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.core;
  
  import org.apache.beam.sdk.state.State;
  import org.apache.beam.sdk.state.StateContext;
  import org.apache.beam.sdk.state.StateContexts;
  import org.apache.beam.sdk.transforms.GroupByKey;
  
  /**
   * {@code StateInternals} describes the functionality a runner needs to provide for the State API to
   * be supported.
   *
   * <p>The SDK will only use this after elements have been partitioned by key. For instance, after a
   * {@link GroupByKey} operation. The runner implementation must ensure that any writes using {@link
   * StateInternals} are implicitly scoped to the key being processed and the specific step accessing
   * state.
   *
   * <p>The runner implementation must also ensure that any writes to the associated state objects are
   * persisted together with the completion status of the processing that produced these writes.
   *
   * <p>This is a low-level API intended for use by the Beam SDK. It should not be used directly, and
   * is highly likely to change.
   */
  public interface StateInternals {
  
    /** The key for this {@link StateInternals}. */
    Object getKey();
  
    /** Return the state associated with {@code address} in the specified {@code namespace}. */
    default <T extends State> T state(StateNamespace namespace, StateTag<T> address) {
      return state(namespace, address, StateContexts.nullContext());
    }
  
    /**
     * Return the state associated with {@code address} in the specified {@code namespace} with the
     * {@link StateContext}.
     */
    <T extends State> T state(StateNamespace namespace, StateTag<T> address, StateContext<?> c);
  }
  