LM Format Enforcer Guided Decoding Support (#3868)

Co-authored-by: Simon Mo <simon.mo@hey.com>

requirements-common.txt

@@ -11,6 +11,7 @@ uvicorn[standard]
 pydantic >= 2.0  # Required for OpenAI server.
 prometheus_client >= 0.18.0
 tiktoken == 0.6.0  # Required for DBRX tokenizer
+lm-format-enforcer == 0.9.3
 outlines == 0.0.34 # Requires torch >= 2.1.0
 typing_extensions
 filelock >= 3.10.4 # filelock starts to support `mode` argument from 3.10.4

tests/entrypoints/test_guided_processors.py

@@ -1,11 +1,14 @@
 # This unit test should be moved to a new
 # tests/test_guided_decoding directory.
-
+import pytest
 import torch
 from transformers import AutoTokenizer
 
-from vllm.model_executor.guided_logits_processors import (JSONLogitsProcessor,
+from vllm.entrypoints.openai.protocol import CompletionRequest
-                                                          RegexLogitsProcessor)
+from vllm.model_executor.guided_decoding import (
+    get_guided_decoding_logits_processor)
+from vllm.model_executor.guided_decoding.outlines_logits_processors import (
+    JSONLogitsProcessor, RegexLogitsProcessor)
 
 TEST_SCHEMA = {
     "type": "object",
@@ -73,3 +76,36 @@ def test_guided_logits_processors():
     json_LP(token_ids, tensor)
     assert tensor.shape == original_tensor.shape
     assert not torch.allclose(tensor, original_tensor)
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("backend", ["outlines", "lm-format-enforcer"])
+async def test_guided_logits_processor_black_box(backend: str):
+    tokenizer = AutoTokenizer.from_pretrained('HuggingFaceH4/zephyr-7b-beta')
+    token_ids = tokenizer.encode(
+        f"Give an example IPv4 address with this regex: {TEST_REGEX}")
+    regex_request = CompletionRequest(model='test',
+                                      prompt=token_ids,
+                                      guided_regex=TEST_REGEX)
+    regex_lp = await get_guided_decoding_logits_processor(
+        backend, regex_request, tokenizer)
+    assert regex_lp is not None
+    tensor = torch.rand(32000)
+    original_tensor = torch.clone(tensor)
+    tensor = regex_lp(token_ids, tensor)
+    assert tensor.shape == original_tensor.shape
+    assert not torch.allclose(tensor, original_tensor)
+
+    token_ids = tokenizer.encode(
+        f"Give an employee profile that fits this schema: {TEST_SCHEMA}")
+    json_request = CompletionRequest(model='test',
+                                     prompt=token_ids,
+                                     guided_json=TEST_SCHEMA)
+    json_lp = await get_guided_decoding_logits_processor(
+        backend, json_request, tokenizer)
+    assert json_lp is not None
+    tensor = torch.rand(32000)
+    original_tensor = torch.clone(tensor)
+    tensor = json_lp(token_ids, tensor)
+    assert tensor.shape == original_tensor.shape
+    assert not torch.allclose(tensor, original_tensor)

tests/entrypoints/test_openai_server.py

@@ -506,7 +506,10 @@ async def test_logits_bias(server, client: openai.AsyncOpenAI):
     assert first_response != completion.choices[0].text
 
 
-async def test_guided_json_completion(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_json_completion(server, client: openai.AsyncOpenAI,
+                                      guided_decoding_backend: str):
     completion = await client.completions.create(
         model=MODEL_NAME,
         prompt=f"Give an example JSON for an employee profile "
@@ -514,7 +517,8 @@ async def test_guided_json_completion(server, client: openai.AsyncOpenAI):
         n=3,
         temperature=1.0,
         max_tokens=500,
-        extra_body=dict(guided_json=TEST_SCHEMA))
+        extra_body=dict(guided_json=TEST_SCHEMA,
+                        guided_decoding_backend=guided_decoding_backend))
 
     assert completion.id is not None
     assert completion.choices is not None and len(completion.choices) == 3
@@ -524,7 +528,10 @@ async def test_guided_json_completion(server, client: openai.AsyncOpenAI):
         jsonschema.validate(instance=output_json, schema=TEST_SCHEMA)
 
