Add support for loading torchscript models

CHANGES.md

@@ -65,6 +65,8 @@
 * Add UDF metrics support for Samza portable mode.
 * Option for SparkRunner to avoid the need of SDF output to fit in memory ([#23852](https://github.com/apache/beam/issues/23852)).
   This helps e.g. with ParquetIO reads. Turn the feature on by adding experiment `use_bounded_concurrent_output_for_sdf`.
+* Add support for loading TorchScript models with `PytorchModelHandler`. The TorchScript model path can be
+  passed to PytorchModelHandler using `torch_script_model_path=<path_to_model>`. ([#25321](https://github.com/apache/beam/pull/25321))
 
 ## Breaking Changes
 

sdks/python/apache_beam/ml/inference/base.py

@@ -174,6 +174,12 @@ def update_model_path(self, model_path: Optional[str] = None):
     """Update the model paths produced by side inputs."""
     pass
 
+  def validate_constructor_args(self):
+    """
+    Validate arguments passed to the ModelHandler constructor.
+    """
+    raise NotImplementedError
+
 
 class KeyedModelHandler(Generic[KeyT, ExampleT, PredictionT, ModelT],
                         ModelHandler[Tuple[KeyT, ExampleT],

sdks/python/apache_beam/ml/inference/pytorch_inference.py

@@ -57,32 +57,66 @@
                                   Iterable[PredictionResult]]
 
 
-def _load_model(
-    model_class: torch.nn.Module, state_dict_path, device, **model_params):
-  model = model_class(**model_params)
+def _validate_constructor_args(
+    state_dict_path, model_class, torch_script_model_path):
+  message = (
+      "A {param1} has been supplied to the model "
+      "handler, but the required {param2} is missing. "
+      "Please provide the {param2} in order to "
+      "successfully load the {param1}.")
+  # state_dict_path and model_class are coupled with each other
+  # raise RuntimeError if user forgets to pass any one of them.
+  if state_dict_path and not model_class:
+    raise RuntimeError(
+        message.format(param1="state_dict_path", param2="model_class"))
+
+  if not state_dict_path and model_class:
+    raise RuntimeError(
+        message.format(param1="model_class", param2="state_dict_path"))
+
+  if torch_script_model_path and state_dict_path:
+    raise RuntimeError(
+        "Please specify either torch_script_model_path or "
+        "(state_dict_path, model_class) to successfully load the model.")
+
 
+def _load_model(
+    model_class: Optional[Callable[..., torch.nn.Module]],
+    state_dict_path: Optional[str],
+    device: torch.device,
+    model_params: Optional[Dict[str, Any]],
+    torch_script_model_path: Optional[str]):
   if device == torch.device('cuda') and not torch.cuda.is_available():
     logging.warning(
-        "Model handler specified a 'GPU' device, but GPUs are not available. " \
+        "Model handler specified a 'GPU' device, but GPUs are not available. "
         "Switching to CPU.")
     device = torch.device('cpu')
 
-  file = FileSystems.open(state_dict_path, 'rb')
   try:
     logging.info(
         "Loading state_dict_path %s onto a %s device", state_dict_path, device)
-    state_dict = torch.load(file, map_location=device)
+    if not torch_script_model_path:
+      file = FileSystems.open(state_dict_path, 'rb')
+      model = model_class(**model_params)  # type: ignore[misc]
+      state_dict = torch.load(file, map_location=device)
+      model.load_state_dict(state_dict)
+    else:
+      file = FileSystems.open(torch_script_model_path, 'rb')
+      model = torch.jit.load(file, map_location=device)
   except RuntimeError as e:
     if device == torch.device('cuda'):
       message = "Loading the model onto a GPU device failed due to an " \
         f"exception:\n{e}\nAttempting to load onto a CPU device instead."
       logging.warning(message)
       return _load_model(
-          model_class, state_dict_path, torch.device('cpu'), **model_params)
+          model_class,
+          state_dict_path,
+          torch.device('cpu'),
+          model_params,
+          torch_script_model_path)
     else:
       raise e
 
