Refactor monotonic clock interface and use raw tick values in stopwatch

runtime/bin/utils_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 "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include <errno.h>  // NOLINT
 #include <netdb.h>  // NOLINT
 #include <mach/mach.h>  // NOLINT
@@ skipping 56 matching lines @@
 char* StringUtils::Utf8ToConsoleString(
     char* utf8, intptr_t len, intptr_t* result_len) {
   UNIMPLEMENTED();
   return NULL;
 }
 
 bool ShellUtils::GetUtf8Argv(int argc, char** argv) {
   return false;
 }
 
+static mach_timebase_info_data_t timebase_info;
+
 void TimerUtils::InitOnce() {
+  kern_return_t kr = mach_timebase_info(&timebase_info);
+  ASSERT(KERN_SUCCESS == kr);
 }
 
 int64_t TimerUtils::GetCurrentMonotonicMillis() {
   return GetCurrentMonotonicMicros() / 1000;
 }
 
 int64_t TimerUtils::GetCurrentMonotonicMicros() {
 #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);
-  }
-
+  ASSERT(timebase_info.denom != 0);
   // timebase_info converts absolute time tick units into nanoseconds.  Convert
   // to microseconds.
   int64_t result = mach_absolute_time() / kNanosecondsPerMicrosecond;
   result *= timebase_info.numer;
   result /= timebase_info.denom;
   return result;
 #endif  // TARGET_OS_IOS
 }
 
 void TimerUtils::Sleep(int64_t millis) {
@@ skipping 14 matching lines @@
     ASSERT(errno == EINTR);
     // Copy remainder into requested and repeat.
     req = rem;
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)