perf(runtime): drain nextTick queue with VecDeque::pop_front (was O(n²))

[proggeramlug]

One of the #6084 server-scalability quadratics.

Problem

QUEUED_MICROTASKS (the process.nextTick queue) was a Vec drained with queue.remove(0), which is O(n) per job — so draining a burst of n nextTick jobs (common under Node stream / 'readable' scheduling) memmoves ~n²/2 entries.

Fix

Use VecDeque with push_back / pop_front for O(1) drain — the same structure the promise TASK_QUEUE already uses.

Behavior

Unchanged: FIFO order and same-drain visibility of jobs enqueued during the drain. Verified vs node --experimental-strip-types: nextTick ordering (1,2,3 incl. a job queued inside a job) and a 1000-job burst both match.

Summary by CodeRabbit

• Performance
  • Improved microtask handling for queueMicrotask and process.nextTick, reducing queue draining overhead and making scheduling more efficient.
• Bug Fixes
  • Smoothed out queue processing behavior by using a more efficient first-in, first-out approach.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: c3f4e56d-130b-4839-b100-90d42cafdd8f

📥 Commits

Reviewing files that changed from the base of the PR and between c78c20b and afc4fd5.

📒 Files selected for processing (1)

• crates/perry-runtime/src/builtins/globals.rs

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📝 Walkthrough

Walkthrough

The internal microtask queue backing queueMicrotask/process.nextTick is changed from a Vec to a VecDeque. Enqueue operations use push_back, dequeue operations use pop_front instead of remove(0), and related unit tests are updated accordingly.

Changes

Microtask Queue VecDeque Migration

Layer / File(s)	Summary
Queue type and enqueue/dequeue implementation crates/perry-runtime/src/builtins/globals.rs	QUEUED_MICROTASKS is redefined as RefCell<VecDeque<QueuedMicrotask>>, enqueue uses push_back, and draining uses pop_front instead of remove(0).
Test updates for VecDeque crates/perry-runtime/src/builtins/globals.rs	Unit tests seed the queue with push_back() and inspect the front element with front() instead of push()/first().

Estimated code review effort: 1 (Trivial) | ~5 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the runtime performance change to the nextTick queue and matches the implemented VecDeque drain fix.
Description check	✅ Passed	The description covers the problem, fix, behavior, and verification, though it does not follow the template's explicit section headings.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/6084-nexttick-vecdeque

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