content: /*
   * 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.
   */
  package org.apache.beam.runners.direct;
  
  import org.apache.beam.sdk.Pipeline;
  import org.apache.beam.sdk.io.Read;
  import org.apache.beam.sdk.runners.AppliedPTransform;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /**
   * A factory for creating instances of {@link TransformEvaluator} for the application of a {@link
   * PTransform}.
   *
   * <p>{@link TransformEvaluatorFactory TransformEvaluatorFactories} will be reused within a single
   * execution of a {@link Pipeline} but will not be reused across executions.
   */
  interface TransformEvaluatorFactory {
    /**
     * Create a new {@link TransformEvaluator} for the application of the {@link PTransform}.
     *
     * <p>Any work that must be done before input elements are processed (such as calling {@code
     * DoFn.StartBundle}) must be done before the {@link TransformEvaluator} is made available to the
     * caller.
     *
     * <p>May return null if the application cannot produce an evaluator (for example, it is a {@link
     * Read} {@link PTransform} where all evaluators are in-use).
     *
     * @return An evaluator capable of processing the transform on the bundle, or null if no evaluator
     *     can be constructed.
     * @throws Exception whenever constructing the underlying evaluator throws an exception
     */
    @Nullable
    <InputT> TransformEvaluator<InputT> forApplication(
        AppliedPTransform<?, ?, ?> application, CommittedBundle<?> inputBundle) throws Exception;
  
    /**
     * Cleans up any state maintained by this {@link TransformEvaluatorFactory}. Called after a {@link
     * Pipeline} is shut down. No more calls to {@link #forApplication(AppliedPTransform,
     * CommittedBundle)} will be made after a call to {@link #cleanup()}.
     */
    void cleanup() throws Exception;
  }
  