-  model.load_state_dict(state_dict)
   model.to(device)
   model.eval()
   logging.info("Finished loading PyTorch model.")
@@ -148,19 +182,23 @@ class PytorchModelHandlerTensor(ModelHandler[torch.Tensor,
                                              torch.nn.Module]):
   def __init__(
       self,
-      state_dict_path: str,
-      model_class: Callable[..., torch.nn.Module],
-      model_params: Dict[str, Any],
+      state_dict_path: Optional[str] = None,
+      model_class: Optional[Callable[..., torch.nn.Module]] = None,
+      model_params: Optional[Dict[str, Any]] = None,
       device: str = 'CPU',
       *,
       inference_fn: TensorInferenceFn = default_tensor_inference_fn,
+      torch_script_model_path: Optional[str] = None,
       min_batch_size: Optional[int] = None,
       max_batch_size: Optional[int] = None):
     """Implementation of the ModelHandler interface for PyTorch.
 
-    Example Usage::
-
-      pcoll | RunInference(PytorchModelHandlerTensor(state_dict_path="my_uri"))
+    Example Usage for torch model::
+      pcoll | RunInference(PytorchModelHandlerTensor(state_dict_path="my_uri",
+                                                     model_class="my_class"))
+    Example Usage for torchscript model::
+      pcoll | RunInference(PytorchModelHandlerTensor(
+        torch_script_model_path="my_uri"))
 
     See https://pytorch.org/tutorials/beginner/saving_loading_models.html
     for details
@@ -176,6 +214,10 @@ def __init__(
         Otherwise, it will be CPU.
       inference_fn: the inference function to use during RunInference.
         default=_default_tensor_inference_fn
+      torch_script_model_path: Path to the torch script model.
+         the model will be loaded using `torch.jit.load()`.
+        `state_dict_path`, `model_class` and `model_params`
+         arguments will be disregarded.
       min_batch_size: the minimum batch size to use when batching inputs. This
         batch will be fed into the inference_fn as a Sequence of Tensors.
       max_batch_size: the maximum batch size to use when batching inputs. This
@@ -192,26 +234,42 @@ def __init__(
       logging.info("Device is set to CPU")
       self._device = torch.device('cpu')
     self._model_class = model_class
-    self._model_params = model_params
+    self._model_params = model_params if model_params else {}
     self._inference_fn = inference_fn
     self._batching_kwargs = {}
     if min_batch_size is not None:
       self._batching_kwargs['min_batch_size'] = min_batch_size
     if max_batch_size is not None:
       self._batching_kwargs['max_batch_size'] = max_batch_size
+    self._torch_script_model_path = torch_script_model_path
+
+    self.validate_constructor_args()
+
+  def validate_constructor_args(self):
+    _validate_constructor_args(
+        state_dict_path=self._state_dict_path,
+        model_class=self._model_class,
+        torch_script_model_path=self._torch_script_model_path)
 
   def load_model(self) -> torch.nn.Module:
     """Loads and initializes a Pytorch model for processing."""
     model, device = _load_model(
         self._model_class,
         self._state_dict_path,
         self._device,
-        **self._model_params)
+        self._model_params,
+        self._torch_script_model_path
+    )
     self._device = device
     return model
 
   def update_model_path(self, model_path: Optional[str] = None):
-    self._state_dict_path = model_path if model_path else self._state_dict_path
+    if self._torch_script_model_path:
+      self._torch_script_model_path = (
+          model_path if model_path else self._torch_script_model_path)
+    else:
+      self._state_dict_path = (
+          model_path if model_path else self._state_dict_path)
 
   def run_inference(
       self,
@@ -240,9 +298,11 @@ def run_inference(
       An Iterable of type PredictionResult.
     """
     inference_args = {} if not inference_args else inference_args
-
+    model_id = (
+        self._state_dict_path
+        if not self._torch_script_model_path else self._torch_script_model_path)
     return self._inference_fn(
-        batch, model, self._device, inference_args, self._state_dict_path)
+        batch, model, self._device, inference_args, model_id)
 
