[Core][Performance] Add XGrammar support for guided decoding and set it as default

docs/source/conf.py

@@ -112,6 +112,7 @@ def setup(app):
     "tensorizer",
     "pynvml",
     "outlines",
+    "xgrammar,"
     "librosa",
     "soundfile",
     "gguf",

requirements-common.txt

@@ -19,6 +19,7 @@ prometheus-fastapi-instrumentator >= 7.0.0
 tiktoken >= 0.6.0  # Required for DBRX tokenizer
 lm-format-enforcer >= 0.10.9, < 0.11
 outlines >= 0.0.43, < 0.1
+xgrammar
 typing_extensions >= 4.10
 filelock >= 3.16.1 # need to contain https://github.com/tox-dev/filelock/pull/317
 partial-json-parser # used for parsing partial JSON outputs

tests/entrypoints/llm/test_guided_generate.py

@@ -159,3 +159,30 @@ def test_validation_against_both_guided_decoding_options(sample_regex, llm):
                      sampling_params=sampling_params,
                      use_tqdm=True,
                      guided_options_request=dict(guided_regex=sample_regex))
+
+
+@pytest.mark.skip_global_cleanup
+def test_guided_json_object(llm):
+    sampling_params = SamplingParams(
+        temperature=1.0,
+        max_tokens=100,
+        guided_decoding=GuidedDecodingParams(json_object=True))
+
+    outputs = llm.generate(
+        prompts=("Generate a JSON object describing a person with name "
+                 "and age for John Smith who is 31 years old."),
+        sampling_params=sampling_params,
+        use_tqdm=True)
+
+    assert outputs is not None
+    for output in outputs:
+        assert output is not None
+        assert isinstance(output, RequestOutput)
+
+        generated_text = output.outputs[0].text
+        print(generated_text)
+        assert generated_text is not None
+
+        # Parse to verify it is valid JSON
+        parsed_json = json.loads(generated_text)
+        assert isinstance(parsed_json, dict)

tests/model_executor/test_guided_processors.py

@@ -36,7 +36,8 @@ def test_guided_logits_processors(sample_regex, sample_json_schema):
 
 
 @pytest.mark.asyncio
-@pytest.mark.parametrize("backend", ["outlines", "lm-format-enforcer"])
+@pytest.mark.parametrize("backend",
+                         ["outlines", "lm-format-enforcer", "xgrammar"])
 async def test_guided_logits_processor_black_box(backend: str, sample_regex,
                                                  sample_json_schema):
     tokenizer = AutoTokenizer.from_pretrained('HuggingFaceH4/zephyr-7b-beta')

vllm/config.py

@@ -1789,15 +1789,15 @@ class PoolerConfig:
 
     step_tag_id: Optional[int] = None
     """
-    If set, only the score corresponding to the ``step_tag_id`` in the 
+    If set, only the score corresponding to the ``step_tag_id`` in the
     generated sentence should be returned. Otherwise, the scores for all tokens
     are returned.
     """
 
     returned_token_ids: Optional[List[int]] = None
     """
-    A list of indices for the vocabulary dimensions to be extracted, 
-    such as the token IDs of ``good_token`` and ``bad_token`` in the 
+    A list of indices for the vocabulary dimensions to be extracted,
+    such as the token IDs of ``good_token`` and ``bad_token`` in the
     ``math-shepherd-mistral-7b-prm`` model.
     """
 
@@ -2031,11 +2031,12 @@ def get_served_model_name(model: str,
 class DecodingConfig:
     """Dataclass which contains the decoding strategy of the engine"""
 
