Overview

Extends the centralized cleanup method to handle journey tracing state alongside core span cleanup. Fixes memory leak on natural completion path.

Problem Solved

Memory leak identified: Journey state (_first_token_emitted, _journey_prefill_hiwater) was not being cleaned up on natural completion path, only on explicit abort path.

Solution

Centralized all cleanup in _end_core_span_and_cleanup() with proper decoupling:

• Cleanup [Feature] Add monotonically increasing step counter to vLLM scheduler #1: Core spans (always runs, independent of flags)
• Cleanup [Feature] Add request journey event tracing to v1 scheduler #2: Journey state (only runs if _enable_journey_tracing=True)

Changes

Production Code (vllm/v1/core/sched/scheduler.py)

• Extended _end_core_span_and_cleanup() with decoupled cleanup logic
• Removed duplicate inline cleanup from finish_requests()
• Added comprehensive docstring explaining the two independent cleanup concerns

Tests (tests/v1/core/test_scheduler.py)

Added 4 comprehensive tests:

1. test_journey_state_created - Verify state initialization
2. test_journey_state_cleaned_on_finish - Explicit abort cleanup
3. test_journey_state_cleaned_on_completion - Natural completion cleanup ⭐ Critical test
4. test_no_state_leak - No accumulation over 20 iterations (focused unit test)

Test Results

✅ All 95 tests passing (4 new + 91 existing)
✅ No regressions
✅ Memory leak fixed
✅ Both termination paths verified

Key Design Principles

• Decoupling: Span cleanup NEVER gated behind feature flags
• Centralization: Single method handles all cleanup
• Idempotency: Safe to call multiple times
• Defensive: Cleanup runs even on exceptions

Part of Journey Tracing Initiative

This is PR #3 of 9 in the dual-stream journey tracing implementation plan:

• ✅ PR [Feature] Add monotonically increasing step counter to vLLM scheduler #1: Scheduler tracer initialization
• ✅ PR [Feature] Add request journey event tracing to v1 scheduler #2: Core span lifecycle management
• ✅ PR [Feature] Add CLI flag for journey tracing with OTEL integration #3: Journey state cleanup (this PR)
• 🔜 PR [Refactor] Use SpanAttributes constants for journey event attributes #4: Journey event emission
• 🔜 PR [Bugfix] Fix prefill progress tracking for chunked prefill preemption #5-9: API layer spans and cleanup

Review Notes

• Production code reviewed and approved by ChatGPT (2 rounds)
• Tests improved based on feedback: simpler, faster, more focused
• No breaking changes
• Backward compatible

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