fix: [vLLM multimodel] launch image loading in parallel (#5444)

Signed-off-by: Guan Luo <41310872+GuanLuo@users.noreply.github.com>

components/src/dynamo/vllm/handlers.py

@@ -757,6 +757,48 @@ class BaseWorkerHandler(ABC):
 
         return prompt, sequence_length, embeddings_tensor
 
+    async def _load_image_batch(
+        self, image_mm_items: list[Dict[str, Any]]
+    ) -> list[Any]:
+        """
+        Load a batch of images from multimodal data items.
+
+        Args:
+            image_mm_items: List of multimodal data items for images
+        Returns:
+            List of loaded image data
+        Raises:
+            Exception: If any image fails to load
+        """
+        image_futures = []
+        for item in image_mm_items:
+            if isinstance(item, dict) and URL_VARIANT_KEY in item:
+                url = item[URL_VARIANT_KEY]
+                image_futures.append(self.image_loader.load_image(url))
+                logger.debug(f"Preparing to load image from URL: {url[:80]}...")
+            elif isinstance(item, dict) and DECODED_VARIANT_KEY in item:
+                logger.warning(
+                    "Decoded multimodal data not yet supported in standard worker"
+                )
+
+        results = await asyncio.gather(*image_futures, return_exceptions=True)
+        loaded_images = []
+        collective_exceptions = ""
+        for i, result in enumerate(results):
+            if isinstance(result, Exception):
+                url = image_mm_items[i].get(URL_VARIANT_KEY, "unknown")
+                logger.error(f"Failed to load image from {url[:80]}...: {result}")
+                collective_exceptions += (
+                    f"Failed to load image from {url[:80]}...: {result}\n"
+                )
+                continue
+            loaded_images.append(result)
+
+        if collective_exceptions:
+            raise Exception(collective_exceptions)
+
+        return loaded_images
+
     async def _extract_multimodal_data(
         self, request: Dict[str, Any]
     ) -> Dict[str, Any] | None:
@@ -777,25 +819,7 @@ class BaseWorkerHandler(ABC):
         vllm_mm_data = {}
 
         # Process image_url entries
-        images = []
-        for item in mm_map.get(IMAGE_URL_KEY, []):
-            if isinstance(item, dict) and URL_VARIANT_KEY in item:
-                url = item[URL_VARIANT_KEY]
-                try:
-                    # ImageLoader supports both data: and http(s): URLs with caching
-                    image = await self.image_loader.load_image(url)
-                    images.append(image)
-                    logger.debug(f"Loaded image from URL: {url[:80]}...")
-                except Exception:
-                    logger.exception(f"Failed to load image from {url[:80]}...")
-                    raise
-            elif isinstance(item, dict) and DECODED_VARIANT_KEY in item:
-                # Decoded support from PRs #3971/#3988 (frontend decoding + NIXL transfer)
-                # Will contain NIXL metadata for direct memory access
-                # TODO: Implement NIXL read when PRs merge
-                logger.warning(
-                    "Decoded multimodal data not yet supported in standard worker"
-                )
+        images = await self._load_image_batch(mm_map.get(IMAGE_URL_KEY, []))
 
         if images:
             # vLLM expects single image or list