Use mach_absolute_time for HighResTimeStamp on Apple platforms

packages/react-native/React/Fabric/RCTConversions.h

@@ -21,18 +21,13 @@ NS_ASSUME_NONNULL_BEGIN
  * Converts an iOS timestamp (seconds since boot, NOT including sleep time, from
  * NSProcessInfo.processInfo.systemUptime or UITouch.timestamp) to a HighResTimeStamp.
  *
- * iOS timestamps use mach_absolute_time() which doesn't account for sleep time,
- * while std::chrono::steady_clock uses mach_continuous_time() which does.
- * To handle this correctly, we compute the relative offset from the current time
- * and apply it to HighResTimeStamp::now().
+ * iOS timestamps and HighResTimeStamp both use mach_absolute_time() which doesn't
+ * account for sleep time. We convert the timestamp directly since they share the
+ * same time domain.
  */
 inline facebook::react::HighResTimeStamp RCTHighResTimeStampFromSeconds(NSTimeInterval seconds)
 {
-  NSTimeInterval nowSystemUptime = NSProcessInfo.processInfo.systemUptime;
-  NSTimeInterval delta = nowSystemUptime - seconds;
-  auto deltaDuration =
-      std::chrono::duration_cast<std::chrono::steady_clock::duration>(std::chrono::duration<double>(delta));
-  return facebook::react::HighResTimeStamp::now() - facebook::react::HighResDuration::fromChrono(deltaDuration);
+  return facebook::react::HighResTimeStamp::fromDOMHighResTimeStamp(seconds * 1e3);
 }
 
 inline NSString *RCTNSStringFromString(

packages/react-native/ReactCommon/react/timing/__docs__/README.md

@@ -52,6 +52,23 @@ C++'s type system and the performance characteristics of native code. The
 implementation uses `std::chrono` internally but provides a more specialized
 interface tailored to React Native's needs.
 
+### Platform-Specific Clock Sources
+
+On different platforms, `HighResTimeStamp` uses different underlying clock
+sources to ensure compatibility with platform-specific timing APIs:
+
+- **iOS/macOS**: Uses `mach_absolute_time()`, which measures time since device
+  boot and **excludes sleep time**. This ensures compatibility with iOS system
+  APIs (like `UITouch.timestamp` and `NSProcessInfo.processInfo.systemUptime`)
+  and native performance logging systems that use the same clock source.
+
+- **Other platforms**: Uses `std::chrono::steady_clock`, which provides a
+  monotonic clock that may include or exclude sleep time depending on the
+  platform.
+
+This design ensures that timestamps recorded in JavaScript and passed to native
+systems will have correct timing on all platforms.
+
 ### HighResTimeStamp
 
 This class represents a specific point in time with high precision. It

packages/react-native/ReactCommon/react/timing/primitives.h

@@ -11,6 +11,10 @@
 #include <chrono>
 #include <functional>
 
+#ifdef __APPLE__
+#include <mach/mach_time.h>
+#endif
+
 namespace facebook::react {
 
 class HighResDuration;
@@ -312,6 +316,23 @@ class HighResTimeStamp {
     return HighResDuration(systemNow.time_since_epoch() - steadyNow.time_since_epoch());
   }
 
+#ifdef __APPLE__
+  static double getMachTimebaseConversionFactor()
+  {
+    mach_timebase_info_data_t info;
+    mach_timebase_info(&info);
+    return static_cast<double>(info.numer) / info.denom;
+  }
+
+  static std::chrono::steady_clock::time_point machAbsoluteTimeToSteadyClockTimePoint()
+  {
+    static double conversionFactor = getMachTimebaseConversionFactor();
+    uint64_t machTime = mach_absolute_time();
+    auto nanoseconds = static_cast<int64_t>(static_cast<double>(machTime) * conversionFactor);
+    return std::chrono::steady_clock::time_point(std::chrono::nanoseconds(nanoseconds));
+  }
+#endif
+
 #ifdef REACT_NATIVE_DEBUG
   static std::function<std::chrono::steady_clock::time_point()> &getTimeStampProvider()
   {
@@ -322,12 +343,23 @@ class HighResTimeStamp {
   static std::chrono::steady_clock::time_point chronoNow()
   {
     auto &timeStampProvider = getTimeStampProvider();
-    return timeStampProvider != nullptr ? timeStampProvider() : std::chrono::steady_clock::now();
+    if (timeStampProvider != nullptr) {
+      return timeStampProvider();
+    }
+#ifdef __APPLE__
+    return machAbsoluteTimeToSteadyClockTimePoint();
+#else
+    return std::chrono::steady_clock::now();
+#endif
   }
 #else
   inline static std::chrono::steady_clock::time_point chronoNow()
   {
+#ifdef __APPLE__
+    return machAbsoluteTimeToSteadyClockTimePoint();
+#else
     return std::chrono::steady_clock::now();
+#endif
   }
 #endif
 };