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This allows accurate line numbers when reporting stylesheet errors.
@jdm This is going to require some effort to merge my changes with other recent changes to `ParserContext`. Because of that I would appreciate a quick sanity check before I put the time into performing the merge.
For example, should I store the `offset` as a u64, or should it be an Option?
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Source-Repo: https://github.com/servo/servo
Source-Revision: 94397ff0b4fed138241760770ff2d230985bed8a
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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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Source-Repo: https://github.com/servo/servo
Source-Revision: bb54f0a429de0e8b8861f8071b6cf82f73622664
