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Change "global monotonic clock" to "shared" and expose new algorithm "unsafe shared current time" #107

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merged 6 commits into from
Mar 4, 2021
Merged

Change "global monotonic clock" to "shared" and expose new algorithm "unsafe shared current time" #107

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8ab4d69
Change "global monotonic clock" to "universal"
noamr Mar 3, 2021
4467c38
Unexport universal monotonic clock
noamr Mar 3, 2021
eacb67e
Rename universal to shared to avoid amgibuity with UTC
noamr Mar 3, 2021
9a32be5
Fix nit
noamr Mar 4, 2021
af53ce4
Fix nit
noamr Mar 4, 2021
4b53a3b
CR nits
noamr Mar 4, 2021
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27 changes: 14 additions & 13 deletions index.html
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Original file line number Diff line number Diff line change
Expand Up @@ -259,17 +259,17 @@ <h3>Time Origin</h3>
<li>Assert that <var>global</var>'s <a>time origin</a> is not undefined.
</li>
<li>Let <var>t1</var> be the {{DOMHighResTimeStamp}} representing the
high resolution time at which the <a>global monotonic clock</a> is zero.
high resolution time at which the <a>shared monotonic clock</a> is zero.
</li>
<li>Let <var>t2</var> be the {{DOMHighResTimeStamp}} representing the
high resolution time value of the <a>global monotonic clock</a> at <var>
high resolution time value of the <a>shared monotonic clock</a> at <var>
global</var>'s <a>time origin</a>.
</li>
<li>Return the sum of <var>t1</var> and <var>t2</var>.</li>
</ul>
<p class="note">The <a>time origin timestamp</a> and the value returned by
<a>Date.now()</a> executed at "zero time" can differ because the former is
recorded with respect to a global monotonic clock that is not subject to
recorded with respect to a shared monotonic clock that is not subject to
system and user clock adjustments, clock skew, and so on—see <a href=
"#sec-monotonic-clock"></a>.</p>
<p>
Expand All @@ -286,7 +286,7 @@ <h3>Time Origin</h3>
<p>The <dfn data-export="">current high resolution time</dfn> given a
[=/global object=] |current global| must run the following steps:
<ul>
<li>Let |current time| be the present time.</li>
<li>Let |unsafe shared current time| be the |shared current time|.</li>
<li>Let |settings object| be |current global|'s [=relevant settings object=].</li>
<li>Let |time resolution| be 100 microseconds, or a higher
<a>implementation-defined</a> value.</li>
Expand All @@ -300,11 +300,13 @@ <h3>Time Origin</h3>
<li>Return the result of [=relative high resolution time=] given
|current time| and |current global|.</li>
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</ul>
<p>The <dfn data-export="">unsafe shared current time</dfn> must return the
current value of the |shared monotonic clock|.
</section>
<section id="sec-domhighrestimestamp">
<h3>The <dfn data-export="">DOMHighResTimeStamp</dfn> typedef</h3>
<p>The {{DOMHighResTimeStamp}} type is used to store a time value in
milliseconds, measured relative from the <a>time origin</a>, <a>global
milliseconds, measured relative from the <a>time origin</a>, <a>shared
monotonic clock</a>, or a time value that represents a duration between two
{{DOMHighResTimeStamp}}s.</p>
<pre class='idl'>
Expand Down Expand Up @@ -370,17 +372,16 @@ <h3>Monotonic Clock</h3>
from the {{Performance.now()}} method MUST never be negative if the two
time values have the same <a>time origin</a>.</p>
<p data-link-for="Performance" data-tests='test_cross_frame_start.html'>The time values returned when
getting <code>performance.</code>{{timeOrigin}} MUST use the same <dfn data-export=
"">global monotonic clock</dfn> that is shared by <a>time origin</a>s, is
getting <code>performance.</code>{{timeOrigin}} MUST use the same <dfn>shared monotonic clock</dfn> that is shared by <a>time origin</a>s, is
monotonically increasing and not subject to system clock adjustments or
system clock skew, and whose reference point is the [[ECMA-262]]
<dfn data-no-export="" data-cite=
"ECMA-262#sec-time-values-and-time-range">time</dfn> definition - see
[[[#sec-privacy-security]]].</p>
<p class="note">The user agent can reset its global monotonic clock across
<p class="note">The user agent can reset its <a>shared monotonic clock</a> across
browser restarts, or whenever starting an isolated browsing session—e.g.
incognito or similar browsing mode. As a result, developers should not use
global timestamps as absolute time that holds its monotonic properties
shared timestamps as absolute time that holds its monotonic properties
across all past, present, and future contexts; in practice, the monotonic
properties only apply for contexts that can reach each other by exchanging
messages via one of the provided messaging mechanisms - e.g. `postMessage`,
Expand Down Expand Up @@ -456,22 +457,22 @@ <h3>Clock resolution</h3>
<h3>Clock drift</h3>
<p>This specification also defines an API that provides sub-millisecond
time resolution of the zero time of the time origin, which requires and
exposes a <a>global monotonic clock</a> to the application, and that must
be shared across all the browser contexts. The <a>global monotonic
exposes a <a>shared monotonic clock</a> to the application, and that must
be shared across all the browser contexts. The <a>shared monotonic
clock</a> does not need to be tied to physical time, but is recommended
to be set with respect to the [[ECMA-262]] definition of <a>time</a> to
avoid exposing new fingerprint entropy about the user — e.g. this time
can already be easily obtained by the application, whereas exposing a new
logical clock provides new information.</p>
<p>However, even with the above mechanism in place, the <a>global
<p>However, even with the above mechanism in place, the <a>shared
monotonic clock</a> may provide additional <a href=
"https://en.wikipedia.org/wiki/Clock_drift">clock drift</a> resolution.
Today, the application can timestamp the time-of-day and monotonic time
values (via <a>Date.now()</a> and {{Performance.now()}}) at multiple
points within the same context and observe drift between them—e.g. due to
automatic or user clock adjustments. With the {{Performance.timeOrigin}}
attribute, the attacker can also compare the time at which <a>time
origin</a> is zero, as reported by the <a>global monotonic clock</a>,
origin</a> is zero, as reported by the <a>shared monotonic clock</a>,
against the current time-of-day estimate of when it is zero (i.e. the
difference between `Date.now()-performance.now()` and
`performance.timeOrigin`) and potentially observe clock drift between
Expand Down