utils.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
import msgspec
from abc import ABC
import torch

from vllm.sampling_params import SamplingParams

_SAMPLING_EPS = 1e-5


def is_spec_decode_unsupported(sampling_params: SamplingParams) -> bool:
    """True if request is incompatible with speculative decoding"""
    return (sampling_params.frequency_penalty != 0.0
            or sampling_params.presence_penalty != 0.0
            or sampling_params.repetition_penalty != 1.0
            or sampling_params.min_p > _SAMPLING_EPS
            or sampling_params.logprobs is not None)
    
class DraftProbs(ABC):  # type: ignore[call-arg]
    """Draft probs corresponding to in-progress sequences."""

    # spec tokens probs. 
    draft_probs: torch.Tensor

    # The request id list.
    _req_ids: list[str]

    def __init__(self, draft_probs, req_ids):
        assert len(req_ids) == len(draft_probs)
        self.draft_probs = draft_probs
        self._req_ids = req_ids

    def update(self,
               draft_probs: torch.Tensor,
               tmp_req_ids: list[str]):
        diff_req_ids = [item for item in self._req_ids if item not in tmp_req_ids]
        index = [self._req_ids.index(req_id) for req_id in diff_req_ids]
        self._req_ids = diff_req_ids
        self.draft_probs = self.draft_probs[index]
        self.draft_probs = torch.cat([self.draft_probs, draft_probs])
        
        self._req_ids.extend(tmp_req_ids)
        assert len(self._req_ids) == len(self.draft_probs)

    def prune(self, req_ids: list[str]):
        new_req_ids = [req_id for req_id in self._req_ids if req_id not in req_ids]
        if new_req_ids != self._req_ids:
            # Batch contents changed - prune removed sequences.
            index = [self._req_ids.index(req_id) for req_id in new_req_ids]
            self.draft_probs = self.draft_probs[index]
            self._req_ids = new_req_ids

    def get_probs(self, req_ids: list[str]):
        index = [self._req_ids.index(req_id) for req_id in req_ids]
        return self.draft_probs[index]