par-map: chunking strategy and cancellation (ILO-354)#670
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needs manual rebase (conflicts in: src/builtins.rs) |
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needs manual — rebase conflict in non-doc file(s) |
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needs manual rebase — touches src/builtins.rs, src/interpreter/mod.rs, src/vm/mod.rs |
Implements `par-map fn xs [n]` — a general concurrency primitive that applies a function to each element of a list in parallel, up to `n` items at a time (default: num_cpus; override via ILO_PAR_MAP_CONCURRENCY). Returns `L (R b t)`: per-item Ok/Err in input order without short-circuit. Tree-walker implementation using std::thread::scope with chunked batches, following the get-many pattern. VM/Cranelift bail to tree via the existing bridge (is_tree_bridge_eligible). Large handler extracted into #[inline(never)] par_map_run per the ILO-289 dispatch-arm-size convention. Touches: src/builtins.rs, src/interpreter/mod.rs, src/parser/mod.rs, src/verify.rs, src/vm/mod.rs, SPEC.md, ai.txt, skills/ilo/ilo-builtins-io.md, examples/par-map.ilo. Includes 3 interpreter tests. Closes ILO-67. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Replace the wave-by-wave one-item-per-thread dispatch with an
auto-tuned chunking strategy: spawn at most `concurrency` threads,
each processing `ceil(len / concurrency)` items. This keeps
thread-creation overhead constant for large lists of small items.
Add cooperative cancellation via a shared `AtomicBool`: the first
worker to encounter a `RuntimeError` sets the flag; subsequent items
inside any worker are skipped and filled with a cancellation sentinel
`Err("par-map: cancelled due to earlier error")`.
Add three new unit tests (ILO-354):
- `par_map_large_list_chunking` — 100-item order-preservation check
- `par_map_error_cancels_remaining_workers` — cancellation on error
- `par_map_chunk_size_formula` — unit test for the auto-tuning formula
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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mini pc is reviewing this |
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Summary
ceil(len / concurrency)), spawning at mostconcurrencythreads each processing a slice of items. Constant thread overhead regardless of list length.AtomicBoolflag — first worker to hit aRuntimeErrorsets it; remaining unstarted items are skipped with aErr("par-map: cancelled due to earlier error")sentinel.par_map_large_list_chunking,par_map_error_cancels_remaining_workers,par_map_chunk_size_formula.Extends ILO-67 / PR #610.
Test plan
cargo test par_map— all 6 tests pass🤖 Generated with Claude Code