-    # Which guided decoding algo to use. 'outlines' / 'lm-format-enforcer'
-    guided_decoding_backend: str = 'outlines'
+    # Which guided decoding algo to use.
+    # 'outlines' / 'lm-format-enforcer' / 'xgrammar'
+    guided_decoding_backend: str = 'xgrammar'
 
     def __post_init__(self):
-        valid_guided_backends = ['outlines', 'lm-format-enforcer']
+        valid_guided_backends = ['outlines', 'lm-format-enforcer', 'xgrammar']
         backend = self.guided_decoding_backend
         if backend not in valid_guided_backends:
             raise ValueError(f"Invalid guided_decoding_backend '{backend},"
@@ -2222,7 +2223,7 @@ class CompilationConfig(BaseModel):
             from Python, functions can also be passed directly via Python object
             constructor, e.g. `CompilationConfig(inductor_passes={"a": func})`
         - custom inductor passes: see PassConfig for more details
-    
+
     Why we have different sizes for cudagraph and inductor:
     - cudagraph: a cudagraph captured for a specific size can only be used
         for the same size. We need to capture all the sizes we want to use.

vllm/engine/arg_utils.py

@@ -168,7 +168,7 @@ class EngineArgs:
     scheduler_delay_factor: float = 0.0
     enable_chunked_prefill: Optional[bool] = None
 
-    guided_decoding_backend: str = 'outlines'
+    guided_decoding_backend: str = 'xgrammar'
     # Speculative decoding configuration.
     speculative_model: Optional[str] = None
     speculative_model_quantization: Optional[str] = None
@@ -364,11 +364,12 @@ def add_cli_args(parser: FlexibleArgumentParser) -> FlexibleArgumentParser:
         parser.add_argument(
             '--guided-decoding-backend',
             type=str,
-            default='outlines',
-            choices=['outlines', 'lm-format-enforcer'],
+            default='xgrammar',
+            choices=['outlines', 'lm-format-enforcer', 'xgrammar'],
             help='Which engine will be used for guided decoding'
             ' (JSON schema / regex etc) by default. Currently support '
-            'https://github.com/outlines-dev/outlines and '
+            'https://github.com/outlines-dev/outlines,'
+            'https://github.com/mlc-ai/xgrammar, and '
             'https://github.com/noamgat/lm-format-enforcer.'
             ' Can be overridden per request via guided_decoding_backend'
             ' parameter.')

vllm/engine/async_llm_engine.py

@@ -1,4 +1,5 @@
 import asyncio
+import copy
 import time
 import weakref
 from functools import partial
@@ -504,7 +505,8 @@ async def add_request_async(
                 sampling_params=params,
                 tokenizer=await self.get_tokenizer_async(lora_request),
                 default_guided_backend=self.decoding_config.
-                guided_decoding_backend)
+                guided_decoding_backend,
+                model_config=self.model_config)
 
         self._add_processed_request(
             request_id=request_id,
@@ -525,22 +527,30 @@ async def check_health_async(self) -> None:
 
 async def build_guided_decoding_logits_processor_async(
         sampling_params: SamplingParams, tokenizer: AnyTokenizer,
-        default_guided_backend: str) -> SamplingParams:
+        default_guided_backend: str,
+        model_config: ModelConfig) -> SamplingParams:
     """Constructs logits processors based on the guided_decoding,
     logits_bias, and allowed_token_ids fields in sampling_params. Deletes
     those fields and adds the constructed logits processors to the
     logits_processors field. Modifies sampling params in-place and returns
     the modified sampling params."""
-    if (guided_decoding := sampling_params.guided_decoding) is None:
+    if sampling_params.guided_decoding is None:
         return sampling_params
 
+    # Defensively copy sampling params since guided decoding logits
+    # processors can have different state for each request
+    sampling_params = copy.copy(sampling_params)
+    guided_decoding = sampling_params.guided_decoding
+
     logger.debug("Building guided decoding logits processor. "
                  "Params: %s", guided_decoding)
 
     guided_decoding.backend = guided_decoding.backend or default_guided_backend
 
     processor = await get_guided_decoding_logits_processor(
-        guided_params=guided_decoding, tokenizer=tokenizer)
+        guided_params=guided_decoding,
+        tokenizer=tokenizer,
+        model_config=model_config)
 
     if processor:
         if sampling_params.logits_processors is None:

vllm/engine/llm_engine.py

@@ -1,3 +1,4 @@
+import copy
 import time
 from collections import Counter as collectionsCounter
 from collections import deque
@@ -1023,9 +1024,9 @@ def _update_num_computed_tokens_for_multi_step_prefill(
         This function updates num_computed_tokens for prompt sequences
         when Multi-Step is enabled.
 
