[4/N]DP refactor: support watching mode get_load and shortest queue strategy (#10201)

python/sglang/utils.py

@@ -472,6 +472,10 @@ def wait_for_server(base_url: str, timeout: int = None) -> None:
 class TypeBasedDispatcher:
     def __init__(self, mapping: List[Tuple[Type, Callable]]):
         self._mapping = mapping
+        self._fallback_fn = None
+
+    def add_fallback_fn(self, fallback_fn: Callable):
+        self._fallback_fn = fallback_fn
 
     def __iadd__(self, other: "TypeBasedDispatcher"):
         self._mapping.extend(other._mapping)
@@ -481,6 +485,9 @@ class TypeBasedDispatcher:
         for ty, fn in self._mapping:
             if isinstance(obj, ty):
                 return fn(obj)
+
+        if self._fallback_fn is not None:
+            return self._fallback_fn(obj)
         raise ValueError(f"Invalid object: {obj}")