   def get_num_bytes(self, batch: Sequence[torch.Tensor]) -> int:
     """
@@ -336,20 +396,25 @@ class PytorchModelHandlerKeyedTensor(ModelHandler[Dict[str, torch.Tensor],
                                                   torch.nn.Module]):
   def __init__(
       self,
-      state_dict_path: str,
-      model_class: Callable[..., torch.nn.Module],
-      model_params: Dict[str, Any],
+      state_dict_path: Optional[str] = None,
+      model_class: Optional[Callable[..., torch.nn.Module]] = None,
+      model_params: Optional[Dict[str, Any]] = None,
       device: str = 'CPU',
       *,
       inference_fn: KeyedTensorInferenceFn = default_keyed_tensor_inference_fn,
+      torch_script_model_path: Optional[str] = None,
       min_batch_size: Optional[int] = None,
       max_batch_size: Optional[int] = None):
     """Implementation of the ModelHandler interface for PyTorch.
 
-    Example Usage::
+     Example Usage for torch model::
+      pcoll | RunInference(PytorchModelHandlerKeyedTensor(
+        state_dict_path="my_uri",
+        model_class="my_class"))
 
-      pcoll | RunInference(
-      PytorchModelHandlerKeyedTensor(state_dict_path="my_uri"))
+    Example Usage for torchscript model::
+      pcoll | RunInference(PytorchModelHandlerKeyedTensor(
+        torch_script_model_path="my_uri"))
 
     **NOTE:** This API and its implementation are under development and
     do not provide backward compatibility guarantees.
@@ -368,6 +433,10 @@ def __init__(
         Otherwise, it will be CPU.
       inference_fn: the function to invoke on run_inference.
         default = default_keyed_tensor_inference_fn
+      torch_script_model_path: Path to the torch script model.
+         the model will be loaded using `torch.jit.load()`.
+        `state_dict_path`, `model_class` and `model_params`
+         arguments will be disregarded..
       min_batch_size: the minimum batch size to use when batching inputs. This
         batch will be fed into the inference_fn as a Sequence of Keyed Tensors.
       max_batch_size: the maximum batch size to use when batching inputs. This
@@ -385,26 +454,42 @@ def __init__(
       logging.info("Device is set to CPU")
       self._device = torch.device('cpu')
     self._model_class = model_class
-    self._model_params = model_params
+    self._model_params = model_params if model_params else {}
     self._inference_fn = inference_fn
     self._batching_kwargs = {}
     if min_batch_size is not None:
       self._batching_kwargs['min_batch_size'] = min_batch_size
     if max_batch_size is not None:
       self._batching_kwargs['max_batch_size'] = max_batch_size
+    self._torch_script_model_path = torch_script_model_path
+
+    self.validate_constructor_args()
+
+  def validate_constructor_args(self):
+    _validate_constructor_args(
+        state_dict_path=self._state_dict_path,
+        model_class=self._model_class,
+        torch_script_model_path=self._torch_script_model_path)
 
   def load_model(self) -> torch.nn.Module:
     """Loads and initializes a Pytorch model for processing."""
     model, device = _load_model(
         self._model_class,
         self._state_dict_path,
         self._device,
-        **self._model_params)
+        self._model_params,
+        self._torch_script_model_path
+    )
     self._device = device
     return model
 
   def update_model_path(self, model_path: Optional[str] = None):
-    self._state_dict_path = model_path if model_path else self._state_dict_path
+    if self._torch_script_model_path:
+      self._torch_script_model_path = (
+          model_path if model_path else self._torch_script_model_path)
+    else:
+      self._state_dict_path = (
+          model_path if model_path else self._state_dict_path)
 
   def run_inference(
       self,
@@ -433,9 +518,11 @@ def run_inference(
       An Iterable of type PredictionResult.
     """
     inference_args = {} if not inference_args else inference_args
-
+    model_id = (
+        self._state_dict_path
+        if not self._torch_script_model_path else self._torch_script_model_path)
     return self._inference_fn(
-        batch, model, self._device, inference_args, self._state_dict_path)
+        batch, model, self._device, inference_args, model_id)
 
   def get_num_bytes(self, batch: Sequence[torch.Tensor]) -> int:
     """