4 files changed, 87 insertions, 51 deletions
diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc
index 0e65005b..f6e64242 100644
--- a/absl/base/internal/cycleclock.cc
+++ b/absl/base/internal/cycleclock.cc
@@ -25,6 +25,7 @@
 #include <atomic>
 #include <chrono>  // NOLINT(build/c++11)
 
+#include "absl/base/attributes.h"
 #include "absl/base/internal/unscaledcycleclock.h"
 
 namespace absl {
@@ -33,44 +34,18 @@ namespace base_internal {
 
 #if ABSL_USE_UNSCALED_CYCLECLOCK
 
-namespace {
+constexpr int32_t CycleClock::kShift;
+constexpr double CycleClock::kFrequencyScale;
 
-#ifdef NDEBUG
-#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
-// Not debug mode and the UnscaledCycleClock frequency is the CPU
-// frequency.  Scale the CycleClock to prevent overflow if someone
-// tries to represent the time as cycles since the Unix epoch.
-static constexpr int32_t kShift = 1;
-#else
-// Not debug mode and the UnscaledCycleClock isn't operating at the
-// raw CPU frequency. There is no need to do any scaling, so don't
-// needlessly sacrifice precision.
-static constexpr int32_t kShift = 0;
-#endif
-#else
-// In debug mode use a different shift to discourage depending on a
-// particular shift value.
-static constexpr int32_t kShift = 2;
-#endif
-
-static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
-static std::atomic<CycleClockSourceFunc> cycle_clock_source;
+ABSL_CONST_INIT std::atomic<CycleClockSourceFunc>
+    CycleClock::cycle_clock_source_{nullptr};
 
-CycleClockSourceFunc LoadCycleClockSource() {
-  // Optimize for the common case (no callback) by first doing a relaxed load;
-  // this is significantly faster on non-x86 platforms.
-  if (cycle_clock_source.load(std::memory_order_relaxed) == nullptr) {
-    return nullptr;
-  }
-  // This corresponds to the store(std::memory_order_release) in
-  // CycleClockSource::Register, and makes sure that any updates made prior to
-  // registering the callback are visible to this thread before the callback is
-  // invoked.
-  return cycle_clock_source.load(std::memory_order_acquire);
+void CycleClockSource::Register(CycleClockSourceFunc source) {
+  // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
+  CycleClock::cycle_clock_source_.store(source, std::memory_order_release);
 }
 
-}  // namespace
-
+#ifdef _WIN32
 int64_t CycleClock::Now() {
   auto fn = LoadCycleClockSource();
   if (fn == nullptr) {
@@ -78,15 +53,7 @@ int64_t CycleClock::Now() {
   }
   return fn() >> kShift;
 }
-
-double CycleClock::Frequency() {
-  return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
-}
-
-void CycleClockSource::Register(CycleClockSourceFunc source) {
-  // Corresponds to the load(std::memory_order_acquire) in LoadCycleClockSource.
-  cycle_clock_source.store(source, std::memory_order_release);
-}
+#endif
 
 #else
 
diff --git a/absl/base/internal/cycleclock.h b/absl/base/internal/cycleclock.h
index a18b5844..9704e388 100644
--- a/absl/base/internal/cycleclock.h
+++ b/absl/base/internal/cycleclock.h
@@ -42,14 +42,19 @@
 #ifndef ABSL_BASE_INTERNAL_CYCLECLOCK_H_
 #define ABSL_BASE_INTERNAL_CYCLECLOCK_H_
 