-        seq_group: SequenceGroup to update the num_computed_tokens for. 
+        seq_group: SequenceGroup to update the num_computed_tokens for.
         seq_group_meta: Metadata of the given SequenceGroup.
-        is_first_step_output: Optional[bool] - 
+        is_first_step_output: Optional[bool] -
             When available, is_first_step_output indicates if the appended
             output token is the output of the first-step in multi-step.
             A value of None indicates that outputs from all steps in
@@ -2035,7 +2036,11 @@ def _build_logits_processors(
 
         logits_processors = []
 
-        if (guided_decoding := sampling_params.guided_decoding) is not None:
+        if sampling_params.guided_decoding is not None:
+            # Defensively copy sampling params since guided decoding logits
+            # processors can have different state for each request
+            sampling_params = copy.copy(sampling_params)
+            guided_decoding = sampling_params.guided_decoding
 
             logger.debug(
                 "Building guided decoding logits processor in "
@@ -2046,7 +2051,9 @@ def _build_logits_processors(
                 self.decoding_config.guided_decoding_backend
 
             processor = get_local_guided_decoding_logits_processor(
-                guided_params=guided_decoding, tokenizer=tokenizer)
+                guided_params=guided_decoding,
+                tokenizer=tokenizer,
+                model_config=self.model_config)
             if processor:
                 logits_processors.append(processor)
 

vllm/engine/multiprocessing/client.py

@@ -472,8 +472,8 @@ def generate(
             trace_headers: OpenTelemetry trace headers.
             prompt_adapter_request: Prompt Adapter request to use
                                             for generation, if any.
-            priority: Priority of the request (lower means earlier handling). 
-                Any priority other than 0 will lead to an error if the 
+            priority: Priority of the request (lower means earlier handling).
+                Any priority other than 0 will lead to an error if the
                 scheduling policy is not "priority".
         """
         if inputs is not None:
@@ -586,6 +586,7 @@ async def _process_request(
                     default_guided_backend=(self.decoding_config.guided_decoding_backend
                         if self.decoding_config
                         else DecodingConfig.guided_decoding_backend),
+                    model_config=self.model_config
                 )
 
         # 1) Create output queue for this requests.

vllm/model_executor/guided_decoding/__init__.py

@@ -1,14 +1,54 @@
-from typing import Optional
+from __future__ import annotations
 
-from vllm.logits_process import LogitsProcessor
-from vllm.sampling_params import GuidedDecodingParams
+from typing import TYPE_CHECKING
+
+from vllm.logger import init_logger
+
+if TYPE_CHECKING:
+    from transformers import PreTrainedTokenizer
+
+    from vllm.config import ModelConfig
+    from vllm.logits_process import LogitsProcessor
+    from vllm.sampling_params import GuidedDecodingParams
+
+logger = init_logger(__name__)
+
+
+def maybe_backend_fallback(
+        guided_params: GuidedDecodingParams) -> GuidedDecodingParams:
+    # lm-format-enforce doesn't support grammar, fallback to xgrammar
+    if (guided_params.backend == "lm-format-enforcer"
+            and guided_params.grammar is not None):
+        logger.warning(
+            "lm-format-enforcer does not support grammar guided decoding. "
+            "Falling back to use xgrammar instead.")
+        guided_params.backend = "xgrammar"
+
+    if guided_params.backend == "xgrammar":
+        # xgrammar doesn't support regex or choice, fallback to outlines
+        if guided_params.regex is not None or guided_params.choice is not None:
+            logger.warning(
+                "xgrammar only supports json or grammar guided decoding. "
+                "Falling back to use outlines instead.")
+            guided_params.backend = "outlines"
+
+        # xgrammar only supports EBNF grammars and uses the GBNF format
+        # https://github.com/ggerganov/llama.cpp/blob/master/grammars/README.md
+        elif (guided_params.grammar is not None
+              and "::=" not in guided_params.grammar):
+            logger.warning("xgrammar only supports EBNF grammars. "
+                           "Falling back to use outlines instead.")
+            guided_params.backend = "outlines"
+
+    return guided_params
 
