Reimplement AtomicRefCell with pure atomics
While reviewing @bzbarsky's patches in [1], I started typing out some lore about how mutable AtomicRefCell borrows are actually cheaper than immutable ones, so we should prefer them where possible. But then I decided that this was a really dumb state of affairs and that we should just fix AtomicRefCell instead, and implement a proper AtomicRef{,Mut}::map while we were at it. So here we are.
This PR adds a from-scratch implementation of AtomicRefCell that aims to be 100% sound, even in unrealistic overflow scenarios. We should probably get this on crates.io eventually, but I want to land it landed in-tree first.
With this implementation, each operation (borrow or release) is one atomic instruction, and all borrow/release pairs (mutable or immutable) take 12 ns on my machine, which is what I'd expect. This is a 50% improvement over the previous implementation in the immutable case.
There may be some places where we could get away with Ordering::Release instead of Ordering::AcqRel, but it didn't seem worth it to try to reason it out.
r? @Manishearth
CC @emilio @SimonSapin @heycam @upsuper
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1298588
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Allow passing --nocapture argument to test-unit mach command
This adds the ` --nocapture` argument to the test-unit mach command.
Defaulting to false, when given it passes `-- --nocapture` to cargo test to show stdout during test-unit runs.
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Fix browserhtml path
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I'd missed something in #14817, which now prevents us from running `./mach run -r -b`. @UK992 pointed this in the PR, but it got merged soon 😐
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Updating http_network_or_cache_fetch to better match the fetch API spec
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Remove useless call to map() in constellation.rs
Remove a little bit useless call to map() in constellation.rs :)
Context: https://github.com/servo/servo/pull/14724/files#r94317893
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Remove duplicate code in mach
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Move get_browserhtml_path to command_base
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