+#include <atomic>
 #include <cstdint>
 
+#include "absl/base/attributes.h"
 #include "absl/base/config.h"
+#include "absl/base/internal/unscaledcycleclock.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 
+using CycleClockSourceFunc = int64_t (*)();
+
 // -----------------------------------------------------------------------------
 // CycleClock
 // -----------------------------------------------------------------------------
@@ -68,12 +73,37 @@ class CycleClock {
   static double Frequency();
 
  private:
+#if ABSL_USE_UNSCALED_CYCLECLOCK
+  static CycleClockSourceFunc LoadCycleClockSource();
+
+#ifdef NDEBUG
+#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+  // Not debug mode and the UnscaledCycleClock frequency is the CPU
+  // frequency.  Scale the CycleClock to prevent overflow if someone
+  // tries to represent the time as cycles since the Unix epoch.
+  static constexpr int32_t kShift = 1;
+#else
+  // Not debug mode and the UnscaledCycleClock isn't operating at the
+  // raw CPU frequency. There is no need to do any scaling, so don't
+  // needlessly sacrifice precision.
+  static constexpr int32_t kShift = 0;
+#endif
+#else   // NDEBUG
+  // In debug mode use a different shift to discourage depending on a
+  // particular shift value.
+  static constexpr int32_t kShift = 2;
+#endif  // NDEBUG
+
+  static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
+  ABSL_CONST_INIT static std::atomic<CycleClockSourceFunc> cycle_clock_source_;
+#endif  //  ABSL_USE_UNSCALED_CYCLECLOC
+
   CycleClock() = delete;  // no instances
   CycleClock(const CycleClock&) = delete;
   CycleClock& operator=(const CycleClock&) = delete;
-};
 
-using CycleClockSourceFunc = int64_t (*)();
+  friend class CycleClockSource;
+};
 
 class CycleClockSource {
  private:
@@ -87,6 +117,41 @@ class CycleClockSource {
   static void Register(CycleClockSourceFunc source);
 };
 
+#if ABSL_USE_UNSCALED_CYCLECLOCK
+
+inline CycleClockSourceFunc CycleClock::LoadCycleClockSource() {
+#if !defined(__x86_64__)
+  // Optimize for the common case (no callback) by first doing a relaxed load;
+  // this is significantly faster on non-x86 platforms.
+  if (cycle_clock_source_.load(std::memory_order_relaxed) == nullptr) {
+    return nullptr;
+  }
+#endif  // !defined(__x86_64__)
+
+  // This corresponds to the store(std::memory_order_release) in
+  // CycleClockSource::Register, and makes sure that any updates made prior to
+  // registering the callback are visible to this thread before the callback
+  // is invoked.
+  return cycle_clock_source_.load(std::memory_order_acquire);
+}
+
+// Accessing globals in inlined code in Window DLLs is problematic.
+#ifndef _WIN32
+inline int64_t CycleClock::Now() {
+  auto fn = LoadCycleClockSource();
+  if (fn == nullptr) {
+    return base_internal::UnscaledCycleClock::Now() >> kShift;
+  }
+  return fn() >> kShift;
+}
+#endif
+
+inline double CycleClock::Frequency() {
+  return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
+}
+
+#endif  // ABSL_USE_UNSCALED_CYCLECLOCK
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
diff --git a/absl/base/internal/unscaledcycleclock.cc b/absl/base/internal/unscaledcycleclock.cc
index 4d352bd1..7b79d19e 100644
--- a/absl/base/internal/unscaledcycleclock.cc
+++ b/absl/base/internal/unscaledcycleclock.cc
@@ -49,12 +49,6 @@ double UnscaledCycleClock::Frequency() {
 
 #elif defined(__x86_64__)
 
-int64_t UnscaledCycleClock::Now() {
-  uint64_t low, high;
-  __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
-  return (high << 32) | low;
-}
-
 double UnscaledCycleClock::Frequency() {
   return base_internal::NominalCPUFrequency();
 }
diff --git a/absl/base/internal/unscaledcycleclock.h b/absl/base/internal/unscaledcycleclock.h
index 681ff8f9..07f867a6 100644
--- a/absl/base/internal/unscaledcycleclock.h
+++ b/absl/base/internal/unscaledcycleclock.h
@@ -115,6 +115,16 @@ class UnscaledCycleClock {
   friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency;
 };
 
+#if defined(__x86_64__)
+
+inline int64_t UnscaledCycleClock::Now() {
+  uint64_t low, high;
+  __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
+  return (high << 32) | low;
+}
+
+#endif
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl