[Core][Performance] Add XGrammar support for guided decoding and set it as default (#10785)

Signed-off-by: Aaron Pham <contact@aarnphm.xyz>
Signed-off-by: mgoin <michael@neuralmagic.com>
Co-authored-by: mgoin <michael@neuralmagic.com>

docs/source/conf.py

@@ -178,6 +178,7 @@ autodoc_mock_imports = [
     "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

@@ -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},"

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 @@ class EngineArgs:
         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
@@ -507,7 +508,8 @@ class _AsyncLLMEngine(LLMEngine):
                 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,
@@ -528,22 +530,30 @@ class _AsyncLLMEngine(LLMEngine):
 
 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
@@ -2036,7 +2037,11 @@ class LLMEngine:
 
         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 "
@@ -2047,7 +2052,9 @@ class LLMEngine:
                 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

@@ -589,6 +589,7 @@ class MQLLMEngineClient(EngineClient):
                     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 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'")

vllm/model_executor/guided_decoding/xgrammar_decoding.py

@@ -0,0 +1,251 @@
+# noqa: UP007
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass, field
+from typing import TYPE_CHECKING, Any, NamedTuple
+
+import torch
+from transformers import PreTrainedTokenizerFast
+
+try:
+    import xgrammar as xgr
+    from xgrammar.base import _core as xgr_core
+except ImportError:
+    pass
+
+if TYPE_CHECKING:
+    from transformers import PreTrainedTokenizer
+
+    from vllm.config import ModelConfig
+    from vllm.sampling_params import GuidedDecodingParams
+
+
+# TODO: passing batch size to max threads here
+def get_local_xgrammar_guided_decoding_logits_processor(
+        guided_params: GuidedDecodingParams,
+        tokenizer: PreTrainedTokenizer,
+        model_config: ModelConfig,
+        max_threads: int = 8):
+    config = GrammarConfig.from_guided_params(guided_params=guided_params,
+                                              model_config=model_config,
+                                              tokenizer=tokenizer,
+                                              max_threads=max_threads)
+    return XGrammarLogitsProcessor(config)
+
+
+class TokenizerData(NamedTuple):
+    """Immutable container for cached tokenizer data."""
+    encoded_vocab: list[str]
+    stop_token_ids: list[int] | None
+    backend_str: str
+
+
+class TokenizerDataCache:
+    """Cache manager for tokenizer data to avoid repeated processing."""
+    _cache: dict[int, TokenizerData] = {}
+
+    @classmethod
+    def get_tokenizer_data(cls,
+                           tokenizer: PreTrainedTokenizer) -> TokenizerData:
+        tokenizer_hash = hash(tokenizer)
+
+        if tokenizer_hash not in cls._cache:
+            # Vendored from xgrammar logic since we cannot pickle the tokenizer
+            # https://github.com/mlc-ai/xgrammar/blob/d77c0a0173ef14779c918e3be7966ba852f7910f/python/xgrammar/tokenizer_info.py#L98 # noqa: E501
+            try:
+                encoded_vocab = [
+                    token for token, _ in sorted(tokenizer.get_vocab().items(),
+                                                 key=lambda x: x[1])
+                ]
+            except AttributeError as e:
+                raise ValueError(
+                    f"Cannot get the vocabulary of the tokenizer "
+                    f"{type(tokenizer)}. The tokenizer should have a "
+                    "get_vocab method.") from e
+
+            stop_token_ids = None
+            backend_str = xgr.VocabType.RAW
+            if isinstance(tokenizer, PreTrainedTokenizerFast):
+                backend_str = tokenizer.backend_tokenizer.to_str()
+                if stop_token_ids is None and hasattr(
+                        tokenizer,
+                        "eos_token_id") and tokenizer.eos_token_id is not None:
+                    stop_token_ids = [tokenizer.eos_token_id]
+
+            cls._cache[tokenizer_hash] = TokenizerData(
+                encoded_vocab=encoded_vocab,
+                stop_token_ids=stop_token_ids,
+                backend_str=backend_str)
+
+        return cls._cache[tokenizer_hash]
+
+
+class GrammarCompilerCache:
+    """
+    Cache for GrammarCompiler instances based on tokenizer.
+
+    This cache reduces the overhead of creating new compiler instances when
+    using the same tokenizer configuration.
+    """
+    _cache: dict[str, xgr.GrammarCompiler] = {}
+
+    @classmethod
+    def get_compiler(cls, config: GrammarConfig) -> xgr.GrammarCompiler:
+        cache_key = str(config.tokenizer_hash)
+
+        if cache_key not in cls._cache:
+            assert config.encoded_vocab is not None
+            tokenizer_info = xgr.TokenizerInfo._create_from_handle(
+                xgr_core.TokenizerInfo.from_huggingface(
+                    config.encoded_vocab, config.backend_str,
+                    config.vocab_size, config.stop_token_ids))
+            cls._cache[cache_key] = xgr.GrammarCompiler(
+                tokenizer_info, max_threads=config.max_threads)
+
+        return cls._cache[cache_key]
+
+
+@dataclass
+class GrammarConfig:
+    """Serializable configuration for grammar compilation"""
+    tokenizer_hash: int
+    vocab_size: int
+    json_str: str | None = None
+    grammar_str: str | None = None
+    json_object: bool | None = None
+    max_threads: int = 8
+    # Only populated if tokenizer_hash not in cache
+    encoded_vocab: list[str] | None = None
