yeandy commented on a change in pull request #16970:
URL: https://github.com/apache/beam/pull/16970#discussion_r821798777



##########
File path: sdks/python/apache_beam/ml/inference/base.py
##########
@@ -0,0 +1,222 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import logging
+import platform
+import resource
+import sys
+import time
+from typing import Any
+from typing import Iterable
+
+import apache_beam as beam
+from apache_beam.utils import shared
+from apache_beam.ml.inference.api import PredictionResult
+
+_MILLISECOND_TO_MICROSECOND = 1000
+_MICROSECOND_TO_NANOSECOND = 1000
+_SECOND_TO_MICROSECOND = 1000000
+
+
+def _unbatch(maybe_keyed_batches: Any):
+  keys, results = maybe_keyed_batches
+  if keys:
+    return zip(keys, results)
+  else:
+    return results
+
+
+class ModelLoader:
+  """Has the ability to load an ML model."""
+  def load_model(self):
+    """Loads an initializes a model for processing."""
+    raise NotImplementedError(type(self))
+
+
+class InferenceRunner:
+  """Implements running inferences for a framework."""
+  def run_inference(self, batch: Any, model: Any) -> 
Iterable[PredictionResult]:
+    """Runs inferences on a batch of examples and returns an Iterable of 
Predictions."""
+    raise NotImplementedError(type(self))
+
+
+class MetricsCollector:
+  """A metrics collector that tracks ML related performance and memory 
usage."""
+  def __init__(self, namespace: str):
+    # Metrics
+    self._inference_counter = beam.metrics.Metrics.counter(
+        namespace, 'num_inferences')
+    self._inference_request_batch_size = beam.metrics.Metrics.distribution(
+        namespace, 'inference_request_batch_size')
+    self._inference_request_batch_byte_size = (
+        beam.metrics.Metrics.distribution(
+            namespace, 'inference_request_batch_byte_size'))
+    # Batch inference latency in microseconds.
+    self._inference_batch_latency_micro_secs = (
+        beam.metrics.Metrics.distribution(
+            namespace, 'inference_batch_latency_micro_secs'))
+    self._model_byte_size = beam.metrics.Metrics.distribution(
+        namespace, 'model_byte_size')
+    # Model load latency in milliseconds.
+    self._load_model_latency_milli_secs = beam.metrics.Metrics.distribution(
+        namespace, 'load_model_latency_milli_secs')
+
+    # Metrics cache
+    self.load_model_latency_milli_secs_cache = None
+    self.model_byte_size_cache = None
+
+  def update_metrics_with_cache(self):
+    if self.load_model_latency_milli_secs_cache is not None:
+      self._load_model_latency_milli_secs.update(
+          self.load_model_latency_milli_secs_cache)
+      self.load_model_latency_milli_secs_cache = None
+    if self.model_byte_size_cache is not None:
+      self._model_byte_size.update(self.model_byte_size_cache)
+      self.model_byte_size_cache = None
+
+  def update(
+      self,
+      examples_count: int,
+      examples_byte_size: int,
+      latency_micro_secs: int):
+    self._inference_batch_latency_micro_secs.update(latency_micro_secs)
+    self._inference_counter.inc(examples_count)
+    self._inference_request_batch_size.update(examples_count)
+    self._inference_request_batch_byte_size.update(examples_byte_size)
+
+
+class RunInferenceDoFn(beam.DoFn):
+  def __init__(self, model_loader, inference_runner, clock=None):
+    self._model_loader = model_loader
+    self._inference_runner = inference_runner
+    self._shared_model_handle = shared.Shared()
+    # TODO: Compute a good metrics namespace
+    self._metrics_collector = MetricsCollector('default_namespace')
+    self._clock = clock
+    if not clock:
+      self._clock = _ClockFactory.make_clock()
+    self._model = None
+
+  def _load_model(self):
+    def load():
+      """Function for constructing shared LoadedModel."""
+      memory_before = _get_current_process_memory_in_bytes()
+      start_time = self._clock.get_current_time_in_microseconds()
+      model = self._model_loader.load_model()
+      end_time = self._clock.get_current_time_in_microseconds()
+      memory_after = _get_current_process_memory_in_bytes()
+      self._metrics_collector.load_model_latency_milli_secs_cache = (
+          (end_time - start_time) / _MILLISECOND_TO_MICROSECOND)
+      self._metrics_collector.model_byte_size_cache = (
+          memory_after - memory_before)
+      return model
+
+    return self._shared_model_handle.acquire(load)
+
+  def setup(self):
+    super().setup()
+    self._model = self._load_model()
+
+  def process(self, batch):
+    has_keys = isinstance(batch[0], tuple)
+    start_time = self._clock.get_current_time_in_microseconds()
+    if has_keys:
+      examples = [example for _, example in batch]
+      keys = [key for key, _ in batch]
+    else:
+      examples = batch
+      keys = None
+    inference_generator = self._inference_runner.run_inference(
+        examples, self._model)
+    predictions = [
+        PredictionResult(e, r) for e, r in zip(examples, inference_generator)
+    ]
+    inference_latency = self._clock.get_current_time_in_microseconds(

Review comment:
       👍 




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