fix: Add thread-safe initialization to _DefaultLoadCalc singleton

[darshankparmar]

Summary by CodeRabbit

• Bug Fixes
  • Improved thread-safety in worker load calculations to prevent race conditions and ensure more stable performance under concurrent load.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Thread-safety improvements were added to the _DefaultLoadCalc singleton class in the worker module by introducing a threading lock and implementing double-checked locking pattern during instance initialization to prevent race conditions.

Changes

Cohort / File(s)	Summary
Thread-safe singleton initialization livekit-agents/livekit/agents/worker.py	Added class-level _instance_lock = threading.Lock() attribute and wrapped singleton instance creation in get_load() method with lock acquisition and null-check guarding to ensure thread-safe initialization

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A lock to guard our singleton's creation,
Double-checking for thread coordination,
No race conditions shall we see,
Safely shared, harmoniously!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding thread-safe initialization to the _DefaultLoadCalc singleton through lock-based synchronization.

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✨ Finishing touches

• 📝 Generate docstrings

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📜 Recent review details

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between a9cdddd and 3076932.

📒 Files selected for processing (1)

• livekit-agents/livekit/agents/worker.py

🧰 Additional context used

📓 Path-based instructions (1)

**/*.py

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Files:

• livekit-agents/livekit/agents/worker.py

🧠 Learnings (1)

📚 Learning: 2026-01-22T03:28:16.289Z

Learnt from: longcw
Repo: livekit/agents PR: 4563
File: livekit-agents/livekit/agents/beta/tools/end_call.py:65-65
Timestamp: 2026-01-22T03:28:16.289Z
Learning: In code paths that check capabilities or behavior of the LLM processing the current interaction, prefer using the activity's LLM obtained via ctx.session.current_agent._get_activity_or_raise().llm instead of ctx.session.llm. The session-level LLM may be a fallback and not reflect the actual agent handling the interaction. Use the activity LLM to determine capabilities and to make capability checks or feature toggles relevant to the current processing agent.

Applied to files:

• livekit-agents/livekit/agents/worker.py

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• GitHub Check: type-check (3.13)
• GitHub Check: type-check (3.9)
• GitHub Check: unit-tests

🔇 Additional comments (1)

livekit-agents/livekit/agents/worker.py (1)

81-109: Thread-safe singleton initialization looks solid.

Double-checked locking here prevents the race without adding overhead to steady-state reads.

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