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Concurrent pantsd: Swap uncacheability for run-scoped results - #23616
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tobni
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category:internal
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| fn has_uncacheable_deps(&self) -> bool { | ||
| /// The Run which may consume this result, if it is confined to one. | ||
| fn uncacheable_run_id(&self) -> Option<RunId> { |
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uncacheable_run_id doesn't stand out to me as a very descriptive name. Maybe include some concept of the fact that it is the run ID for another consumer (going by the comment "may consume this result")?
Also, overall, what happens if there is more than one consumer of the result? (I'm reacting to the comment saying "if it is confined to one."
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Renamed to run_scope. It's the Run that produced the result, not another consumer's. All of consumers within that Run share the result, but other runs will treat it as dirty, always.
| let (entered_tx, entered_rx) = watch::channel(false); | ||
| let (release_tx, release_rx) = watch::channel(false); |
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Why a Tokio watch instead of a one-shot channel? Watches would generally be used for passing around values like configuration data and are multi-producer, multi-consumer. Am I missing something?
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I was trying to avoid a mutex, which I now realize was not worth it. Switched!
A Run which attaches to another Run's in-flight attempt cannot consume its run-scoped result, so it re-enters to compute its own.
Names the result, generation and run_scope fields.
complete() sets the generation and run scope itself.
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NodeResult holds the producing RunId in place of an "uncacheable" bool. A Run that attaches to an in-flight attempt started by another Run re-enters get_node_result instead of taking that attempt's result.
Nothing can observe another Run's attempt under the pantsd concurrency lock, so this change is behaviour-preserving work.
See https://docs.google.com/document/d/1XEO55efGI8x91wGiVjmlFpUORJeQpZ2xF4zQoSE4TuY/edit?tab=t.0#heading=h.apz3211m77eg for design intent.