Several Tick counter improvements try #2."

This reverts commit c91d1738709b038fee84d569180cba2bbcbfe5d7.

BUG=

Review URL: https://codereview.webrtc.org/1452843003

Cr-Commit-Position: refs/heads/master@{#10682}
diff --git a/webrtc/modules/utility/source/process_thread_impl_unittest.cc b/webrtc/modules/utility/source/process_thread_impl_unittest.cc
index 34ed5c5..92cd561 100644
--- a/webrtc/modules/utility/source/process_thread_impl_unittest.cc
+++ b/webrtc/modules/utility/source/process_thread_impl_unittest.cc
@@ -251,8 +251,9 @@
   rtc::scoped_ptr<EventWrapper> called(EventWrapper::Create());
 
   MockModule module;
-  int64_t start_time = 0;
-  int64_t called_time = 0;
+  int64_t start_time;
+  int64_t called_time;
+
   // Ask for a callback after 1000ms.
   // TimeUntilNextProcess will be called twice.
   // The first time we use it to get the thread into a waiting state.
@@ -281,8 +282,6 @@
   EXPECT_CALL(module, ProcessThreadAttached(nullptr)).Times(1);
   thread.Stop();
 
-  ASSERT_GT(start_time, 0);
-  ASSERT_GT(called_time, 0);
   EXPECT_GE(called_time, start_time);
   uint32_t diff = called_time - start_time;
   // We should have been called back much quicker than 1sec.
diff --git a/webrtc/system_wrappers/include/tick_util.h b/webrtc/system_wrappers/include/tick_util.h
index f839ff6..6e3b05e 100644
--- a/webrtc/system_wrappers/include/tick_util.h
+++ b/webrtc/system_wrappers/include/tick_util.h
@@ -56,6 +56,8 @@
 
   static int64_t TicksToMilliseconds(const int64_t ticks);
 
+  static int64_t TicksToMicroseconds(const int64_t ticks);
+
   // Returns a TickTime that is ticks later than the passed TickTime.
   friend TickTime operator+(const TickTime lhs, const int64_t ticks);
   TickTime& operator+=(const int64_t& ticks);
@@ -112,6 +114,14 @@
   int64_t interval_;
 };
 
+inline int64_t TickInterval::Milliseconds() const {
+  return TickTime::TicksToMilliseconds(interval_);
+}
+
+inline int64_t TickInterval::Microseconds() const {
+  return TickTime::TicksToMicroseconds(interval_);
+}
+
 inline TickInterval operator+(const TickInterval& lhs,
                               const TickInterval& rhs) {
   return TickInterval(lhs.interval_ + rhs.interval_);
@@ -163,76 +173,10 @@
     return TickTime(QueryOsForTicks());
 }
 
-inline int64_t TickTime::MillisecondTimestamp() {
-  int64_t ticks = TickTime::Now().Ticks();
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (ticks * 1000) / qpfreq.QuadPart;
-#else
-  return ticks;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  return ticks / 1000000LL;
-#else
-  return ticks / 1000LL;
-#endif
-}
-
-inline int64_t TickTime::MicrosecondTimestamp() {
-  int64_t ticks = TickTime::Now().Ticks();
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (ticks * 1000) / (qpfreq.QuadPart / 1000);
-#else
-  return ticks * 1000LL;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  return ticks / 1000LL;
-#else
-  return ticks;
-#endif
-}
-
 inline int64_t TickTime::Ticks() const {
   return ticks_;
 }
 
-inline int64_t TickTime::MillisecondsToTicks(const int64_t ms) {
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (qpfreq.QuadPart * ms) / 1000;
-#else
-  return ms;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  return ms * 1000000LL;
-#else
-  return ms * 1000LL;
-#endif
-}
-
-inline int64_t TickTime::TicksToMilliseconds(const int64_t ticks) {
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (ticks * 1000) / qpfreq.QuadPart;
-#else
-  return ticks;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  return ticks / 1000000LL;
-#else
-  return ticks / 1000LL;
-#endif
-}
-
 inline TickTime& TickTime::operator+=(const int64_t& ticks) {
   ticks_ += ticks;
   return *this;
@@ -245,44 +189,6 @@
   : interval_(interval) {
 }
 
