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Bug 1004923 part 11 - Remove slow and bogus GetSystemTimeAdjustment call. r=njn

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This commit is contained in:
Jan de Mooij 2014-05-05 13:12:09 +02:00
parent a51cf37454
commit fd6099af33
1 changed files with 7 additions and 17 deletions
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24
js/src/prmjtime.cpp
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@ -206,22 +206,12 @@ PRMJ_Now()
cachedOffset = calibration.offset;
MUTEX_UNLOCK(&calibration.data_lock);
// Rather than assume the NT kernel ticks every 15.6ms, ask it.
double skewThreshold;
DWORD timeAdjustment, timeIncrement;
BOOL timeAdjustmentDisabled;
if (GetSystemTimeAdjustment(&timeAdjustment, &timeIncrement, &timeAdjustmentDisabled)) {
if (timeAdjustmentDisabled) {
// timeAdjustment is in units of 100ns.
skewThreshold = timeAdjustment / 10.0;
} else {
// timeIncrement is in units of 100ns.
skewThreshold = timeIncrement / 10.0;
}
} else {
// Default to 15.625 ms if the syscall fails.
skewThreshold = 15625.25;
}
// Assume the NT kernel ticks every 15.6 ms. Unfortunately there's no
// good way to determine this (NtQueryTimerResolution is an undocumented
// API), but 15.6 ms seems to be the max possible value. Hardcoding 15.6
// means we'll recalibrate if the highres and lowres timers diverge by
// more than 30 ms.
static const double KernelTickInMicroseconds = 15625.25;
// Check for clock skew.
double diff = lowresTime - highresTime;
@ -231,7 +221,7 @@ PRMJ_Now()
// itself, but I have only seen it triggered by another program
// doing some kind of file I/O. The symptoms are a negative diff
// followed by an equally large positive diff.
if (mozilla::Abs(diff) <= 2 * skewThreshold) {
if (mozilla::Abs(diff) <= 2 * KernelTickInMicroseconds) {
// No detectable clock skew.
return int64_t(highresTime);
}