Reviewed by @emilio in [bug 1329088](https://bugzilla.mozilla.org/show_bug.cgi?id=1329088).
r? @emilio
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
Source-Repo: https://github.com/servo/servo
Source-Revision: 5c56640508b4f24a67fe92c5d3179d89d030e959
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Reviewed by @emilio in [bug 1353191](https://bugzilla.mozilla.org/show_bug.cgi?id=1353191).
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
Source-Repo: https://github.com/servo/servo
Source-Revision: 5f6c27bb945eba1242be2fb4812ea5095ef26377
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Before this PR, every object reflected in CSSOM is in `Arc<RwLock<_>>` to enable safe (synchronized) mutable aliasing. Acquiring all these locks has significant cost during selector matching:
* https://bugzilla.mozilla.org/show_bug.cgi?id=1311469
* https://bugzilla.mozilla.org/show_bug.cgi?id=1335941
* https://bugzilla.mozilla.org/show_bug.cgi?id=1339703
This PR introduce a mechanism to protect many objects with the same `RwLock` that only needs to be acquired once.
In Stylo, there is one such lock per process (in a `lazy_static`), used for everything.
I non-Stylo Servo, I originally intended to have one such lock per document (for author-origin stylesheets, and one per process for user-agent and user sytlesheets since they’re shared across documents, and never mutated anyway). However I failed to have the same document-specific (or pipeline-specific) `Arc` reachable from both `Document` nodes and `LayoutThread`. Recursively following callers lead me to include this `Arc` in `UnprivilegedPipelineContent`, but that needs to be serializable. So there is a second process-wide lock.
This was previously #15998, closed accidentally.
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- [ ] These changes fix #__ (github issue number if applicable).
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Source-Repo: https://github.com/servo/servo
Source-Revision: bb54f0a429de0e8b8861f8071b6cf82f73622664
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extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
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This is on top of https://github.com/servo/servo/pull/15928.
Now that cascade() gets a Device ref, we can use the default computed values
from there to avoid propagating that state all over the place.
Source-Repo: https://github.com/servo/servo
Source-Revision: 8c8edb8731dc01d254839d0922590fba72f278c6
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extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
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