class HighResNowSingleton {
public:
HighResNowSingleton()
- : ticks_per_second_(0),
- skew_(0) {
- InitializeClock();
+ : ticks_per_second_(0),
+ skew_(0) {
base::CPU cpu;
if (IsBuggyAthlon(cpu))
- DisableHighResClock();
- }
+ return;
- bool IsUsingHighResClock() {
- return ticks_per_second_ != 0.0;
+ // Synchronize the QPC clock with GetSystemTimeAsFileTime.
+ LARGE_INTEGER ticks_per_sec = {0};
+ if (!QueryPerformanceFrequency(&ticks_per_sec))
+ return; // QPC is not available.
+ ticks_per_second_ = ticks_per_sec.QuadPart;
+
+ skew_ = UnreliableNow() - ReliableNow();
}
- void DisableHighResClock() {
- ticks_per_second_ = 0.0;
+ bool IsUsingHighResClock() {
+ return ticks_per_second_ != 0;
}
TimeDelta Now() {
}
private:
- // Synchronize the QPC clock with GetSystemTimeAsFileTime.
- void InitializeClock() {
- LARGE_INTEGER ticks_per_sec = {0};
- if (!QueryPerformanceFrequency(&ticks_per_sec))
- return; // Broken, we don't guarantee this function works.
- ticks_per_second_ = ticks_per_sec.QuadPart;
-
- skew_ = UnreliableNow() - ReliableNow();
- }
-
// Get the number of microseconds since boot in an unreliable fashion.
int64 UnreliableNow() {
LARGE_INTEGER now;
}
typedef TimeDelta (*NowFunction)(void);
-NowFunction now_function = RolloverProtectedNow;
bool CPUReliablySupportsHighResTime() {
base::CPU cpu;
return true;
}
+TimeDelta InitialNowFunction();
+
+volatile NowFunction now_function = InitialNowFunction;
+
+TimeDelta InitialNowFunction() {
+ if (!CPUReliablySupportsHighResTime()) {
+ InterlockedExchangePointer(
+ reinterpret_cast<void* volatile*>(&now_function),
+ &RolloverProtectedNow);
+ return RolloverProtectedNow();
+ }
+ InterlockedExchangePointer(
+ reinterpret_cast<void* volatile*>(&now_function),
+ &HighResNowWrapper);
+ return HighResNowWrapper();
+}
+
} // namespace
// static
}
// static
-bool TimeTicks::SetNowIsHighResNowIfSupported() {
- if (!CPUReliablySupportsHighResTime()) {
- return false;
- }
-
- now_function = HighResNowWrapper;
- return true;
-}
-
-// static
TimeTicks TimeTicks::Now() {
return TimeTicks() + now_function();
}