 
-async def test_guided_json_chat(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_json_chat(server, client: openai.AsyncOpenAI,
+                                guided_decoding_backend: str):
     messages = [{
         "role": "system",
         "content": "you are a helpful assistant"
@@ -538,8 +545,9 @@ async def test_guided_json_chat(server, client: openai.AsyncOpenAI):
     chat_completion = await client.chat.completions.create(
         model=MODEL_NAME,
         messages=messages,
-        max_tokens=500,
+        max_tokens=1000,
-        extra_body=dict(guided_json=TEST_SCHEMA))
+        extra_body=dict(guided_json=TEST_SCHEMA,
+                        guided_decoding_backend=guided_decoding_backend))
     message = chat_completion.choices[0].message
     assert message.content is not None
     json1 = json.loads(message.content)
@@ -555,8 +563,9 @@ async def test_guided_json_chat(server, client: openai.AsyncOpenAI):
     chat_completion = await client.chat.completions.create(
         model=MODEL_NAME,
         messages=messages,
-        max_tokens=500,
+        max_tokens=1000,
-        extra_body=dict(guided_json=TEST_SCHEMA))
+        extra_body=dict(guided_json=TEST_SCHEMA,
+                        guided_decoding_backend=guided_decoding_backend))
     message = chat_completion.choices[0].message
     assert message.content is not None
     json2 = json.loads(message.content)
@@ -565,14 +574,18 @@ async def test_guided_json_chat(server, client: openai.AsyncOpenAI):
     assert json1["age"] != json2["age"]
 
 
-async def test_guided_regex_completion(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_regex_completion(server, client: openai.AsyncOpenAI,
+                                       guided_decoding_backend: str):
     completion = await client.completions.create(
         model=MODEL_NAME,
         prompt=f"Give an example IPv4 address with this regex: {TEST_REGEX}",
         n=3,
         temperature=1.0,
         max_tokens=20,
-        extra_body=dict(guided_regex=TEST_REGEX))
+        extra_body=dict(guided_regex=TEST_REGEX,
+                        guided_decoding_backend=guided_decoding_backend))
 
     assert completion.id is not None
     assert completion.choices is not None and len(completion.choices) == 3
@@ -581,7 +594,10 @@ async def test_guided_regex_completion(server, client: openai.AsyncOpenAI):
         assert re.fullmatch(TEST_REGEX, completion.choices[i].text) is not None
 
 
-async def test_guided_regex_chat(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_regex_chat(server, client: openai.AsyncOpenAI,
+                                 guided_decoding_backend: str):
     messages = [{
         "role": "system",
         "content": "you are a helpful assistant"
@@ -595,7 +611,8 @@ async def test_guided_regex_chat(server, client: openai.AsyncOpenAI):
         model=MODEL_NAME,
         messages=messages,
         max_tokens=20,
-        extra_body=dict(guided_regex=TEST_REGEX))
+        extra_body=dict(guided_regex=TEST_REGEX,
+                        guided_decoding_backend=guided_decoding_backend))
     ip1 = chat_completion.choices[0].message.content
     assert ip1 is not None
     assert re.fullmatch(TEST_REGEX, ip1) is not None
@@ -606,21 +623,26 @@ async def test_guided_regex_chat(server, client: openai.AsyncOpenAI):
         model=MODEL_NAME,
         messages=messages,
         max_tokens=20,
-        extra_body=dict(guided_regex=TEST_REGEX))
+        extra_body=dict(guided_regex=TEST_REGEX,
+                        guided_decoding_backend=guided_decoding_backend))
     ip2 = chat_completion.choices[0].message.content
     assert ip2 is not None
     assert re.fullmatch(TEST_REGEX, ip2) is not None
     assert ip1 != ip2
 
 
-async def test_guided_choice_completion(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_choice_completion(server, client: openai.AsyncOpenAI,
+                                        guided_decoding_backend: str):
     completion = await client.completions.create(
         model=MODEL_NAME,
         prompt="The best language for type-safe systems programming is ",
         n=2,
         temperature=1.0,
         max_tokens=10,
-        extra_body=dict(guided_choice=TEST_CHOICE))
+        extra_body=dict(guided_choice=TEST_CHOICE,
+                        guided_decoding_backend=guided_decoding_backend))
 
     assert completion.id is not None
     assert completion.choices is not None and len(completion.choices) == 2
@@ -628,7 +650,10 @@ async def test_guided_choice_completion(server, client: openai.AsyncOpenAI):
         assert completion.choices[i].text in TEST_CHOICE
 
 
-async def test_guided_choice_chat(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_choice_chat(server, client: openai.AsyncOpenAI,
+                                  guided_decoding_backend: str):
     messages = [{
         "role": "system",
         "content": "you are a helpful assistant"
@@ -642,7 +667,8 @@ async def test_guided_choice_chat(server, client: openai.AsyncOpenAI):
         model=MODEL_NAME,
         messages=messages,
         max_tokens=10,
-        extra_body=dict(guided_choice=TEST_CHOICE))
+        extra_body=dict(guided_choice=TEST_CHOICE,
+                        guided_decoding_backend=guided_decoding_backend))
     choice1 = chat_completion.choices[0].message.content
     assert choice1 in TEST_CHOICE
 
@@ -655,18 +681,23 @@ async def test_guided_choice_chat(server, client: openai.AsyncOpenAI):
         model=MODEL_NAME,
         messages=messages,
         max_tokens=10,
-        extra_body=dict(guided_choice=TEST_CHOICE))
+        extra_body=dict(guided_choice=TEST_CHOICE,
+                        guided_decoding_backend=guided_decoding_backend))
     choice2 = chat_completion.choices[0].message.content
     assert choice2 in TEST_CHOICE
     assert choice1 != choice2
 
 
-async def test_guided_decoding_type_error(server, client: openai.AsyncOpenAI):
+@pytest.mark.parametrize("guided_decoding_backend",
+                         ["outlines", "lm-format-enforcer"])
+async def test_guided_decoding_type_error(server, client: openai.AsyncOpenAI,
+                                          guided_decoding_backend: str):
     with pytest.raises(openai.BadRequestError):
         _ = await client.completions.create(
             model=MODEL_NAME,
             prompt="Give an example JSON that fits this schema: 42",
-            extra_body=dict(guided_json=42))
+            extra_body=dict(guided_json=42,
+                            guided_decoding_backend=guided_decoding_backend))
 
     messages = [{
         "role": "system",

vllm/config.py

@@ -1079,6 +1079,21 @@ def _get_and_verify_max_len(
     return int(max_model_len)
 
 
+@dataclass
+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'
+
+    def __post_init__(self):
+        valid_guided_backends = ['outlines', 'lm-format-enforcer']
+        backend = self.guided_decoding_backend
+        if backend not in valid_guided_backends:
+            raise ValueError(f"Invalid guided_decoding_backend '{backend},"
+                             f"must be one of {valid_guided_backends}")
+
+
 @dataclass(frozen=True)
 class EngineConfig:
     """Dataclass which contains all engine-related configuration. This
@@ -1093,6 +1108,7 @@ class EngineConfig:
     lora_config: Optional[LoRAConfig]
     vision_language_config: Optional[VisionLanguageConfig]
     speculative_config: Optional[SpeculativeConfig]
+    decoding_config: Optional[DecodingConfig]
     tensorizer_config: Optional[TensorizerConfig]
 
     def __post_init__(self):

vllm/engine/arg_utils.py

@@ -5,9 +5,9 @@ import os
 from dataclasses import dataclass
 from typing import BinaryIO, Optional, Union
 
-from vllm.config import (CacheConfig, DeviceConfig, EngineConfig, LoRAConfig,
+from vllm.config import (CacheConfig, DecodingConfig, DeviceConfig,
-                         ModelConfig, ParallelConfig, SchedulerConfig,
+                         EngineConfig, LoRAConfig, ModelConfig, ParallelConfig,
-                         SpeculativeConfig, TensorizerConfig,
+                         SchedulerConfig, SpeculativeConfig, TensorizerConfig,
                          TokenizerPoolConfig, VisionLanguageConfig)
 from vllm.model_executor.tensorizer_loader import TensorizerArgs
 from vllm.utils import str_to_int_tuple
@@ -80,6 +80,7 @@ class EngineArgs:
     scheduler_delay_factor: float = 0.0
     enable_chunked_prefill: bool = False
 
