react-native/ReactCommon/microprofiler/MicroProfiler.h

// Copyright 2004-present Facebook. All Rights Reserved.

#pragma once

#include <atomic>
#include <thread>

// #define WITH_MICRO_PROFILER 1

#ifdef WITH_MICRO_PROFILER
#define MICRO_PROFILER_SECTION(name) MicroProfilerSection __b(name)
#define MICRO_PROFILER_SECTION_NAMED(var_name, name) MicroProfilerSection var_name(name)
#else
#define MICRO_PROFILER_SECTION(name)
#define MICRO_PROFILER_SECTION_NAMED(var_name, name)
#endif

namespace facebook {
namespace react {

enum MicroProfilerName {
  __INTERNAL_BENCHMARK_INNER,
  __INTERNAL_BENCHMARK_OUTER,
  __LENGTH__,
};

/**
 * MicroProfiler is a performance profiler for measuring the cumulative impact of
 * a large number of small-ish calls. This is normally a problem for standard profilers
 * like Systrace because the overhead of the profiler itself skews the timings you
 * are able to collect. This is especially a problem when doing nested calls to
 * profiled functions, as the parent calls will contain the overhead of their profiling
 * plus the overhead of all their childrens' profiling.
 *
 * MicroProfiler attempts to be low overhead by 1) aggregating timings in memory and
 * 2) trying to remove estimated profiling overhead from the returned timings.
 *
 * To remove estimated overhead, at the beginning of each trace we calculate the
 * average cost of profiling a no-op code section, as well as invoking the average
 * cost of invoking the system clock. The former is subtracted out for each child
 * profiler section that is invoked within a parent profiler section. The latter is
 * subtracted from each section, child or not.
 *
 * After MicroProfiler::stopProfiling() is called, a table of tracing data is emitted
 * to glog (which shows up in logcat on Android).
 */
struct MicroProfiler {
  static const char* profilingNameToString(MicroProfilerName name) {
    switch (name) {
      case __INTERNAL_BENCHMARK_INNER:
        return "__INTERNAL_BENCHMARK_INNER";
      case __INTERNAL_BENCHMARK_OUTER:
        return "__INTERNAL_BENCHMARK_OUTER";
      case __LENGTH__:
        throw std::runtime_error("__LENGTH__ has no name");
      default:
        throw std::runtime_error("Trying to convert unknown MicroProfilerName to string");
    }
  }

  static void startProfiling();
  static void stopProfiling();
  static bool isProfiling();
  static void runInternalBenchmark();
};

class MicroProfilerSection {
public:
  MicroProfilerSection(MicroProfilerName name);
  ~MicroProfilerSection();

private:
  bool isProfiling_;
  MicroProfilerName name_;
  uint_fast64_t startTime_;
  uint_fast32_t startNumProfileSections_;
};

} }