fix:(llmrails): pre-initialize LLMRails.kb to prevent AttributeError on init failure

[octo-patch]

Fixes #1665

Problem

When LLMRails is initialized, it calls _init_kb() in a background thread via asyncio.run(). If the background thread fails (e.g., asyncio.run() raises a RuntimeError before the coroutine body starts), the thread exits silently — threading.Thread.join() does not propagate thread exceptions. As a result, self.kb is never set on the LLMRails instance.

Any subsequent access to self.kb (including self.runtime.register_action_param("kb", self.kb) at the end of __init__) then raises:

AttributeError: 'LLMRails' object has no attribute 'kb'

This has been reported for Python 3.12+ in LangGraph/LangChain integration scenarios.

Solution

Pre-initialize self.kb = None immediately before launching the background thread. This ensures:

1. The attribute always exists on the LLMRails instance, even if _init_kb() never runs.
2. Behavior is consistent with _init_kb() itself, which already sets self.kb = None as its very first statement before any conditional logic.

Testing

• Existing tests continue to pass (no functional logic changed).
• The fix is purely defensive initialization that mirrors what _init_kb() already does.

Signed-off-by: Octopus liyuan851277048@icloud.com

Summary by CodeRabbit

• Bug Fixes
  • Improved knowledge base initialization reliability to prevent potential startup failures.

[greptile-apps]

Greptile Summary

This PR adds a single defensive line self.kb = None before the background thread that runs _init_kb(), preventing an AttributeError when the thread fails silently (e.g., due to a nested event-loop RuntimeError in Python 3.12+ environments). The fix is minimal and correctly mirrors the first statement already inside _init_kb() itself.

Confidence Score: 5/5

This PR is safe to merge — it is a purely defensive one-line initialization with no functional change to the happy path.

The change adds self.kb = None before a background thread launch, mirroring the identical first statement already inside _init_kb(). No logic is altered for the success path; the failure path is strictly improved. No new risks introduced.

No files require special attention.

Important Files Changed

Filename	Overview
nemoguardrails/rails/llm/llmrails.py	Adds self.kb = None pre-initialization before the background thread launch to prevent AttributeError when the thread exits before setting the attribute; change is minimal, correct, and mirrors the first line of _init_kb().

Sequence Diagram

sequenceDiagram
    participant C as Caller
    participant R as LLMRails.__init__
    participant T as Background Thread
    participant K as _init_kb()

    C->>R: LLMRails(config, ...)
    R->>R: register_actions(llm_generation_actions)
    Note over R: self.kb = None  ← NEW (pre-init)
    R->>T: Thread(target=asyncio.run, args=(_init_kb(),)).start()
    T->>K: asyncio.run(_init_kb())
    alt _init_kb succeeds
        K->>K: self.kb = None
        K->>K: self.kb = KnowledgeBase(...)
        K->>K: kb.init() / kb.build()
        K-->>T: coroutine completes
        T-->>R: join() returns
        R->>R: register_action_param("kb", self.kb) ← kb is KnowledgeBase
    else _init_kb fails
        K--xT: exception swallowed by thread
        T-->>R: join() returns (silently)
        R->>R: register_action_param("kb", self.kb) ← kb is None (no AttributeError)
    end
    R-->>C: LLMRails instance returned

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[coderabbitai]

📝 Walkthrough

Walkthrough

The change initializes self.kb to None in LLMRails.__init__ before launching the asynchronous _init_kb operation. This ensures the attribute exists prior to registration and prevents AttributeError when accessing kb before async initialization completes.

Changes

Cohort / File(s)	Summary
KB Attribute Initialization nemoguardrails/rails/llm/llmrails.py	Initialize self.kb = None before async knowledge base initialization to prevent race condition where attribute is accessed before _init_kb completes.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Linked Issues check	✅ Passed	The PR directly addresses issue #1665 by pre-initializing self.kb=None before launching the background thread, which prevents AttributeError when asyncio.run() fails and _init_kb never runs.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the AttributeError issue in #1665; the PR only adds defensive initialization of self.kb and does not introduce unrelated modifications.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Test Results For Major Changes	✅ Passed	PR contains minor defensive initialization changes (+2 lines) fixing AttributeError. Existing tests continue to pass; no functional logic altered.
Title check	✅ Passed	The title accurately describes the main change: pre-initializing LLMRails.kb to prevent AttributeError on initialization failure.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Pouyanpi]

Thank you @octo-patch for fixing the issue👍🏻