+    guided_decoding_backend: str = 'outlines'
     # Speculative decoding configuration.
     speculative_model: Optional[str] = None
     num_speculative_tokens: Optional[int] = None
@@ -200,6 +201,13 @@ class EngineArgs:
                             default=EngineArgs.max_model_len,
                             help='model context length. If unspecified, '
                             'will be automatically derived from the model.')
+        parser.add_argument(
+            '--guided-decoding-backend',
+            type=str,
+            default='outlines',
+            choices=['outlines', 'lm-format-enforcer'],
+            help='Which engine will be used for guided decoding'
+            ' (JSON schema / regex etc)')
         # Parallel arguments
         parser.add_argument('--worker-use-ray',
                             action='store_true',
@@ -511,6 +519,9 @@ class EngineArgs:
         else:
             vision_language_config = None
 
+        decoding_config = DecodingConfig(
+            guided_decoding_backend=self.guided_decoding_backend)
+
         return EngineConfig(model_config=model_config,
                             cache_config=cache_config,
                             parallel_config=parallel_config,
@@ -519,6 +530,7 @@ class EngineArgs:
                             lora_config=lora_config,
                             vision_language_config=vision_language_config,
                             speculative_config=speculative_config,
+                            decoding_config=decoding_config,
                             tensorizer_config=tensorizer_config)
 
 

vllm/engine/llm_engine.py

@@ -4,9 +4,10 @@ from typing import Iterable, List, Optional, Tuple, Type, Union
 from transformers import PreTrainedTokenizer
 
 import vllm
-from vllm.config import (CacheConfig, DeviceConfig, LoRAConfig, ModelConfig,
+from vllm.config import (CacheConfig, DecodingConfig, DeviceConfig, LoRAConfig,
-                         ParallelConfig, SchedulerConfig, SpeculativeConfig,
+                         ModelConfig, ParallelConfig, SchedulerConfig,
-                         TensorizerConfig, VisionLanguageConfig)
+                         SpeculativeConfig, TensorizerConfig,
+                         VisionLanguageConfig)
 from vllm.core.scheduler import Scheduler, SchedulerOutputs
 from vllm.engine.arg_utils import EngineArgs
 from vllm.engine.metrics import StatLogger, Stats
@@ -74,6 +75,7 @@ class LLMEngine:
         lora_config: Optional[LoRAConfig],
         vision_language_config: Optional[VisionLanguageConfig],
         speculative_config: Optional[SpeculativeConfig],
+        decoding_config: Optional[DecodingConfig],
         tensorizer_config: Optional[TensorizerConfig],
         executor_class: Type[ExecutorBase],
         log_stats: bool,
@@ -100,6 +102,7 @@ class LLMEngine:
             f"kv_cache_dtype={cache_config.cache_dtype}, "
             f"quantization_param_path={model_config.quantization_param_path}, "
             f"device_config={device_config.device}, "
+            f"decoding_config={decoding_config!r}, "
             f"seed={model_config.seed})")
         # TODO(woosuk): Print more configs in debug mode.
 
@@ -111,6 +114,7 @@ class LLMEngine:
         self.scheduler_config = scheduler_config
         self.device_config = device_config
         self.speculative_config = speculative_config
+        self.decoding_config = decoding_config or DecodingConfig()
         self.tensorizer_config = tensorizer_config
         self.log_stats = log_stats
 

vllm/entrypoints/openai/protocol.py

@@ -133,6 +133,12 @@ class ChatCompletionRequest(BaseModel):
         description=(
             "If specified, the output will follow the context free grammar."),
     )
+    guided_decoding_backend: Optional[str] = Field(
+        default=None,
+        description=(
+            "If specified, will override the default guided decoding backend "
+            "of the server for this specific request. If set, must be either "
+            "'outlines' / 'lm-format-enforcer'"))
 
