On Wed, Apr 8, 2020 at 6:35 PM Tom Ritter <t...@mozilla.com> wrote:
> I'm pretty sure that if you're not in the System Principal; your
> timestamps from the performance object are going to be clamped to 1ms
> resolution (and potentially jittered forward....)
>
ChromeUtils is only available to System Principal code.
>
> I'm not sure in what context this will be used; or if there's
> something that would prevent this timing behavior from taking effect;
> but it would be worth confirming and documenting I think.
>
> -tom
>
> On Tue, Apr 7, 2020 at 8:22 AM Florian Quèze <flor...@queze.net> wrote:
> >
> > I recently landed a new scriptable API to add profiler markers:
> ChromeUtils.addProfilerMarker.
> > This makes it possible for chrome privileged JS code to insert profiler
> markers that (optionally) have a duration and an associated text.
> >
> > Examples:
> >
> > Adding a marker without duration:
> > ChromeUtils.addProfilerMarker("markerName");
> > Adding a marker showing the time it took to do something:
> > let startTime = performance.now();
> > /* do stuff */
> > ChromeUtils.addProfilerMarker("markerName", startTime);
> > The performance object is available in windows and workers. In JS
> modules, use Cu.now() instead of performance.now().
> > Adding a marker with a duration and an associated extra string:
> > ChromeUtils.addProfilerMarker("markerName", startTime, "marker text");
> >
> >
> > Hopefully, this should make it easier to show clearly in the profiler
> what our JS code is doing. The first use I made of this was to show the
> OS.File operations that are done asynchronously (example profile:
> https://perfht.ml/2RhAKXF).
> >
> > Scriptable marker APIs that already existed:
> >
> > Adding a marker from XPCOM-enabled contexts:
> > if (Services.profiler) {
> > Services.profiler.addMarker("markerName");
> > }
> > The null check was required to avoid exceptions on tier3 platforms that
> don't implement the profiler service.
> > We will probably want to deprecate this API and migrate all existing
> callers.
> > Adding a 'UserTiming' marker with a duration in a window or worker:
> > performance.mark("markName");
> > /* do stuff */
> > performance.measure("marker text", "markName");
> > This will add a marker named UserTiming with the "marker text"
> associated text, and the duration between the performance.mark and the
> performance.measure calls. However, the performance.measure implementation
> is slow enough that it adds significant overhead if called frequently.
> > This API will remain available, but should be avoided for chrome
> privileged code.
> >
> >
> > --
> > Florian Quèze
> > _______________________________________________
> > firefox-dev mailing list
> > firefox-...@mozilla.org
> > https://mail.mozilla.org/listinfo/firefox-dev
> _______________________________________________
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>
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