-inline int64_t TickInterval::Milliseconds() const {
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (interval_ * 1000) / qpfreq.QuadPart;
-#else
-  // interval_ is in ms
-  return interval_;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  // interval_ is in ns
-  return interval_ / 1000000;
-#else
-  // interval_ is usecs
-  return interval_ / 1000;
-#endif
-}
-
-inline int64_t TickInterval::Microseconds() const {
-#if _WIN32
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  LARGE_INTEGER qpfreq;
-  QueryPerformanceFrequency(&qpfreq);
-  return (interval_ * 1000000) / qpfreq.QuadPart;
-#else
-  // interval_ is in ms
-  return interval_ * 1000LL;
-#endif
-#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
-  // interval_ is in ns
-  return interval_ / 1000;
-#else
-  // interval_ is usecs
-  return interval_;
-#endif
-}
-
 inline TickInterval& TickInterval::operator+=(const TickInterval& rhs) {
   interval_ += rhs.interval_;
   return *this;
diff --git a/webrtc/system_wrappers/source/tick_util.cc b/webrtc/system_wrappers/source/tick_util.cc
index bc8fcfe..cae817d 100644
--- a/webrtc/system_wrappers/source/tick_util.cc
+++ b/webrtc/system_wrappers/source/tick_util.cc
@@ -17,6 +17,71 @@
 bool TickTime::use_fake_clock_ = false;
 int64_t TickTime::fake_ticks_ = 0;
 
+int64_t TickTime::MillisecondTimestamp() {
+  return TicksToMilliseconds(TickTime::Now().Ticks());
+}
+
+int64_t TickTime::MicrosecondTimestamp() {
+  return TicksToMicroseconds(TickTime::Now().Ticks());
+}
+
+int64_t TickTime::MillisecondsToTicks(const int64_t ms) {
+#if _WIN32
+  return ms;
+#elif defined(WEBRTC_LINUX)
+  return ms * 1000000LL;
+#elif defined(WEBRTC_MAC)
+  // TODO(pbos): Fix unsafe use of static locals.
+  static double timebase_from_millisecond_fract = 0.0;
+  if (timebase_from_millisecond_fract == 0.0) {
+    mach_timebase_info_data_t timebase;
+    (void)mach_timebase_info(&timebase);
+    timebase_from_millisecond_fract = (timebase.denom * 1e6) / timebase.numer;
+  }
+  return ms * timebase_from_millisecond_fract;
+#else
+  return ms * 1000LL;
+#endif
+}
+
+int64_t TickTime::TicksToMilliseconds(const int64_t ticks) {
+#if _WIN32
+  return ticks;
+#elif defined(WEBRTC_LINUX)
+  return ticks / 1000000LL;
+#elif defined(WEBRTC_MAC)
+  // TODO(pbos): Fix unsafe use of static locals.
+  static double timebase_microsecond_fract = 0.0;
+  if (timebase_microsecond_fract == 0.0) {
+    mach_timebase_info_data_t timebase;
+    (void)mach_timebase_info(&timebase);
+    timebase_microsecond_fract = timebase.numer / (timebase.denom * 1e6);
+  }
+  return ticks * timebase_microsecond_fract;
+#else
+  return ticks;
+#endif
+}
+
+int64_t TickTime::TicksToMicroseconds(const int64_t ticks) {
+#if _WIN32
+  return ticks * 1000LL;
+#elif defined(WEBRTC_LINUX)
+  return ticks / 1000LL;
+#elif defined(WEBRTC_MAC)
+  // TODO(pbos): Fix unsafe use of static locals.
+  static double timebase_microsecond_fract = 0.0;
+  if (timebase_microsecond_fract == 0.0) {
+    mach_timebase_info_data_t timebase;
+    (void)mach_timebase_info(&timebase);
+    timebase_microsecond_fract = timebase.numer / (timebase.denom * 1e3);
+  }
+  return ticks * timebase_microsecond_fract;
+#else
+  return ticks;
+#endif
+}
+
 void TickTime::UseFakeClock(int64_t start_millisecond) {
   use_fake_clock_ = true;
   fake_ticks_ = MillisecondsToTicks(start_millisecond);
@@ -27,20 +92,14 @@
   fake_ticks_ += MillisecondsToTicks(milliseconds);
 }
 