     # doc: end-chat-completion-extra-params
 
@@ -265,6 +271,12 @@ class CompletionRequest(BaseModel):
         description=(
             "If specified, the output will follow the context free grammar."),
     )
+    guided_decoding_backend: Optional[str] = Field(
+        default=None,
+        description=(
+            "If specified, will override the default guided decoding backend "
+            "of the server for this specific request. If set, must be one of "
+            "'outlines' / 'lm-format-enforcer'"))
 
     # doc: end-completion-extra-params
 

vllm/entrypoints/openai/serving_chat.py

@@ -68,9 +68,13 @@ class OpenAIServingChat(OpenAIServing):
                 request, prompt=prompt)
             sampling_params = request.to_sampling_params()
             lora_request = self._maybe_get_lora(request)
+            decoding_config = self.engine.engine.decoding_config
+            guided_decoding_backend = request.guided_decoding_backend \
+                or decoding_config.guided_decoding_backend
             guided_decode_logits_processor = (
                 await get_guided_decoding_logits_processor(
-                    request, await self.engine.get_tokenizer()))
+                    guided_decoding_backend, request, await
+                    self.engine.get_tokenizer()))
             if guided_decode_logits_processor:
                 if sampling_params.logits_processors is None:
                     sampling_params.logits_processors = []

vllm/entrypoints/openai/serving_completion.py

@@ -88,9 +88,13 @@ class OpenAIServingCompletion(OpenAIServing):
         try:
             sampling_params = request.to_sampling_params()
             lora_request = self._maybe_get_lora(request)
+            decoding_config = self.engine.engine.decoding_config
+            guided_decoding_backend = request.guided_decoding_backend \
+                or decoding_config.guided_decoding_backend
             guided_decode_logit_processor = (
                 await get_guided_decoding_logits_processor(
-                    request, await self.engine.get_tokenizer()))
+                    guided_decoding_backend, request, await
+                    self.engine.get_tokenizer()))
             if guided_decode_logit_processor is not None:
                 if sampling_params.logits_processors is None:
                     sampling_params.logits_processors = []

vllm/model_executor/guided_decoding/__init__.py

@@ -0,0 +1,25 @@
+from typing import Optional, Union
+
+from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
+                                              CompletionRequest)
+from vllm.model_executor.guided_decoding.lm_format_enforcer_decoding import (
+    get_lm_format_enforcer_guided_decoding_logits_processor)
+from vllm.model_executor.guided_decoding.outlines_decoding import (
+    get_outlines_guided_decoding_logits_processor)
+from vllm.sampling_params import LogitsProcessor
+
+
+async def get_guided_decoding_logits_processor(
+        guided_decoding_backend: str, request: Union[CompletionRequest,
+                                                     ChatCompletionRequest],
+        tokenizer) -> Optional[LogitsProcessor]:
+    if guided_decoding_backend == 'outlines':
+        return await get_outlines_guided_decoding_logits_processor(
+            request, tokenizer)
+    if guided_decoding_backend == 'lm-format-enforcer':
+        return await get_lm_format_enforcer_guided_decoding_logits_processor(
+            request, tokenizer)
+
+    raise ValueError(
+        f"Unknown guided decoding backend '{guided_decoding_backend}'. "
+        "Must be one of 'outlines, 'lm-format-enforcer'")

