[Core] Asynchronous Output Processor (#7049)

Co-authored-by: Alexander Matveev <alexm@neuralmagic.com>

vllm/sequence.py

@@ -5,8 +5,8 @@ from abc import ABC, abstractmethod
 from array import array
 from collections import defaultdict
 from dataclasses import dataclass
-from typing import (TYPE_CHECKING, Any, Dict, List, Mapping, Optional, Set,
-                    Tuple, Union, cast)
+from typing import (TYPE_CHECKING, Any, Callable, Dict, List, Mapping,
+                    Optional, Set, Tuple, Union, cast)
 
 import msgspec
 import torch
@@ -474,11 +474,8 @@ class Sequence:
         """Reset the sequence states for recomputation."""
         self.data.reset_state_for_recompute()
 
-    def append_token_id(
-        self,
-        token_id: int,
-        logprobs: Dict[int, Logprob],
-    ) -> None:
+    def append_token_id(self, token_id: int, logprobs: Dict[int,
+                                                            Logprob]) -> None:
         assert token_id in logprobs
         self.output_logprobs.append(logprobs)
         self.data.append_token_id(token_id, logprobs[token_id].logprob)
@@ -1293,6 +1290,8 @@ class ExecuteModelRequest(
     finished_requests_ids: List[str] = msgspec.field(default_factory=list)
     # The last sampled token ids for multi step decoding.
     last_sampled_token_ids: Optional[torch.Tensor] = None
+    # Async postprocessor
+    output_proc_callback_fn: Optional[Callable] = None
 
     @property
     def is_first_multi_step(self) -> bool:
@@ -1338,4 +1337,5 @@ class ExecuteModelRequest(
             num_steps=self.num_steps,
             finished_requests_ids=self.finished_requests_ids,
             last_sampled_token_ids=self.last_sampled_token_ids.clone()
-            if self.last_sampled_token_ids is not None else None)
+            if self.last_sampled_token_ids is not None else None,
+            output_proc_callback_fn=self.output_proc_callback_fn)