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script: Create a CrossProcessInstant to enable serializable monotonic time (#33282)

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Up until now, Servo was using a very old version of time to get a
cross-process monotonic timestamp (using `time::precise_time_ns()`).
This change replaces the usage of old time with a new serializable
monotonic time called `CrossProcessInstant` and uses it where `u64`
timestamps were stored before. The standard library doesn't provide this
functionality because it isn't something you can do reliably on all
platforms. The idea is that we do our best and then fall back
gracefully.

This is a big change, because Servo was using `u64` timestamps all over
the place some as raw values taken from `time::precise_time_ns()` and
some as relative offsets from the "navigation start," which is a concept
similar to DOM's `timeOrigin` (but not exactly the same). It's very
difficult to fix this situation without fixing it everywhere as the
`Instant` concept is supposed to be opaque. The good thing is that this
change clears up all ambiguity when passing times as a `time::Duration`
is unit agnostic and a `CrossProcessInstant` represents an absolute
moment in time.

The `time` version of `Duration` is used because it can both be negative
and is also serializable.

Good things:
 - No need too pass around `time` and `time_precise` any longer.
   `CrossProcessInstant` is also precise and monotonic.
 - The distinction between a time that is unset or at `0` (at some kind
   of timer epoch) is now gone.

There still a lot of work to do to clean up timing, but this is the
first step. In general, I've tried to preserve existing behavior, even
when not spec compliant, as much as possible. I plan to submit followup
PRs fixing some of the issues I've noticed.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This commit is contained in:
Martin Robinson 2024-09-05 11:50:09 -07:00 • committed by GitHub
parent 35baf056f6
commit 312cf0df08
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51 changed files with 854 additions and 665 deletions
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20
components/script/dom/servoparser/mod.rs
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@ -5,6 +5,7 @@
use std::borrow::Cow;
use std::cell::Cell;
use base::cross_process_instant::CrossProcessInstant;
use base::id::PipelineId;
use base64::engine::general_purpose;
use base64::Engine as _;
@ -937,11 +938,15 @@ impl FetchResponseListener for ParserContext {
parser.parse_sync();
}
//TODO only update if this is the current document resource
// TODO: Only update if this is the current document resource.
// TODO(mrobinson): Pass a proper fetch_start parameter here instead of `CrossProcessInstant::now()`.
if let Some(pushed_index) = self.pushed_entry_index {
let document = &parser.document;
let performance_entry =
PerformanceNavigationTiming::new(&document.global(), 0, 0, document);
let performance_entry = PerformanceNavigationTiming::new(
&document.global(),
CrossProcessInstant::now(),
document,
);
document
.global()
.performance()
@ -969,9 +974,12 @@ impl FetchResponseListener for ParserContext {
let document = &parser.document;
//TODO nav_start and nav_start_precise
let performance_entry =
PerformanceNavigationTiming::new(&document.global(), 0, 0, document);
// TODO: Pass a proper fetch start time here.
let performance_entry = PerformanceNavigationTiming::new(
&document.global(),
CrossProcessInstant::now(),
document,
);
self.pushed_entry_index = document
.global()
.performance()