chore(legacy): remove unused legacy plugin loader and C-ABI nyash-file plugin; unify plugin headers to TypeBox v2
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# Async Task System — Phased Plan (P1–P3)
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## Phase 1: Foundations (stabilize + timeouts)
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- FutureBox: switch to Mutex+Condvar (done).
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- Await: poll scheduler + timeout gate in VM and JIT (done; unify to Result.Err in P3).
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- env.future.spawn_instance: enqueue via Scheduler; fallback sync if no scheduler (done).
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- Safepoint: ensure env.runtime.checkpoint is emitted around await (Lowerer rule).
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- Smokes: async-await-min; async-spawn-instance (safe form, no env).
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- Acceptance:
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- No hangs (await respects timeout); CPU near idle while waiting.
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- VM/JIT pass basic smokes; lingering processes do not remain.
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## Phase 2: TaskGroup & CancellationToken
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- Types:
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- CancellationToken { cancel(), is_cancelled() } idempotent; parent→child propagation only.
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- TaskGroup Box { spawn(fn)->Future, cancelAll(), joinAll() }, owns token; fini enforces cancel→join.
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- API:
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- nowait sugar targets current TaskGroup.
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- Unsafe detached spawn hidden behind unsafe_spawn_detached() and verifier checks.
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- VM implementation:
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- Extend scheduler to accept token; tasks periodically check token or are cancelled at await.
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- Group registry per scope; insert fini hooks in function epilogues and Main.
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- JIT/EXE:
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- NyRT shims accept optional token handle; if missing, use current group’s token.
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- Smokes:
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- spawn_cancel_on_scope_exit; nested_groups; lifo_join_order.
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- Acceptance:
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- Parent exit cancels and joins children deterministically (LIFO); no leaks per leak tracker.
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## Phase 3: Error Semantics & Unification
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- Future.await returns Result<T, Err> (Timeout/Cancelled/Panic) consistently (VM/JIT).
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- Remove 0/None fallbacks; map shims to Result at Nyash layer.
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- Lowerer verifies checkpoints around await; add verifier rule.
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- Observability: minimal counters and optional traces.
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- Smokes:
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- await_timeout distinct from cancel; panic_propagation; wakeup_race (no double resolve).
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- Acceptance:
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- Consistent error surface; result handling identical across VM/JIT/EXE.
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## Test Matrix & CI
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- Backends: {vm, jit, aot} × Modes: {default, strict}.
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- Smokes kept minimal; time‑bounded via timeout(1) wrapper.
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- CPU spin test: ensure idle waiting; measured via time/ps (best‑effort).
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## Migration & Compatibility
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- Keep env.future.spawn_instance during transition; TaskGroup.spawn preferred.
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- nowait sugar remains; mapped to TaskGroup.spawn.
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- Document flags: NYASH_AWAIT_MAX_MS, NYASH_SCHED_*.
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## Files & Ownership
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- Spec & Plan live here; updates linked from CURRENT_TASK.md.
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- Code changes limited to runtime/{scheduler,global_hooks}, boxes/future, jit/extern/async, lowerer await rules.
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# Async Task System (Structured Concurrency) — Overview
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Goal: A safe, structured, and portable async task system that runs end‑to‑end across Nyash code → MIR → VM → JIT/EXE.
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- Default is safe: tasks are scoped to an owning group; when the owner ends, children cancel and join.
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- Everything is Box: TaskGroup and Future are Boxes; user APIs are Box methods; MIR uses BoxCall.
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- No new MIR ops required: use BoxCall/PluginInvoke consistently; safepoints are inserted around await.
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- Deterministic exits: parent exit triggers cancelAll → joinAll on children (LIFO), eliminating leaks.
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This folder contains the spec, phase plan, and test plan:
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- SPEC.md: User API, Box contracts, MIR/VM/JIT mapping, ABI, error semantics.
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- PLAN.md: Phased rollout (P1–P3), acceptance gates and checklists.
