[BugFix] Fix async scheduling + reasoning with struct output (#31332)

Signed-off-by: Nick Hill <nickhill123@gmail.com>

tests/v1/entrypoints/llm/test_struct_output_generate.py

@@ -608,7 +608,7 @@ Make the response as short as possible.
 
 
 @pytest.mark.parametrize(
-    "model_name, backend, tokenizer_mode, reasoning_parser, speculative_config",  # noqa: E501
+    "model_name, backend, tokenizer_mode, reasoning_parser, speculative_config, async_scheduling",  # noqa: E501
     [
         (
             "deepseek-ai/DeepSeek-R1-Distill-Qwen-1.5B",
@@ -616,8 +616,10 @@ Make the response as short as possible.
             "auto",
             "deepseek_r1",
             NGRAM_SPEC_CONFIG,
+            False,
         ),
-        ("Qwen/Qwen3-1.7B", "xgrammar", "auto", "deepseek_r1", None),
+        ("Qwen/Qwen3-1.7B", "xgrammar", "auto", "deepseek_r1", None, False),
+        ("Qwen/Qwen3-1.7B", "xgrammar", "auto", "deepseek_r1", None, True),
     ],
 )
 def test_structured_output_with_reasoning_matrices(
@@ -626,6 +628,7 @@ def test_structured_output_with_reasoning_matrices(
     reasoning_parser: str,
     model_name: str,
     speculative_config: dict[str, Any] | None,
+    async_scheduling: bool,
 ):
     if current_platform.is_tpu() and speculative_config:
         pytest.skip("TPU does not support speculative decoding")
@@ -646,6 +649,7 @@ def test_structured_output_with_reasoning_matrices(
         ),
         tokenizer_mode=tokenizer_mode,
         speculative_config=speculative_config,
+        async_scheduling=async_scheduling,
     )
     tokenizer = llm.get_tokenizer()
     reasoner = ReasoningParserManager.get_reasoning_parser(reasoning_parser)(

tests/v1/structured_output/test_reasoning_structured_output.py

@@ -71,6 +71,7 @@ class TestReasoningStructuredOutput:
         request.prompt_token_ids = [1, 2, 3, 4, 5]
         request.all_token_ids = [1, 2, 3, 4, 5, 6, 7, 8]
         request.num_computed_tokens = 5
+        request.num_output_placeholders = 0
         return request
 
     def test_should_fill_bitmask_with_enable_in_reasoning(

vllm/v1/structured_output/__init__.py

@@ -339,8 +339,9 @@ class StructuredOutputManager:
             return True
 
         # Check if reasoning ends in *this* step
+        delta_from = request.num_computed_tokens - request.num_output_placeholders
         if self.reasoner.is_reasoning_end_streaming(
-            request.all_token_ids, request.all_token_ids[request.num_computed_tokens :]
+            request.all_token_ids, request.all_token_ids[delta_from:]
         ):
             # Reasoning just ended, so we shouldn't advance til
             # next pass