vllm/model_executor/guided_decoding/lm_format_enforcer_decoding.py

@@ -0,0 +1,69 @@
+from functools import lru_cache
+from json import loads as json_loads
+from typing import Optional, Union
+
+from lmformatenforcer import (CharacterLevelParser, JsonSchemaParser,
+                              RegexParser, StringParser,
+                              TokenEnforcerTokenizerData, UnionParser)
+from lmformatenforcer.integrations.vllm import (
+    build_vllm_logits_processor, build_vllm_token_enforcer_tokenizer_data)
+from pydantic import BaseModel
+from transformers import PreTrainedTokenizerBase
+
+from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
+                                              CompletionRequest)
+from vllm.model_executor.guided_decoding.outlines_decoding import (
+    get_outlines_guided_decoding_logits_processor)
+from vllm.sampling_params import LogitsProcessor
+
+
+async def get_lm_format_enforcer_guided_decoding_logits_processor(
+        request: Union[CompletionRequest, ChatCompletionRequest],
+        tokenizer) -> Optional[LogitsProcessor]:
+    """
+    Given an OpenAI-compatible request, check for guided decoding parameters
+    and get the necessary logits processor for the given guide.
+    We cache logit processors by (guide, tokenizer), and on cache hit
+    we make a shallow copy to reuse the same underlying FSM.
+    """
+
+    tokenizer_data = _cached_build_vllm_token_enforcer_tokenizer_data(
+        tokenizer)
+    character_level_parser: CharacterLevelParser
+    if request.guided_json:
+        schema = _normalize_json_schema_object(request.guided_json)
+        character_level_parser = JsonSchemaParser(schema)
+    elif request.guided_choice:
+        character_level_parser = UnionParser(
+            [StringParser(choice) for choice in request.guided_choice])
+    elif request.guided_regex:
+        character_level_parser = RegexParser(request.guided_regex)
+    elif request.guided_grammar:
+        # CFG grammar not supported by LMFE, revert to outlines
+        return await get_outlines_guided_decoding_logits_processor(
+            request, tokenizer)
+    elif (request.response_format is not None
+          and request.response_format.type == "json_object"):
+        character_level_parser = JsonSchemaParser(
+            None)  # None means any json object
+    else:
+        return None
+
+    logits_processor = build_vllm_logits_processor(tokenizer_data,
+                                                   character_level_parser)
+    return logits_processor
+
+
+def _normalize_json_schema_object(schema: Union[str, dict, BaseModel]) -> dict:
+    if isinstance(schema, str):
+        return json_loads(schema)
+    if isinstance(schema, dict):
+        return schema
+    if isinstance(schema, BaseModel):
+        return schema.model_json_schema()
+
+
+@lru_cache
+def _cached_build_vllm_token_enforcer_tokenizer_data(
+        tokenizer: PreTrainedTokenizerBase) -> TokenEnforcerTokenizerData:
+    return build_vllm_token_enforcer_tokenizer_data(tokenizer)

vllm/model_executor/guided_decoding/outlines_decoding.py

@@ -12,9 +12,8 @@ from transformers import PreTrainedTokenizerBase
 
 from vllm.entrypoints.openai.protocol import (ChatCompletionRequest,
                                               CompletionRequest)
-from vllm.model_executor.guided_logits_processors import (CFGLogitsProcessor,
+from vllm.model_executor.guided_decoding.outlines_logits_processors import (
-                                                          JSONLogitsProcessor,
+    CFGLogitsProcessor, JSONLogitsProcessor, RegexLogitsProcessor)
-                                                          RegexLogitsProcessor)
 
 
 class GuidedDecodingMode(Enum):
@@ -54,7 +53,7 @@ pair   : UNESCAPED_STRING ":" value
 global_thread_pool = None  # used for generating logits processor fsm
 
 
-async def get_guided_decoding_logits_processor(
+async def get_outlines_guided_decoding_logits_processor(
         request: Union[CompletionRequest, ChatCompletionRequest],
         tokenizer) -> Union[JSONLogitsProcessor, RegexLogitsProcessor]:
     """

vllm/model_executor/guided_decoding/outlines_logits_processors.py

@@ -13,9 +13,11 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import copy
 import json
 import math
 from collections import defaultdict
+from functools import lru_cache
 from typing import Callable, DefaultDict, Dict, List, Optional, Union
 
 import torch
@@ -27,50 +29,6 @@ from transformers import PreTrainedTokenizerBase
 
 class BaseLogitsProcessor:
 