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# Async Task System — SPEC
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Scope: Define a structured concurrency model for Nyash with TaskGroup and Future as Boxes. Implementable across VM and JIT/EXE without adding new MIR instructions.
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## User‑Facing API (Everything is Box)
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Box TaskGroup
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- spawn(fn: () -> T) -> Future<T>
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- cancelAll() -> void
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- joinAll() -> void
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- fini: must run cancelAll() then joinAll() (LIFO order) to ensure structured shutdown.
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Box Future<T>
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- await(timeout_ms?: int) -> Result<T, Err>
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- Ok(value)
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- Err(Timeout) | Err(Cancelled) | Err(Panic)
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- cancel() -> void (idempotent)
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Sugar
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- nowait v = expr is sugar for: let g = current_group(); v = g.spawn(lambda: expr)
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Default Ownership
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- An implicit TaskGroup is created per function scope and for Main. It owns tasks spawned in that scope.
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- Leaving the scope triggers cancelAll→joinAll on its group (LIFO), unless tasks were moved to a longer‑lived group explicitly.
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Detachment (discouraged)
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- unsafe_spawn_detached(fn) only in advanced modules. Verifier should disallow use in normal code paths.
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## MIR Mapping
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- No new MIR instructions. Use existing BoxCall/PluginInvoke forms.
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- TaskGroup.spawn → BoxCall on TaskGroup Box, returns Future Box.
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- Future.await → BoxCall on Future Box with optional timeout parameter.
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- Lowerer inserts safepoint around await: ExternCall env.runtime.checkpoint before and after the await call.
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Example Lowering (high level)
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- AST: nowait fut = arr.length()
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- MIR (normalized):
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- recv = … (arr)
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- mname = Const("length")
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- fut = ExternCall iface="env.future", method="spawn_instance", args=[recv, mname]
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- v = BoxCall Future.await(fut, timeout_ms?)
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Note: In the final API, TaskGroup.spawn replaces env.future.spawn_instance, but the MIR contract remains BoxCall/ExternCall‑based.
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## VM Semantics
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- Scheduler: SingleThreadScheduler initially; spawn enqueues closure in FIFO. safepoint_and_poll() runs due tasks.
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- Future: implemented with Mutex+Condvar; set_result notifies; await waits with optional timeout; on cancel/timeout, returns Result.Err.
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- CancellationToken: parent→child propagation only, idempotent cancel().
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- TaskGroup: holds token and child registry; fini enforces cancelAll→joinAll (LIFO).
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## JIT/EXE Semantics
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- NyRT C‑ABI Shims:
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- nyash.future.spawn_method_h(type_id, method_id, argc, recv_h, vals*, tags*) -> i64 (Future handle)
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- nyash.future.spawn_instance3_i64(a0, a1, a2, argc) -> i64 (Future handle, by name/first args)
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- nyash.future.await_h(handle, timeout_ms?) -> i64/handle (Result encoding handled at Nyash layer)
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- Await shim must poll safepoints and honor timeout; returns 0 or sentinel; Nyash layer maps to Result.Err.*
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## Errors & Results
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- Distinguish Timeout vs Cancelled vs Panic.
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- Logging: concise, off by default; env flags can enable traces.
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- No silent fallback: unimplemented paths error early with clear labels.
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## GC & Safepoints
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- Lowerer must emit env.runtime.checkpoint immediately before and after await calls.
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- Scheduler.poll runs at checkpoints; long loops should explicitly insert checkpoints.
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## Configuration
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- NYASH_AWAIT_MAX_MS (default 5000) — global default timeout for await when not specified.
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- NYASH_SCHED_POLL_BUDGET — tasks per poll, default 1.
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- NYASH_SCHED_TRACE — prints poll/move/ran counts when 1.
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## Security & Determinism
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- Structured shutdown prevents orphan tasks after parent exit.
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- LIFO joinAll reduces deadlock surfaces.
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- Detached tasks are explicit and rare.
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