static PRUint64
ClockResolutionNs()
{
// NB: why not rely on clock_getres()? Two reasons: (i) it might
// lie, and (ii) it might return an "ideal" resolution that while
// theoretically true, could never be measured in practice. Since
// clock_gettime() likely involves a system call on your platform,
// the "actual" timing resolution shouldn't be lower than syscall
// overhead.
PRUint64 start = ClockTimeNs();
PRUint64 end = ClockTimeNs();
PRUint64 minres = (end - start);
// 10 total trials is arbitrary: what we're trying to avoid by
// looping is getting unlucky and being interrupted by a context
// switch or signal, or being bitten by paging/cache effects
for (int i = 0; i < 9; ++i) {
start = ClockTimeNs();
end = ClockTimeNs();
PRUint64 candidate = (start - end);
if (candidate < minres)
minres = candidate;
}
if (0 == minres) {
// measurable resolution is either incredibly low, ~1ns, or very
// high. fall back on clock_getres()
struct timespec ts;
if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
minres = TimespecToNs(ts);
}
}
if (0 == minres) {
// clock_getres probably failed. fall back on NSPR's resolution
// assumption
minres = 1 * kNsPerMs;
}
return minres;
}
TimeStamp
TimeStamp::Now(bool aHighResolution)
{
return TimeStamp(ClockTimeNs());
}
TimeStamp
TimeStamp::Now()
{
return TimeStamp(ClockTimeNs());
}
void
TimeStamp::RecordProcessRestart()
{
PR_SetEnv(PR_smprintf("MOZ_APP_RESTART=%lld", ClockTimeNs()));
sProcessCreation = TimeStamp();
}
