alibaba.metrics;
  
  import java.io.Closeable;
  import java.util.concurrent.Callable;
  import java.util.concurrent.TimeUnit;
  
  /**
   * A timer metric which aggregates timing durations and provides duration statistics, plus
   * throughput statistics via {@link Meter}.
   * Timer相当于Meter+Histogram的组合，同时统计一段代码，一个方法的qps，以及执行时间的分布情况
   */
  public interface Timer extends Metered, Sampling {
      /**
       * A timing context.
       *
       * @see Timer#time()
       */
      interface Context extends Closeable {
  
          /**
           * Updates the timer with the difference between current and start time. Call to this method will
           * not reset the start time. Multiple calls result in multiple updates.
           * @return the elapsed time in nanoseconds
           */
          long stop();
      }
  
  
      /**
       * Adds a recorded duration.
       *
       * @param duration the length of the duration
       * @param unit     the scale unit of {@code duration}
       */
      void update(long duration, TimeUnit unit);
  
      /**
       * Times and records the duration of event.
       *
       * @param event a {@link Callable} whose {@link Callable#call()} method implements a process
       *              whose duration should be timed
       * @param <T>   the type of the value returned by {@code event}
       * @return the value returned by {@code event}
       * @throws Exception if {@code event} throws an {@link Exception}
       */
      <T> T time(Callable<T> event) throws Exception;
  
      /**
       * Returns a new {@link Context}.
       *
       * @return a new {@link Context}
       * @see Context
       */
      Context time();
  
  
  }
  