Use faster clock_gettime() instead of sysctl() to get current ticks on iOS10

base/time/time_mac.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/time/time.h"
 
 #include <CoreFoundation/CFDate.h>
 #include <CoreFoundation/CFTimeZone.h>
 #include <mach/mach.h>
 #include <mach/mach_time.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/sysctl.h>
 #include <sys/time.h>
 #include <sys/types.h>
 #include <time.h>
 
 #include "base/logging.h"
 #include "base/mac/mach_logging.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/scoped_mach_port.h"
 #include "base/macros.h"
 #include "base/numerics/safe_conversions.h"
 #include "build/build_config.h"
 
+#if defined(OS_IOS)
+#include <time.h>
+#include "base/ios/ios_util.h"
+#endif
+
 namespace {
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
 int64_t MachAbsoluteTimeToTicks(uint64_t mach_absolute_time) {
   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);
     MACH_DCHECK(kr == KERN_SUCCESS, kr) << "mach_timebase_info";
   }
 
   // timebase_info converts absolute time tick units into nanoseconds.  Convert
   // to microseconds up front to stave off overflows.
   base::CheckedNumeric<uint64_t> result(mach_absolute_time /
                                         base::Time::kNanosecondsPerMicrosecond);
   result *= timebase_info.numer;
   result /= timebase_info.denom;
 
   // Don't bother with the rollover handling that the Windows version does.
   // With numer and denom = 1 (the expected case), the 64-bit absolute time
   // reported in nanoseconds is enough to last nearly 585 years.
   return base::checked_cast<int64_t>(result.ValueOrDie());
 }
 #endif  // defined(OS_MACOSX) && !defined(OS_IOS)
 
+// Returns monotonically growing number of ticks in microseconds since some
+// unspecified starting point.
 int64_t ComputeCurrentTicks() {
 #if defined(OS_IOS)
+  // iOS 10 supports clock_gettime(CLOCK_MONOTONIC, ...), which is
+  // around 15 times faster than sysctl() call. Use it if possible;
+  // otherwise, fall back to sysctl().
+  if (base::ios::IsRunningOnIOS10OrLater()) {
+    struct timespec tp;
+    if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0) {
+      return tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
+    }
+  }
+
   // 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, arraysize(mib), &boottime, &size, nullptr, 0);
   DCHECK_EQ(KERN_SUCCESS, kr);
   base::TimeDelta time_difference =
@@ skipping 207 matching lines @@
   return Clock::MAC_MACH_ABSOLUTE_TIME;
 #endif  // defined(OS_IOS)
 }
 
 // static
 ThreadTicks ThreadTicks::Now() {
   return ThreadTicks(ComputeThreadTicks());
 }
 
 }  // namespace base