From dc898cc5d8d62ebc3505e5248a2e9b017db216ce Mon Sep 17 00:00:00 2001
From: Nick Lefever <lefever@meta.com>
Date: Wed, 9 Apr 2025 04:53:23 -0700
Subject: [PATCH] Add high resolution CPU time support on macOS (#50553)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/50553

Adding nanosecond resolution for macOS to the NativeCPUTime native module. This allows for running Fantom benchmarks on macOS with high resolution CPUTime counters.

This change adds the internal `getCPUTimeConversionFactor` function which is needed to convert the output from `mach_absolute_time` to a double representing time in nanoseconds. The native module calls `getCPUTTimeConversionFactor` once in the constructor and stores the result for future calls. The conversion factor defaults to 1.0 for all other platforms.

Changelog: [internal]

Reviewed By: rubennorte

Differential Revision: D72631963

fbshipit-source-id: 33fa1bfc576e634187091bfa668106e31cc62214
---
 .../react/nativemodule/cputime/CPUTime.h      | 32 +++++++++++++++++--
 1 file changed, 30 insertions(+), 2 deletions(-)

diff --git a/packages/react-native/ReactCommon/react/nativemodule/cputime/CPUTime.h b/packages/react-native/ReactCommon/react/nativemodule/cputime/CPUTime.h
index fe260ff03f2..fa78ed5e616 100644
--- a/packages/react-native/ReactCommon/react/nativemodule/cputime/CPUTime.h
+++ b/packages/react-native/ReactCommon/react/nativemodule/cputime/CPUTime.h
@@ -7,8 +7,10 @@
 
 #pragma once
 
-#ifdef USE_POSIX_TIME
+#if defined USE_POSIX_TIME
 #include <time.h>
+#elif defined __MACH__
+#include <mach/mach_time.h>
 #else
 #include <chrono>
 #endif
@@ -21,9 +23,23 @@ const double NANOSECONDS_IN_A_SECOND = 1000000000;
 
 #endif
 
+#ifdef __MACH__
+
+namespace {
+inline double getConversionFactor() {
+  double conversionFactor;
+  mach_timebase_info_data_t info;
+  mach_timebase_info(&info);
+  conversionFactor = static_cast<double>(info.numer) / info.denom;
+  return conversionFactor;
+}
+} // namespace
+
+#endif
+
 namespace facebook::react {
 
-#ifdef USE_POSIX_TIME
+#if defined USE_POSIX_TIME
 
 inline double getCPUTimeNanos() {
   struct timespec time {};
@@ -36,6 +52,18 @@ inline bool hasAccurateCPUTimeNanosForBenchmarks() {
   return true;
 }
 
+#elif defined __MACH__
+
+inline double getCPUTimeNanos() {
+  static auto conversionFactor = getConversionFactor();
+  uint64_t time = mach_absolute_time();
+  return static_cast<double>(time) * conversionFactor;
+}
+
+inline bool hasAccurateCPUTimeNanosForBenchmarks() {
+  return true;
+}
+
 #else
 
 inline double getCPUTimeNanos() {