[https://nvbugs/6461799][fix] Import MpiPoolSession from its source module…

[trtllm-agent]

Summary

• Root cause: tests/test_common/session_reuse.py monkey-patches MpiPoolSession in the tensorrt_llm.executor.proxy module namespace with a factory function, so isinstance(self.mpi_session, MpiPoolSession) at proxy.py:576 raises TypeError: isinstance() arg 2 must be a type because the second argument is a function, not a class.
• Fix: Import MpiPoolSession from its source module (tensorrt_llm.llmapi.mpi_session) at the use site so the class reference is resolved fresh from the source module (immune to attribute-level monkeypatching in tensorrt_llm.executor.proxy); leaves the constructor-call site at proxy.py:130 unchanged so session-reuse still intercepts pool creation.
• Automated fix generated by repair-bot

Test plan

• Verify fix on the same GPU type as the original failure
• Check for regressions in related tests

Links

• Bug: https://nvbugs/6461799

Summary by CodeRabbit

• Bug Fixes

  • Improved executor worker startup compatibility in runtime-configured environments.
  • Enhanced reliability when launching workloads through customized execution setups.

• Chores

  • Strengthened internal validation and testing support without changing public APIs or standard execution behavior.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between e158837 and 158d7e1.

📒 Files selected for processing (1)

• tensorrt_llm/executor/proxy.py

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📝 Walkthrough

Walkthrough

_start_executor_workers() now locally re-imports MpiPoolSession immediately before its isinstance check, allowing test monkey-patching of the source module’s class reference to be respected.

Changes

MpiPoolSession type-check handling

Layer / File(s)	Summary
Runtime session type resolution tensorrt_llm/executor/proxy.py	_start_executor_workers() re-imports MpiPoolSession locally before checking self.mpi_session.

Estimated code review effort: 2 (Simple) | ~5 minutes

Possibly related PRs

• NVIDIA/TensorRT-LLM#16496: Updates the same code path with a local MpiPoolSession re-import for test monkey-patching.
• NVIDIA/TensorRT-LLM#16411: Modifies the same MpiPoolSession type-check logic in _start_executor_workers().
• NVIDIA/TensorRT-LLM#16417: Adjusts the same session type-check path for monkey-patched test sessions.

Suggested reviewers: asfiyab-nvidia

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title matches the bug fix and uses the required ticket/type format, with the main change clearly stated.
Description check	✅ Passed	The description includes a clear summary, test plan, and linked bug, covering the template’s required information well enough.
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

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• Create PR with unit tests

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[tongyuantongyu]

Close in favor of #16444.