55 lines
2.7 KiB
Markdown
55 lines
2.7 KiB
Markdown
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# Cycle 4: Shutdown Fix + Bug-Inspired Tests — Development History
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> Commit: `cf61619` · 3 files · 161 insertions, 12 deletions
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---
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## Motivation
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Cycle 3 introduced thread parking, but created a new problem: `shutdown()` didn't unpark workers. Parked workers wouldn't notice the shutdown signal until their `park_timeout` expired, causing delayed shutdown. Additionally, studying bug reports from competitor projects (Ractor, Kameo, Actix) revealed specific failure modes worth testing in swactor.
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## Competitor Bug Analysis
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The 5 new tests were directly inspired by real bug reports from other actor frameworks:
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| Test | Inspired By | Bug |
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|------|-------------|-----|
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| `stats_snapshot_is_read_only` | Ractor #310 | `get_children()` was destructive — moved children out of supervisor |
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| `stats_under_load_do_not_interfere_with_processing` | General | Stats collection shouldn't slow down message processing |
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| `shutdown_wakes_parked_workers_immediately` | Cycle 3 regression | Parked workers must notice shutdown promptly |
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| `mt_send_after_run_delivers_to_running_actors` | Kameo #185 | Messages sent after `run()` weren't delivered during startup race |
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| `budget_respected_even_with_self_sends` | Actix #515 | Self-sends bypassed mailbox capacity, defeating backpressure |
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## Implementation
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### Shutdown Fix
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- `shutdown()` now iterates all workers and calls `unpark()` on each thread handle
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- Parked workers wake immediately and check the shutdown flag
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- Workers that aren't parked are unaffected (unpark is a no-op)
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### Bug-Inspired Tests
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Each test encodes a real bug class discovered in competitor frameworks, ensuring swactor doesn't have the same vulnerability.
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**Key files modified:** `src/runtime.rs`, `tests/runtime_api.rs`
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## Design Decisions
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- **Unpark-all on shutdown** rather than a dedicated shutdown condvar — simpler, reuses existing parking infrastructure from Cycle 3
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- **Bug-inspired testing methodology** — studying competitor bug trackers yields high-value test cases that target real failure modes, not theoretical ones
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## Tests Added
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5 new tests (52 → 57 total):
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- `stats_snapshot_is_read_only` — reading stats doesn't mutate runtime state (from Ractor #310)
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- `stats_under_load_do_not_interfere_with_processing` — stats don't affect message processing throughput
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- `shutdown_wakes_parked_workers_immediately` — validates fast shutdown with thread parking
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- `mt_send_after_run_delivers_to_running_actors` — messages sent after run() are delivered (from Kameo #185)
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- `budget_respected_even_with_self_sends` — self-sends don't bypass budget (from Actix #515)
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## Result
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- 57 tests pass
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- All workspace crates compile
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- Shutdown latency with parked workers reduced from up to 1ms to near-zero
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