[biswapanda]

Overview

Establish a bounded SGLang decode and aggregated-worker cancellation lifecycle that works before the first output for single-sample requests while keeping internal engine IDs separate from caller-visible response IDs.

Details

• wait for request registration and dispatch before the first abort
• detach and strongly own bounded abort retries so stream cleanup is never held open
• cancel outstanding retry tasks before engine shutdown
• preserve public response IDs across native and text output paths
• advertise versioned runtime capability metadata
• fail closed to response-ID cancellation for true parallel sampling (n > 1) and native batch inputs because SGLang replaces normalized child IDs with unrelated UUIDs and exposes no group-abort API
• expand and supersede the cancellation foundation proposed in fix(sglang): cancel decode requests before the first engine response #14370

Stack

• Base: main
• Next: fix(sglang): abort disaggregated prefill requests on cancellation #14782

Architecture

flowchart LR
    C[Client] --> F[Dynamo frontend]
    F --> W["SGLang decode / aggregated worker"]
    W --> I[Internal engine request ID]
    I --> E[SGLang engine]
    W --> M[Cancellation monitor]
    M --> G{Stable engine ID?}
    G -->|Single sample or beam| R[Registration and dispatch state]
    R --> A[Ordered abort with bounded retries]
    G -->|True n > 1 or native batch| O[First observed child response ID]
    O --> B[Response-ID abort fallback]
    A --> E
    B --> E
    W --> P[Caller-visible response ID]
    P --> C

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Sequence

sequenceDiagram
    participant C as Client
    participant W as Decode worker
    participant R as Request registry
    participant E as SGLang engine
    C->>W: Submit generation request
    W->>E: Generate with internal request ID
    C--xW: Disconnect or stop
    alt Stable single-sample or beam request ID
        W->>R: Wait for request registration
        R-->>W: Request is registered
        W->>R: Wait for dispatch completion
        R-->>W: Dispatch observed or wait bounded
        W->>E: Abort internal request ID
        opt Request remains registered
            W->>E: Retry abort within bounded policy
        end
    else True n > 1 parallel sampling
        Note over W,E: SGLang regenerates unrelated child UUIDs
        E-->>W: First child response exposes its actual UUID
        W->>E: Abort the observed response UUID
    end
    W-->>C: End stream after bounded cleanup

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Where should the reviewer start?

• components/src/dynamo/sglang/request_handlers/cancellation.py for the cancellation lifecycle and bounded cleanup
• components/src/dynamo/sglang/request_handlers/llm/decode_handler.py for request identity, the parallel-sampling guard, and stream integration
• components/src/dynamo/sglang/tests/test_sglang_decode_cancellation.py for lifecycle regression coverage

Validation

• 443 tests across every Python test file changed by the final stacked head passed after the latest-main rebase
• focused mypy reached only the two known local environment stub gaps (dynamo._core.backend and types-PyYAML), with no changed-code errors
• all touched-file pre-commit hooks passed
• cargo clippy for dynamo-llm with warnings denied passed
• every rebased commit is cryptographically signed and GitHub-verified
• thermo-nuclear code-quality review approved
• adversarial Claude Opus 1M review findings addressed
• final independent code review approved

Related Issues

Relates to #13691

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Walkthrough

The SGLang integration adds cancellation and shutdown coordination, ordered disaggregated-prefill compatibility detection, router-owned request IDs, cancellation-aware stream handling, response-ID remapping, and comprehensive tests.

Changes

SGLang cancellation flow

Layer / File(s)	Summary
Compatibility and request identity contracts components/src/dynamo/sglang/_compat.py, components/src/dynamo/sglang/engine_generate.py	The code detects ordered cancellation support and assigns internal SGLang request IDs. Native requests always use the supplied internal ID.
Cancellation monitoring and handler wiring components/src/dynamo/sglang/request_handlers/cancellation.py, components/src/dynamo/sglang/request_handlers/handler_base.py	CancellationMixin manages registration, aborts, retries, stream draining, shutdown, and cleanup. BaseWorkerHandler uses the mixin and records compatibility support.
Decode request and stream integration components/src/dynamo/sglang/request_handlers/llm/decode_handler.py	Decode paths pass generated IDs through native, aggregated, and disaggregated streams. Streams drain after cancellation, and native responses preserve caller-visible IDs without mutating the original payload.
Cancellation and request identity validation components/src/dynamo/sglang/tests/test_sglang_decode_cancellation.py, components/src/dynamo/sglang/tests/test_sglang_decode_handler.py, components/src/dynamo/sglang/tests/test_sglang_unit.py	Tests cover cancellation timing, shutdown, retries, races, cleanup, stream draining, request-ID ownership, response-ID remapping, and compatibility detection.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Merge Risk: 🔵 Low · up to 48305

Text-stream clients may receive an internal request ID, and a cleanup regression could leave one CI test hanging. These localized issues should be corrected or explicitly accepted before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.95% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 76 functions across 8 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly identifies the main change: aborting SGLang decode requests cancelled before the first token.
Description check	✅ Passed	The description includes the required overview, details, reviewer starting points, and related issue information. It also provides architecture, sequence, and validation details.

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Actionable comments posted: 2

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Inline comments:
In `@components/src/dynamo/sglang/request_handlers/llm/decode_handler.py`:
- Line 646: Update _process_text_stream so each yielded text-stream chunk uses
the public request ID from context.id(), rather than copying the internal SGLang
ID from meta_info["id"]; preserve the existing native-path ID behavior and all
other chunk fields.

In `@components/src/dynamo/sglang/tests/test_sglang_decode_cancellation.py`:
- Around line 28-29: Add the existing pytest timeout marker with a five-second
limit to test_cancellation_monitor_rechecks_shutdown_after_cleanup, matching the
other wait-related tests in the module.

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📥 Commits

Reviewing files that changed from the base of the PR and between 11b85b9 and 48305f7.

📒 Files selected for processing (8)

• components/src/dynamo/sglang/_compat.py
• components/src/dynamo/sglang/engine_generate.py
• components/src/dynamo/sglang/request_handlers/cancellation.py
• components/src/dynamo/sglang/request_handlers/handler_base.py
• components/src/dynamo/sglang/request_handlers/llm/decode_handler.py
• components/src/dynamo/sglang/tests/test_sglang_decode_cancellation.py
• components/src/dynamo/sglang/tests/test_sglang_decode_handler.py
• components/src/dynamo/sglang/tests/test_sglang_unit.py

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[KrishnanPrash]

Pre-approving, please take a look at the comments.