+    stop_token_ids: list[int] | None = None
+    backend_str: str | None = None
+
+    @classmethod
+    def from_guided_params(cls,
+                           guided_params: GuidedDecodingParams,
+                           model_config: ModelConfig,
+                           tokenizer: PreTrainedTokenizer,
+                           max_threads: int = 8) -> GrammarConfig:
+
+        tokenizer_hash = hash(tokenizer)
+        # Only get tokenizer data if not already cached
+        if tokenizer_hash in TokenizerDataCache._cache:
+            encoded_vocab = None
+            stop_token_ids = None
+            backend_str = None
+        else:
+            tokenizer_data = TokenizerDataCache.get_tokenizer_data(tokenizer)
+            encoded_vocab = tokenizer_data.encoded_vocab
+            stop_token_ids = tokenizer_data.stop_token_ids
+            backend_str = tokenizer_data.backend_str
+
+        if guided_params.json:
+            if not isinstance(guided_params.json, str):
+                json_str = json.dumps(guided_params.json)
+            else:
+                json_str = guided_params.json
+            return cls(json_str=json_str,
+                       vocab_size=model_config.hf_config.vocab_size,
+                       encoded_vocab=encoded_vocab,
+                       stop_token_ids=stop_token_ids,
+                       backend_str=backend_str,
+                       tokenizer_hash=tokenizer_hash,
+                       max_threads=max_threads)
+        elif guided_params.grammar:
+            return cls(grammar_str=guided_params.grammar,
+                       vocab_size=model_config.hf_config.vocab_size,
+                       encoded_vocab=encoded_vocab,
+                       stop_token_ids=stop_token_ids,
+                       backend_str=backend_str,
+                       tokenizer_hash=tokenizer_hash,
+                       max_threads=max_threads)
+        elif guided_params.json_object:
+            return cls(json_object=True,
+                       vocab_size=model_config.hf_config.vocab_size,
+                       encoded_vocab=encoded_vocab,
+                       stop_token_ids=stop_token_ids,
+                       backend_str=backend_str,
+                       tokenizer_hash=tokenizer_hash,
+                       max_threads=max_threads)
+        else:
+            raise ValueError(
+                "Currently only support JSON and EBNF grammar mode for xgrammar"
+            )
+
+
+@dataclass
+class XGrammarLogitsProcessor:
+    """Wrapper class to support pickle protocol"""
+    config: GrammarConfig
+
+    ctx: xgr.CompiledGrammar | None = None
+    token_bitmask: torch.Tensor = None  # type: ignore[assignment]
+    matchers: list[xgr.GrammarMatcher] = field(default_factory=list)
+    batch_size: int = field(default=1)
+    prefilled: bool = field(default=False)
+
+    def __getstate__(self) -> dict[str, Any]:
+        return {'config': self.config}
+
+    def __setstate__(self, state: dict[str, Any]):
+        self.config = state['config']
+
+        self.ctx = None
+        self.matchers = []
+        self.batch_size = 1
+        self.token_bitmask = None  # type: ignore[assignment]
+        self.prefilled = False
+
+    def _ensure_ctx(self):
+        """Lazily initialize the processor in the worker process"""
+        if self.ctx is None:
+            compiler = GrammarCompilerCache.get_compiler(self.config)
+            if self.config.json_str is not None:
+                self.ctx = compiler.compile_json_schema(self.config.json_str)
+            elif self.config.grammar_str is not None:
+                self.ctx = compiler.compile_grammar(self.config.grammar_str)
+            elif self.config.json_object:
+                self.ctx = compiler.compile_builtin_json_grammar()
+            else:
+                raise ValueError(
+                    "Invalid configuration for xgrammar logits processor")
+
+    def __call__(self, input_ids: list[int],
+                 scores: torch.Tensor) -> torch.Tensor:
+        if self.ctx is None:
+            self._ensure_ctx()
+
+        if len(self.matchers) == 0:
+            self.matchers = [
+                xgr.GrammarMatcher(self.ctx) for _ in range(self.batch_size)
+            ]
+            self.token_bitmask = xgr.allocate_token_bitmask(
+                self.batch_size, self.config.vocab_size)
+
+        if not self.prefilled:
+            # Have not sampled a token yet
+            self.prefilled = True
+        else:
+            for i, matcher in enumerate(self.matchers):
+                if not matcher.is_terminated():
+                    sampled_token = input_ids[-1]
+                    assert self.matchers[i].accept_token(sampled_token)
+
+        for i, matcher in enumerate(self.matchers):
+            if not matcher.is_terminated():
+                # @ubospica: ideally, fill_next_token_bitmask should be
+                # parallelized with model decoding
+                # See https://github.com/vllm-project/vllm/pull/10785/files#r1864278303
+                matcher.fill_next_token_bitmask(self.token_bitmask, i)
+
+        # token_bitmask is a CPU tensor for use with accept_token and
+        # fill_next_token_bitmask so we move it to the device of scores
+        device_type = scores.device.type
+        if device_type != "cuda":
+            scores = scores.to("cpu")
+        xgr.apply_token_bitmask_inplace(scores,
+                                        self.token_bitmask.to(scores.device))
+        if device_type != "cuda":
+            scores = scores.to(device_type)
+
+        return scores