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[V1] Delay all xgrammar usage until needed #14616

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merged 1 commit into from
Mar 11, 2025
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[V1] Delay all xgrammar usage until needed #14616

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33 changes: 20 additions & 13 deletions vllm/v1/structured_output/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@
if TYPE_CHECKING:
import numpy as np
import numpy.typing as npt
import torch
import xgrammar as xgr

from vllm.v1.request import Request
Expand All @@ -27,14 +26,18 @@
class StructuredOutputManager:

def __init__(self, vllm_config: VllmConfig):
tokenizer_group = init_tokenizer_from_configs(
model_config=vllm_config.model_config,
scheduler_config=vllm_config.scheduler_config,
parallel_config=vllm_config.parallel_config,
lora_config=vllm_config.lora_config) # type: ignore[arg-type]
tokenizer_group.ping()
self.vocab_size = vllm_config.model_config.get_vocab_size()
self.vllm_config = vllm_config
self.init_complete = False

def _delayed_init(self):
"""Initialization delayed until we know it is needed."""
tokenizer_group = init_tokenizer_from_configs(
model_config=self.vllm_config.model_config,
scheduler_config=self.vllm_config.scheduler_config,
parallel_config=self.vllm_config.parallel_config,
lora_config=self.vllm_config.lora_config) # type: ignore[arg-type]
tokenizer_group.ping()

tokenizer = tokenizer_group.get_lora_tokenizer(None)
tokenizer_info = xgr.TokenizerInfo.from_huggingface(
Expand All @@ -47,12 +50,21 @@ def __init__(self, vllm_config: VllmConfig):
# compilation, so we set it to half the number of CPUs.
max_workers = max(1, (multiprocessing.cpu_count() + 1) // 2)
self.executor = ThreadPoolExecutor(max_workers=max_workers)
self._grammar_bitmask: Optional[torch.Tensor] = None
self._grammar_bitmask = xgr.allocate_token_bitmask(
self.vllm_config.scheduler_config.max_num_seqs, self.vocab_size)

self.init_complete = True

def grammar_init(self, request: Request) -> None:
if request.structured_output_request is None:
return

# The first time this is called, we need to finish initialization
# of xgrammar. We defer it to avoid the import of xgrammar and
# initialization cost if it is not going to be used.
if not self.init_complete:
self._delayed_init()

grammar: Future[Grammar] = self.executor.submit(
self._async_create_grammar, request)
request.structured_output_request.grammar = grammar # type: ignore[assignment]
Expand Down Expand Up @@ -100,11 +112,6 @@ def grammar_bitmask(
if not structured_output_request_ids:
return None

if self._grammar_bitmask is None:
self._grammar_bitmask = xgr.allocate_token_bitmask(
self.vllm_config.scheduler_config.max_num_seqs,
self.vocab_size)

# Fill the bitmask using the index of each request equal to its
# position in the batch. Resize the bitmask down to the size of
# the batch.
Expand Down