Bug 1429764 details a test failure that was asserting that the performance navigation
timers were strictly increasing (or equal). fetchStart should have a timestamp before
domainLookupStart. But it didn't.
The problem is two-fold. This corrects the test and the issue by addressing one part
of the problem, the second part of the problem needs to be written up in a new bug
and addressed there. (That bug is not yet filed at writing, but see dependencies of
1429764 in the future to find it.)
The second, and underlying, problem is that calling ReduceTimerPrecision with the
same value multiple times may continually reduce it. Meaning that the first you call
it with, say, .75, (and a precision of .20), it will be reduced to .6. The second time
you call it (with .6), instead of staying at .6 it will be reduced to .4. This is
because floats are fuzzy. Inside ReduceTimerPrecision we are multiplying a decimal by
a decimal, so while floor(.6 / .20) should equal 3, sometimes it's actually 2.999...
which gets floors to 2, gets multiplied again by .2, and which results in .4
If that's the underlying problem, the first, and surface, problem is - why are we
calling ReduceTimerPrecision multiple times? We shouldn't be. That's what this
patch fixes.
TimeStampToDOMHighResOrFetchStart will return either TimeStampToDOMHighRes() or
FetchStartHighRes(). FetchStartHighRes() internally calls TimeStampToDOMHighRes
and then ReduceTimerPrecision - this is where (some of) the two reduction calls
happen - because TimeStampToDOMHighRes itself calls ReduceTimerPrecision also.
I remove the ReduceTimerPrecision from TimeStampToDOMHighRes. FetchStartHighRes
will now only call ReduceTimerPrecision once, at the end of the return.
But we have to fix places we call TimeStampToDOMHighResOrFetchStart, because the
callers of that function also call ReduceTimerPrecision. So if
TimeStampToDOMHighResOrFetchStart returned FetchStartHighRes, we'd be calling
ReduceTimerPrecision twice for those callers.
So inside first off, we remove the outer call to ReduceTimerPrecision. that
surrounds the 5 or so callsites of TimeStampToDOMHighResOrFetchStart. Then
inside of TimeStampToDOMHighResOrFetchStart we return either FetchStartHighRes
(which is has already called ReduceTimerPrecision) or we call
ReduceTimerPrecision with the value.
Now. TimeStampToDOMHighRes was used in more places than just FetchStartHighRes -
there were several other places where we were doing double rounding, and this
fixed those as well. AsyncOpenHighRes, WorkerStartHighRes, DomainLookupEndHighRes,
ConnectStartHighRes, SecureConnectionStartHighRes, ConnectEndHighRes, and
ResponseEndHighRes.
MozReview-Commit-ID: K5nHql135rb
Implements PerformanceTiming, nsITimedChannel, and devtools 'tls setup'
Also captures telemetry on this as we do for all other attributes of timedChannel
Also propogates some null transaction timings onto first real
transaction of a connection
MozReview-Commit-ID: 47TQJYVHnKC
This patch is going to neutralize the threat of fingerprinting of performance API
by spoofing the value of performance timing into 0, making getEntries* functions
always returns an empty list and making mark() and measure() into NOP methods.
In addition, this patch changes nsContentUtils::ShouldResistFingerprinting() to
allow it can be called in both main thread and worker threads.
MozReview-Commit-ID: C8Jt7KEMe5e
