FIX: Offload local dataset file reads (#2402)

Co-authored-by: hannahwestra25 <hannahwestra@microsoft.com>

Author: biefan

pyrit/datasets/seed_datasets/local/local_dataset_loader.py

@@ -1,6 +1,7 @@
 # Copyright (c) Microsoft Corporation.
 # Licensed under the MIT license.
 
+import asyncio
 import logging
 from collections.abc import Callable
 from dataclasses import fields
@@ -68,7 +69,7 @@ async def fetch_dataset_async(self, *, cache: bool = True) -> SeedDataset:
         """
         try:
             logger.info(f"Loading local dataset from {self.file_path}")
-            dataset = SeedDataset.from_yaml_file(self.file_path)
+            dataset = await asyncio.to_thread(SeedDataset.from_yaml_file, self.file_path)
             if not dataset.dataset_name:
                 dataset.dataset_name = self.dataset_name
             return dataset
@@ -91,8 +92,7 @@ async def _parse_metadata_async(self) -> SeedDatasetMetadata | None:
         """
         valid_fields = [f.name for f in fields(SeedDatasetMetadata)]
         try:
-            with open(self.file_path, encoding="utf-8") as f:
-                dataset = yaml.safe_load(f)
+            dataset = await asyncio.to_thread(self._read_yaml)
         except Exception as e:
             logger.error(f"Failed to load local dataset from {self.file_path}: {e}")
             raise
@@ -111,6 +111,15 @@ async def _parse_metadata_async(self) -> SeedDatasetMetadata | None:
         SeedDatasetMetadata._validate_singular_fields(metadata=result)
         return result
 
+    def _read_yaml(self) -> Any:
+        """
+        Read and parse the local dataset YAML file.
+
+        Returns:
+            Any: Parsed YAML content.
+        """
+        return yaml.safe_load(self.file_path.read_text(encoding="utf-8"))
+
 
 def _register_local_datasets() -> None:
     """

tests/unit/datasets/test_local_dataset_loader.py

@@ -2,11 +2,12 @@
 # Licensed under the MIT license.
 
 from pathlib import Path
+from unittest.mock import AsyncMock, MagicMock, patch
 
 import pytest
 
 from pyrit.datasets.seed_datasets.local.local_dataset_loader import _LocalDatasetLoader
-from pyrit.models import SeedDataset
+from pyrit.models import SeedDataset, SeedPrompt
 
 
 class TestLocalDatasetLoader:
@@ -49,6 +50,59 @@ async def test_fetch_dataset(self, tmp_path, valid_yaml_content):
         assert len(dataset.prompts) == 1
         assert dataset.prompts[0].value == "test prompt"
 
+    async def test_fetch_dataset_offloads_file_read(self, tmp_path: Path) -> None:
+        """Dataset file loading runs outside the event loop thread."""
+        file_path = tmp_path / "test.yaml"
+        loader = _LocalDatasetLoader.__new__(_LocalDatasetLoader)
+        loader.file_path = file_path
+        loader._dataset_name = "test_dataset"
+        expected = SeedDataset(
+            dataset_name="test_dataset",
+            seeds=[SeedPrompt(value="test prompt", data_type="text")],
+        )
+        to_thread_mock = AsyncMock(return_value=expected)
+
+        with (
+            patch.object(SeedDataset, "from_yaml_file") as load_mock,
+            patch(
+                "pyrit.datasets.seed_datasets.local.local_dataset_loader.asyncio.to_thread",
+                new=to_thread_mock,
+            ),
+        ):
+            dataset = await loader.fetch_dataset_async()
+
+        assert dataset is expected
+        to_thread_mock.assert_awaited_once_with(load_mock, file_path)
+        load_mock.assert_not_called()
+
+    async def test_parse_metadata_offloads_file_read(self, tmp_path: Path) -> None:
+        """Metadata YAML parsing runs outside the event loop thread."""
+        file_path = tmp_path / "test.yaml"
+        loader = _LocalDatasetLoader.__new__(_LocalDatasetLoader)
+        loader.file_path = file_path
+        loader._dataset_name = "test_dataset"
+        read_yaml_mock = MagicMock(
+            return_value={
+                "dataset_name": "test_dataset",
+                "harm_categories": ["violence"],
+            }
+        )
+        to_thread_mock = AsyncMock(return_value=read_yaml_mock.return_value)
+
+        with (
+            patch.object(loader, "_read_yaml", new=read_yaml_mock),
+            patch(
+                "pyrit.datasets.seed_datasets.local.local_dataset_loader.asyncio.to_thread",
+                new=to_thread_mock,
+            ),
+        ):
+            metadata = await loader._parse_metadata_async()
+
+        assert metadata is not None
+        assert metadata.harm_categories == {"violence"}
+        to_thread_mock.assert_awaited_once_with(read_yaml_mock)
+        read_yaml_mock.assert_not_called()
+
     async def test_fetch_dataset_file_not_found(self):
         loader = _LocalDatasetLoader(file_path=Path("non_existent.yaml"))
         with pytest.raises(Exception):