feat: allow an external semaphore for executor task concurrency#1892
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milenkovicm merged 5 commits intoJul 20, 2026
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Adds an optional available_task_slots: Option<Arc<Semaphore>> parameter to the executor poll_loop. When provided, the caller supplies the semaphore that bounds concurrent task execution; this enables sharing it across poll loops connected to different schedulers and observing executor busy state via available_permits(). When None, the loop creates one internally sized to the executor's task slots (unchanged behavior). Ported from #14 for upstreaming. Note: layers on the poll_loop signature; if landed after #12 (poll_now_notify) it needs a trivial rebase to add both parameters.
andygrove
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Jun 26, 2026
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Thanks for upstreaming this. The opt-in shape is clean and the default behavior is preserved exactly, which makes it easy to reason about. My only notes are a couple of doc-comment clarifications for the shared-semaphore path. Separately, would it be worth a small test that passes in a semaphore and asserts the loop uses it rather than creating its own? I realize that's awkward to set up against poll_loop, so feel free to wave it off if it's more trouble than it's worth.
This review was prepared with the help of an LLM.
andygrove
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Jun 26, 2026
martin-g
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Jun 29, 2026
- Handle AcquireError from semaphore acquire/acquire_owned by mapping to BallistaError instead of panicking, since the semaphore may now be externally owned and closed by the caller - Assert that the provided semaphore has at least one permit on entry to fail fast rather than deadlock - Rewrite poll_loop doc comment to be public-facing: remove references to internal variable names and implementation types, document shared- semaphore over-commit semantics and sizing tradeoffs in behavioral terms, and add a # Panics section for the zero-permit case
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thanks @Jeadie, looks like one clippy issue left |
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@milenkovicm this should be good now |
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thanks @Jeadie @phillipleblanc & @andygrove |
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Which issue does this PR close?
None
Closes #.Suggested by @milenkovicm that we should upstream our changes (see comment).Rationale for this change
Useful in spiceai/datafusion-ballista for production features.
What changes are included in this PR?
Adds an optional
available_task_slots: Option<Arc<Semaphore>>parameter to the executorpoll_loop. When provided, the caller supplies the semaphore that bounds concurrent task execution; whenNone, the loop creates one internally sized to the executor's task slots (unchanged behavior).Enables:
available_permits().Ported from spiceai#14.