Shard rate limiters and reuse broadcast scratch to cut worker lock contention

[wksantiago]

Fixes #152. Shard rate limiters and reuse broadcast scratch to cut worker lock contention.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 0da50d6b-a91b-4cd7-bd6c-a69eaabccd33

📥 Commits

Reviewing files that changed from the base of the PR and between 666f059 and 06fd4a5.

📒 Files selected for processing (3)

• src/main.zig
• src/rate_limiter.zig
• src/subscriptions.zig

Walkthrough

The rate limiters now use 16 independently locked shards for bucket operations and cleanup. Subscription matching reuses thread-local pending-write and deduplication containers instead of allocating them per broadcast.

Changes

Rate limiter sharding

Layer / File(s)	Summary
Connection limiter shard operations src/rate_limiter.zig	ConnectionLimiter routes per-IP checks, updates, removals, cleanup, and statistics through shard-local mutexes and maps.
Event limiter shard operations src/rate_limiter.zig	EventRateLimiter applies token-bucket updates and cleanup per shard, with test helpers aggregating state across shards. Tests use those helpers for cleanup assertions.

Subscription matching scratch reuse

Layer / File(s)	Summary
Reusable matching state src/subscriptions.zig	forEachMatching clears and reuses thread-local pending-write and deduplication containers across calls.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• privkeyio/wisp#79: Both changes modify EventRateLimiter bucket storage and token-bucket cleanup behavior.

Poem

A rabbit counts shards in a moonlit array,
While buckets hop safely through locks on their way.
Broadcasts reuse scratch with a swift little cheer,
No fresh lists to nibble through year after year.
Thump-thump, the limiters and messages run bright!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately reflects the two main changes: sharding rate limiters and reusing broadcast scratch to reduce contention.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/worker-lock-contention

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