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 org.apache.calcite.util.trace;
  
  import org.apache.calcite.util.NumberUtil;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  import org.slf4j.Logger;
  
  import java.text.DecimalFormat;
  
  /**
   * CalciteTimingTracer provides a mechanism for tracing the timing of a call
   * sequence at nanosecond resolution.
   */
  public class CalciteTimingTracer {
    //~ Static fields/initializers ---------------------------------------------
  
    private static final DecimalFormat DECIMAL_FORMAT =
        NumberUtil.decimalFormat("###,###,###,###,###");
  
    //~ Instance fields --------------------------------------------------------
  
    private final @Nullable Logger logger;
  
    private long lastNanoTime;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a new timing tracer, publishing an initial event (at elapsed time
     * 0).
     *
     * @param logger     logger on which to log timing events; level FINE will be
     *                   used
     * @param startEvent event to trace as start of timing
     */
    public CalciteTimingTracer(
        Logger logger,
        String startEvent) {
      if (!logger.isDebugEnabled()) {
        this.logger = null;
        return;
      } else {
        this.logger = logger;
      }
      lastNanoTime = System.nanoTime();
      logger.debug("{}:  elapsed nanos=0", startEvent);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    /**
     * Publishes an event with the time elapsed since the previous event.
     *
     * @param event event to trace
     */
    public void traceTime(String event) {
      if (logger == null) {
        return;
      }
      long newNanoTime = System.nanoTime();
      long elapsed = newNanoTime - lastNanoTime;
      lastNanoTime = newNanoTime;
      logger.debug("{}:  elapsed nanos={}", event, DECIMAL_FORMAT.format(elapsed));
    }
  }
  