text: //  Copyright (c) 2013, Facebook, Inc.  All rights reserved.
  //  This source code is licensed under the BSD-style license found in the
  //  LICENSE file in the root directory of this source tree. An additional grant
  //  of patent rights can be found in the PATENTS file in the same directory.
  //
  #pragma once
  #include "rocksdb/perf_context.h"
  #include "util/perf_step_timer.h"
  #include "util/stop_watch.h"
  
  namespace rocksdb {
  
  #if defined(NPERF_CONTEXT) || defined(IOS_CROSS_COMPILE)
  
  #define PERF_TIMER_GUARD(metric)
  #define PERF_TIMER_MEASURE(metric)
  #define PERF_TIMER_STOP(metric)
  #define PERF_TIMER_START(metric)
  #define PERF_COUNTER_ADD(metric, value)
  
  #else
  
  // Stop the timer and update the metric
  #define PERF_TIMER_STOP(metric)          \
    perf_step_timer_ ## metric.Stop();
  
  #define PERF_TIMER_START(metric)          \
    perf_step_timer_ ## metric.Start();
  
  // Declare and set start time of the timer
  #define PERF_TIMER_GUARD(metric)                                      \
    PerfStepTimer perf_step_timer_ ## metric(&(perf_context.metric));   \
    perf_step_timer_ ## metric.Start();
  
  // Update metric with time elapsed since last START. start time is reset
  // to current timestamp.
  #define PERF_TIMER_MEASURE(metric)        \
    perf_step_timer_ ## metric.Measure();
  
  // Increase metric value
  #define PERF_COUNTER_ADD(metric, value)     \
    perf_context.metric += value;
  
  #endif
  
  }
  