[feat] Reduce GPU memory overhead by using weakref (#9673)

python/sglang/srt/sampling/penaltylib/orchestrator.py

 from __future__ import annotations
 
 import abc
-from typing import TYPE_CHECKING, Set, Type
+import weakref
+from typing import TYPE_CHECKING, Optional, Set, Type
 
 import torch
 
@@ -17,7 +18,7 @@ class BatchedPenalizerOrchestrator:
         penalizers: Set[Type["_BatchedPenalizer"]],
     ):
         self.vocab_size = vocab_size
-        self.batch = batch
+        self._batch_ref = weakref.ref(batch)
         self.device = batch.device
         self.penalizers = {Penalizer: Penalizer(self) for Penalizer in penalizers}
 
@@ -27,6 +28,17 @@ class BatchedPenalizerOrchestrator:
             is_required |= pen_is_required
         self.is_required = is_required
 
+    @property
+    def batch(self) -> ScheduleBatch | None:
+        return self._batch_ref()
+
+    @batch.setter
+    def batch(self, value: Optional[ScheduleBatch]):
+        if value is None:
+            self._batch_ref = lambda: None
+        else:
+            self._batch_ref = weakref.ref(value)
+
     def reqs(self):
         return self.batch.reqs