Add update_weights_from_disk endpoint to Engine (#4102)

Co-authored-by: zhaochenyang20 <zhaochen20@outlook.com>

python/sglang/srt/entrypoints/engine.py

@@ -44,6 +44,7 @@ from sglang.srt.managers.io_struct import (
     InitWeightsUpdateGroupReqInput,
     ReleaseMemoryOccupationReqInput,
     ResumeMemoryOccupationReqInput,
+    UpdateWeightFromDiskReqInput,
     UpdateWeightsFromDistributedReqInput,
     UpdateWeightsFromTensorReqInput,
 )
@@ -302,6 +303,27 @@ class Engine:
             self.tokenizer_manager.update_weights_from_tensor(obj, None)
         )
 
+    def update_weights_from_disk(
+        self,
+        model_path: str,
+        load_format: Optional[str] = None,
+    ):
+        """Update the weights from disk inplace without re-launching the engine.
+
+        This method allows updating the model weights from disk without restarting
+        the engine. It can be used to load a different model or update weights with
+        new training.
+        """
+        obj = UpdateWeightFromDiskReqInput(
+            model_path=model_path,
+            load_format=load_format,
+        )
+
+        loop = asyncio.get_event_loop()
+        return loop.run_until_complete(
+            self.tokenizer_manager.update_weights_from_disk(obj, None)
+        )
+
     def get_weights_by_name(self, name: str, truncate_size: int = 100):
         """Get weights by parameter name."""
         obj = GetWeightsByNameReqInput(name=name, truncate_size=truncate_size)