Refactor monotonic clock interface and use raw tick values in stopwatch

runtime/vm/os_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "vm/os.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 72 matching lines @@
   // gettimeofday has microsecond resolution.
   struct timeval tv;
   if (gettimeofday(&tv, NULL) < 0) {
     UNREACHABLE();
     return 0;
   }
   return (static_cast<int64_t>(tv.tv_sec) * 1000000) + tv.tv_usec;
 }
 
 
-int64_t OS::GetCurrentMonotonicMicros() {
+static mach_timebase_info_data_t timebase_info;
+
+
+int64_t OS::GetCurrentMonotonicTicks() {
 #if TARGET_OS_IOS
   // On iOS mach_absolute_time stops while the device is sleeping. Instead use
   // now - KERN_BOOTTIME to get a time difference that is not impacted by clock
   // changes. KERN_BOOTTIME will be updated by the system whenever the system
   // clock change.
   struct timeval boottime;
   int mib[2] = {CTL_KERN, KERN_BOOTTIME};
   size_t size = sizeof(boottime);
   int kr = sysctl(mib, sizeof(mib) / sizeof(mib[0]), &boottime, &size, NULL, 0);
   ASSERT(KERN_SUCCESS == kr);
   int64_t now = GetCurrentTimeMicros();
   int64_t origin = boottime.tv_sec * kMicrosecondsPerSecond;
   origin += boottime.tv_usec;
   return now - origin;
 #else
-  static mach_timebase_info_data_t timebase_info;
-  if (timebase_info.denom == 0) {
-    // Zero-initialization of statics guarantees that denom will be 0 before
-    // calling mach_timebase_info.  mach_timebase_info will never set denom to
-    // 0 as that would be invalid, so the zero-check can be used to determine
-    // whether mach_timebase_info has already been called.  This is
-    // recommended by Apple's QA1398.
-    kern_return_t kr = mach_timebase_info(&timebase_info);
-    ASSERT(KERN_SUCCESS == kr);
-  }
-
-  // timebase_info converts absolute time tick units into nanoseconds.  Convert
-  // to microseconds.
-  int64_t result = mach_absolute_time() / kNanosecondsPerMicrosecond;
+  ASSERT(timebase_info.denom != 0);
+  // timebase_info converts absolute time tick units into nanoseconds.
+  int64_t result = mach_absolute_time();
   result *= timebase_info.numer;
   result /= timebase_info.denom;
   return result;
 #endif  // TARGET_OS_IOS
 }
 
 
+int64_t OS::GetCurrentMonotonicFrequency() {
+#if TARGET_OS_IOS
+  return kMicrosecondsPerSecond;
+#else
+  return kNanosecondsPerSecond;
+#endif  // TARGET_OS_IOS
+}
+
+
+int64_t OS::GetCurrentMonotonicMicros() {
+#if TARGET_OS_IOS
+  ASSERT(GetCurrentMonotonicFrequency() == kMicrosecondsPerSecond);
+  return GetCurrentMonotonicTicks();
+#else
+  ASSERT(GetCurrentMonotonicFrequency() == kNanosecondsPerSecond);
+  return GetCurrentMonotonicTicks() / kNanosecondsPerMicrosecond;
+#endif  // TARGET_OS_IOS
+}
+
+
 void* OS::AlignedAllocate(intptr_t size, intptr_t alignment) {
   const int kMinimumAlignment = 16;
   ASSERT(Utils::IsPowerOfTwo(alignment));
   ASSERT(alignment >= kMinimumAlignment);
   // Temporary workaround until xcode is upgraded.
   // Mac guarantees malloc returns a 16 byte aligned memory chunk.
   // Currently we only allocate with 16-bye alignment.
   ASSERT(alignment == 16);
   // TODO(johnmccutchan): Remove hack and switch to posix_memalign.
   return malloc(size);
@@ skipping 214 matching lines @@
 }
 
 
 void OS::InitOnce() {
   // TODO(5411554): For now we check that initonce is called only once,
   // Once there is more formal mechanism to call InitOnce we can move
   // this check there.
   static bool init_once_called = false;
   ASSERT(init_once_called == false);
   init_once_called = true;
+  kern_return_t kr = mach_timebase_info(&timebase_info);
+  ASSERT(KERN_SUCCESS == kr);
 }
 
 
 void OS::Shutdown() {
 }
 
 
 void OS::Abort() {
   abort();
 }
 
 
 void OS::Exit(int code) {
   exit(code);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)