Introduce future indices (#11301)

python/sglang/srt/managers/overlap_utils.py

+from dataclasses import dataclass
+from typing import Optional
+
 import torch
 
 from sglang.srt.managers.schedule_batch import ModelWorkerBatch
@@ -13,6 +16,12 @@ def _resolve_future_token_ids(input_ids, future_token_ids_map):
     )
 
 
+@dataclass
+class FutureIndices:
+    indices: torch.Tensor
+    interval: Optional[slice] = None
+
+
 class FutureMap:
     def __init__(
         self,
@@ -30,23 +39,17 @@ class FutureMap:
             (self.future_buffer_len,), dtype=torch.int64, device=self.device
         )
 
-    def update_ct(self, bs: int) -> int:
-        """Update the circular buffer pointer and return the current pointer."""
+    def alloc_future_indices(self, bs: int) -> FutureIndices:
+        """Update the circular buffer pointer and allocate future indices."""
         cur_future_ct = self.future_ct
         self.future_ct = (cur_future_ct + bs) % self.future_limit
-        return cur_future_ct
+        start = cur_future_ct + 1
+        end = cur_future_ct + 1 + bs
+        indices = torch.arange(start, end, dtype=torch.int64, device=self.device)
+        return FutureIndices(indices=indices, interval=slice(start, end))
 
     def resolve_future(self, model_worker_batch: ModelWorkerBatch):
         _resolve_future_token_ids(model_worker_batch.input_ids, self.token_ids_buf)
 
-    def update_next_future(self, future_ct: int, bs: int):
-        return torch.arange(
-            -(future_ct + 1),
-            -(future_ct + 1 + bs),
-            -1,
-            dtype=torch.int64,
-            device=self.device,
-        )
-
-    def store_to_map(self, future_ct: int, bs: int, next_token_ids: torch.Tensor):
-        self.token_ids_buf[future_ct + 1 : future_ct + bs + 1] = next_token_ids
+    def store_to_map(self, future_indices: FutureIndices, next_token_ids: torch.Tensor):
+        self.token_ids_buf[future_indices.interval] = next_token_ids

python/sglang/srt/managers/scheduler.py

@@ -114,7 +114,7 @@ from sglang.srt.managers.io_struct import (
     UpdateWeightsFromTensorReqInput,
 )
 from sglang.srt.managers.mm_utils import init_embedding_cache
-from sglang.srt.managers.overlap_utils import FutureMap
+from sglang.srt.managers.overlap_utils import FutureIndices, FutureMap
 from sglang.srt.managers.schedule_batch import (
     FINISH_ABORT,
     ModelWorkerBatch,
@@ -217,7 +217,7 @@ class GenerationBatchResult:
     copy_done: Optional[torch.cuda.Event] = None
     delay_sample_launch: bool = False
     forward_batch: Optional[ForwardBatch] = None
-    future_map_ct: Optional[int] = None
+    future_indices: Optional[FutureIndices] = None
 
     def copy_to_cpu(self, return_logprob: bool = False):
         """Copy tensors to CPU in overlap scheduling.
@@ -2092,7 +2092,7 @@ class Scheduler(
                 )
 
                 bs = len(model_worker_batch.seq_lens)
-                cur_future_map_ct = self.future_map.update_ct(bs)
+                future_indices = self.future_map.alloc_future_indices(bs)
 
                 with self.forward_stream_ctx:
                     self.forward_stream.wait_stream(self.default_stream)
@@ -2108,22 +2108,19 @@ class Scheduler(
                     ).Event()
                     if not model_worker_batch.delay_sample_launch:
                         self.future_map.store_to_map(
-                            cur_future_map_ct, bs, batch_result.next_token_ids
+                            future_indices, batch_result.next_token_ids
                         )
                         batch_result.copy_to_cpu()
                     else:
-                        batch_result.future_map_ct = cur_future_map_ct
+                        batch_result.future_indices = future_indices
 
                 # FIXME(lsyin): move this assignment elsewhere
-                maybe_future_next_token_ids = self.future_map.update_next_future(
-                    cur_future_map_ct, bs
-                )
+                maybe_future_next_token_ids = -future_indices.indices
             else:
                 batch_result = self.model_worker.forward_batch_generation(
                     batch_or_worker_batch
                 )
                 maybe_future_next_token_ids = batch_result.next_token_ids
-                copy_done = None
 
             if not self.spec_algorithm.is_none():
                 # TODO(lsyin): unify this metric-updating logic with non-spec, and move it to decode processing
@@ -2182,8 +2179,8 @@ class Scheduler(
                 tmp_result.logits_output,
                 tmp_result.forward_batch,
             )
-            ct, bs = tmp_result.future_map_ct, len(tmp_batch.reqs)
-            self.future_map.store_to_map(ct, bs, tmp_result.next_token_ids)
+            future_indices = tmp_result.future_indices
+            self.future_map.store_to_map(future_indices, tmp_result.next_token_ids)
             tmp_result.copy_to_cpu()
             self.result_queue.appendleft((tmp_batch, tmp_result))