 
 async def get_guided_decoding_logits_processor(
-        guided_params: GuidedDecodingParams,
-        tokenizer) -> Optional[LogitsProcessor]:
+        guided_params: GuidedDecodingParams, tokenizer: PreTrainedTokenizer,
+        model_config: ModelConfig) -> LogitsProcessor | None:
+    guided_params = maybe_backend_fallback(guided_params)
     # CFG grammar not supported by LMFE, so we use outlines instead
-    if guided_params.backend == 'outlines' or guided_params.grammar:
+    if guided_params.backend == 'outlines':
         # NOTE: lazy import outlines to avoid https://github.com/vllm-project/vllm/issues/4193
         from vllm.model_executor.guided_decoding.outlines_decoding import (  # noqa
             get_outlines_guided_decoding_logits_processor)
@@ -19,17 +59,23 @@ async def get_guided_decoding_logits_processor(
             get_local_lm_format_enforcer_guided_decoding_logits_processor)
         return get_local_lm_format_enforcer_guided_decoding_logits_processor(
             guided_params, tokenizer)
+    if guided_params.backend == 'xgrammar':
+        from vllm.model_executor.guided_decoding.xgrammar_decoding import (  # noqa
+            get_local_xgrammar_guided_decoding_logits_processor)
+        return get_local_xgrammar_guided_decoding_logits_processor(
+            guided_params, tokenizer, model_config)
 
     raise ValueError(
         f"Unknown guided decoding backend '{guided_params.backend}'. "
-        "Must be one of 'outlines, 'lm-format-enforcer'")
+        "Must be one of 'outlines, 'lm-format-enforcer', 'xgrammar'")
 
 
 def get_local_guided_decoding_logits_processor(
-        guided_params: GuidedDecodingParams,
-        tokenizer) -> Optional[LogitsProcessor]:
+        guided_params: GuidedDecodingParams, tokenizer: PreTrainedTokenizer,
+        model_config: ModelConfig) -> LogitsProcessor | None:
+    guided_params = maybe_backend_fallback(guided_params)
     # CFG grammar not supported by LMFE, so we use outlines instead
-    if guided_params.backend == 'outlines' or guided_params.grammar:
+    if guided_params.backend == 'outlines':
         # NOTE: lazy import outlines to avoid https://github.com/vllm-project/vllm/issues/4193
         from vllm.model_executor.guided_decoding.outlines_decoding import (  # noqa
             get_local_outlines_guided_decoding_logits_processor)
@@ -40,7 +86,12 @@ def get_local_guided_decoding_logits_processor(
             get_local_lm_format_enforcer_guided_decoding_logits_processor)
         return get_local_lm_format_enforcer_guided_decoding_logits_processor(
             guided_params, tokenizer)
+    if guided_params.backend == 'xgrammar':
+        from vllm.model_executor.guided_decoding.xgrammar_decoding import (  # noqa
+            get_local_xgrammar_guided_decoding_logits_processor)
+        return get_local_xgrammar_guided_decoding_logits_processor(
+            guided_params, tokenizer, model_config)
 
     raise ValueError(
         f"Unknown guided decoding backend '{guided_params.backend}'. "
-        "Must be one of 'outlines, 'lm-format-enforcer'")
+        "Must be one of 'outlines, 'lm-format-enforcer', 'xgrammar'")