Fix UnboundLocalError when DetokenizerManager constructor fails

[hnyls2002]

Motivation

When the DetokenizerManager constructor fails (e.g., due to HF API 429 rate limiting during AutoTokenizer.from_pretrained), the except block in run_detokenizer_process references manager before it is assigned, raising UnboundLocalError. This prevents SIGQUIT from reaching the parent process, leaving the server in a half-dead state — it accepts HTTP connections but returns 503 on /health_generate indefinitely until the test timeout (~10 minutes).

Example failure: https://github.com/sgl-project/sglang/actions/runs/23582037327/job/68670070787#step:7:5254

The server stays stuck returning 503 for ~10 minutes because SIGQUIT never fires:

[2026-03-26 08:44:08] INFO: 127.0.0.1:38764 - "GET /health_generate HTTP/1.1" 503 Service Unavailable
[2026-03-26 08:44:18] INFO: 127.0.0.1:46050 - "GET /health_generate HTTP/1.1" 503 Service Unavailable
... (repeats for ~10 minutes)
[2026-03-26 08:52:38] INFO: 127.0.0.1:39568 - "GET /health_generate HTTP/1.1" 503 Service Unavailable
TimeoutError: Server failed to start within the timeout period

Root cause in the logs:

DetokenizerManager hit an exception:
  ...
  httpx.HTTPStatusError: Client error '429 Too Many Requests'
  ...
  OSError: Unable to load vocabulary from file.

Process Process-2:
  UnboundLocalError: local variable 'manager' referenced before assignment

Modification

Initialize manager = None before the try block and guard the maybe_clear_socket_mapping() call with a None check, so send_signal(SIGQUIT) always executes.

Test plan

• Existing CI (no behavioral change for the success path)

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the robustness of the server's error handling mechanism. It resolves a critical issue where failures during the DetokenizerManager's initialization could lead to an UnboundLocalError, preventing proper signal propagation and leaving the server in a half-dead state. The changes ensure that the server gracefully exits and cleans up resources even when core components fail to start, improving overall system stability.

Highlights

• Error Handling Fix: Addressed an UnboundLocalError that occurred when the DetokenizerManager constructor failed, preventing the SIGQUIT signal from being sent to the parent process and leaving the server in an unresponsive state.
• Robust Shutdown: Ensured that the SIGQUIT signal is always sent to the parent process upon DetokenizerManager initialization failure by initializing manager to None and adding a null check before attempting to clear socket mappings.

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[gemini-code-assist]

Code Review

This pull request improves the robustness of the run_detokenizer_process function by initializing the manager variable to None and adding a None check before attempting to call manager.maybe_clear_socket_mapping() within the exception handler. This prevents potential AttributeError if the manager fails to initialize. The review suggests a further improvement to error handling by wrapping the maybe_clear_socket_mapping() call in its own try...except block to ensure the critical parent_process.send_signal(signal.SIGQUIT) is always executed, even if the cleanup operation itself raises an exception, thus preventing a half-dead server state.

[gemini-code-assist]

To improve robustness, it's advisable to wrap the cleanup logic in a try...except block. This ensures that parent_process.send_signal(signal.SIGQUIT) is always executed, even if manager.maybe_clear_socket_mapping() were to raise an unexpected exception. The main goal is to prevent the server from entering a half-dead state, so guaranteeing the signal is sent is critical.

Suggested change

	if manager is not None:
	manager.maybe_clear_socket_mapping()
	if manager is not None:
	try:
	manager.maybe_clear_socket_mapping()
	except Exception as e_cleanup:
	logger.error(f"Error during detokenizer cleanup: {e_cleanup}")

[hnyls2002]

/tag-and-rerun-ci