-    def adapt_tokenizer(self, tokenizer: PreTrainedTokenizerBase):
-        """Adapt vLLM's tokenizer to use to compile the FSM.
-
-        The API of Outlines tokenizers is slightly different to that of
-        `transformers`. The decoder of outlines, returns a list whereas
-        the decode of vLLM returns an str. To sync the vLLM decoder with
-        outlines internal api, the decoder should be adapted. In addition
-        we need to handle the missing spaces to Llama's tokenizer to be
-        able to compile FSMs for this model.
-
-        """
-        if getattr(tokenizer, "_outlines_adapted", False):
-            return tokenizer
-
-        tokenizer.vocabulary = tokenizer.get_vocab()
-        tokenizer.special_tokens = set(tokenizer.all_special_tokens)
-
-        def convert_token_to_string(token: str) -> str:
-            from transformers.file_utils import SPIECE_UNDERLINE
-
-            string = tokenizer.convert_tokens_to_string([token])
-
-            # A hack to handle missing spaces to HF's Llama tokenizers
-            if token.startswith(SPIECE_UNDERLINE) or token == "<0x20>":
-                return " " + string
-
-            return string
-
-        def change_decoder(
-            decoder: Callable[[List[int]], str]
-        ) -> Callable[[List[int]], List[str]]:
-            """Sync vLLM's decoder with the outlines by returning list."""
-
-            def new_decoder(inp_tokens: List[int]) -> List[str]:
-                return [decoder(inp_tokens)]
-
-            return new_decoder
-
-        tokenizer.convert_token_to_string = convert_token_to_string
-        tokenizer.decode = change_decoder(tokenizer.decode)
-        setattr(tokenizer, "_outlines_adapted", True)  # noqa: B010
-
-        return tokenizer
-
     def init_state(self):
         """Initialize the FSM states."""
         self.fsm_state: DefaultDict[int, int] = defaultdict(int)
@@ -78,7 +36,6 @@ class BaseLogitsProcessor:
     def __call__(self, input_ids: List[int],
                  scores: torch.Tensor) -> torch.Tensor:
         """Use the FSM to bias the logits before sampling the next token."""
-
         seq_id = hash(tuple(input_ids))
 
         if len(input_ids) == 0:
@@ -96,7 +53,6 @@ class BaseLogitsProcessor:
                           device=scores.device)
         mask[allowed_tokens] = 0
         scores.add_(mask)
-
         return scores
 
 
@@ -113,7 +69,7 @@ class RegexLogitsProcessor(BaseLogitsProcessor):
             The model's tokenizer
 
         """
-        tokenizer = self.adapt_tokenizer(tokenizer)
+        tokenizer = _adapt_tokenizer(tokenizer)
         fsm = RegexFSM(regex_string, tokenizer)
         self.fsm = fsm
 
@@ -167,6 +123,54 @@ class CFGLogitsProcessor(BaseLogitsProcessor):
             The model's tokenizer
 
         """
-        tokenizer = self.adapt_tokenizer(tokenizer)
+        tokenizer = _adapt_tokenizer(tokenizer)
         fsm = CFGFSM(cfg, tokenizer)
         self.fsm = fsm
+
+
+@lru_cache
+def _adapt_tokenizer(tokenizer: PreTrainedTokenizerBase):
+    """Adapt vLLM's tokenizer to use to compile the FSM.
+
+    The API of Outlines tokenizers is slightly different to that of
+    `transformers`. The decoder of outlines, returns a list whereas
+    the decode of vLLM returns an str. To sync the vLLM decoder with
+    outlines internal api, the decoder should be adapted. In addition
+    we need to handle the missing spaces to Llama's tokenizer to be
+    able to compile FSMs for this model.
+
+    """
+    if getattr(tokenizer, "_outlines_adapted", False):
+        return tokenizer
+
+    tokenizer = copy.deepcopy(tokenizer)
+
+    tokenizer.vocabulary = tokenizer.get_vocab()
+    tokenizer.special_tokens = set(tokenizer.all_special_tokens)
+
+    def convert_token_to_string(token: str) -> str:
+        from transformers.file_utils import SPIECE_UNDERLINE
+
+        string = tokenizer.convert_tokens_to_string([token])
+
+        # A hack to handle missing spaces to HF's Llama tokenizers
+        if token.startswith(SPIECE_UNDERLINE) or token == "<0x20>":
+            return " " + string
+
+        return string
+
+    def change_decoder(
+        decoder: Callable[[List[int]],
+                          str]) -> Callable[[List[int]], List[str]]:
+        """Sync vLLM's decoder with the outlines by returning list."""
+
+        def new_decoder(inp_tokens: List[int]) -> List[str]:
+            return [decoder(inp_tokens)]
+
+        return new_decoder
+
+    tokenizer.convert_token_to_string = convert_token_to_string
+    tokenizer.decode = change_decoder(tokenizer.decode)
+    setattr(tokenizer, "_outlines_adapted", True)  # noqa: B010
+
+    return tokenizer