+// Gets the native system tick count. The actual unit, resolution, and epoch
+// varies by platform:
+// Windows: Milliseconds of uptime with rollover count in the upper 32-bits.
+// Linux/Android: Nanoseconds since the Unix epoch.
+// Mach (Mac/iOS): "absolute" time since first call.
+// Unknown POSIX: Microseconds since the Unix epoch.
 int64_t TickTime::QueryOsForTicks() {
-  TickTime result;
 #if _WIN32
-  // TODO(wu): Remove QueryPerformanceCounter implementation.
-#ifdef USE_QUERY_PERFORMANCE_COUNTER
-  // QueryPerformanceCounter returns the value from the TSC which is
-  // incremented at the CPU frequency. The algorithm used requires
-  // the CPU frequency to be constant. Technology like speed stepping
-  // which has variable CPU frequency will therefore yield unpredictable,
-  // incorrect time estimations.
-  LARGE_INTEGER qpcnt;
-  QueryPerformanceCounter(&qpcnt);
-  result.ticks_ = qpcnt.QuadPart;
-#else
   static volatile LONG last_time_get_time = 0;
   static volatile int64_t num_wrap_time_get_time = 0;
   volatile LONG* last_time_get_time_ptr = &last_time_get_time;
@@ -53,11 +112,11 @@
     // 0x0fffffff ~3.1 days, the code will not take that long to execute
     // so it must have been a wrap around.
     if (old > 0xf0000000 && now < 0x0fffffff) {
+      // TODO(pbos): Fix unsafe use of static locals.
       num_wrap_time_get_time++;
     }
   }
-  result.ticks_ = now + (num_wrap_time_get_time << 32);
-#endif
+  return now + (num_wrap_time_get_time << 32);
 #elif defined(WEBRTC_LINUX)
   struct timespec ts;
   // TODO(wu): Remove CLOCK_REALTIME implementation.
@@ -66,33 +125,24 @@
 #else
   clock_gettime(CLOCK_MONOTONIC, &ts);
 #endif
-  result.ticks_ = 1000000000LL * static_cast<int64_t>(ts.tv_sec) +
-      static_cast<int64_t>(ts.tv_nsec);
+  return 1000000000LL * ts.tv_sec + ts.tv_nsec;
 #elif defined(WEBRTC_MAC)
-  static mach_timebase_info_data_t timebase;
-  if (timebase.denom == 0) {
-    // Get the timebase if this is the first time we run.
-    // Recommended by Apple's QA1398.
-    kern_return_t retval = mach_timebase_info(&timebase);
-    if (retval != KERN_SUCCESS) {
-      // TODO(wu): Implement RTC_CHECK for all the platforms. Then replace this
-      // with a RTC_CHECK_EQ(retval, KERN_SUCCESS);
-#ifndef WEBRTC_IOS
-      asm("int3");
-#else
-      __builtin_trap();
-#endif  // WEBRTC_IOS
-    }
+  // Return absolute time as an offset from the first call to this function, so
+  // that we can do floating-point (double) operations on it without losing
+  // precision. This holds true until the elapsed time is ~11 days,
+  // at which point we'll start to lose some precision, though not enough to
+  // matter for millisecond accuracy for another couple years after that.
+  // TODO(pbos): Fix unsafe use of static locals.
+  static uint64_t timebase_start = 0;
+  if (timebase_start == 0) {
+    timebase_start = mach_absolute_time();
   }
-  // Use timebase to convert absolute time tick units into nanoseconds.
-  result.ticks_ = mach_absolute_time() * timebase.numer / timebase.denom;
+  return mach_absolute_time() - timebase_start;
 #else
   struct timeval tv;
   gettimeofday(&tv, NULL);
-  result.ticks_ = 1000000LL * static_cast<int64_t>(tv.tv_sec) +
-      static_cast<int64_t>(tv.tv_usec);
+  return 1000000LL * tv.tv_sec + tv.tv_usec;
 #endif
-  return result.ticks_;
 }
 
 }  // namespace webrtc