statefun-flink/statefun-flink-state-processor/src/main/java/org/apache/flink/statefun/flink/state/processor/StateBootstrapFunction.java

/*
 * 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.flink.statefun.flink.state.processor;

import org.apache.flink.statefun.sdk.Address;
import org.apache.flink.statefun.sdk.StatefulFunction;

/**
 * A {@link StateBootstrapFunction} defines how to bootstrap state for a {@link StatefulFunction}
 * instance with a given input.
 *
 * <p>Each {@code StateBootstrapFunction} instance directly corresponds to a {@code
 * StatefulFunction} instance. Likewise, each instance is uniquely identified by an {@link Address},
 * represented by the type and id of the function being bootstrapped. Any state that is persisted by
 * a {@code StateBootstrapFunction} instance will be available to the corresponding live {@code
 * StatefulFunction} instance having the same address.
 *
 * <p>For example, consider the following state bootstrap function:
 *
 * <pre>{@code
 * public class MyStateBootstrapFunction implements StateBootstrapFunction {
 *
 *     {@code @Persisted}
 *     private PersistedValue<MyState> state = PersistedValue.of("my-state", MyState.class);
 *
 *     {@code @Override}
 *     public void bootstrap(Context context, Object input) {
 *         state.set(extractStateFromInput(input));
 *     }
 * }
 * }</pre>
 *
 * <p>Assume that this bootstrap function was provided for function type {@literal MyFunctionType},
 * and the id of the bootstrap function instance was {@literal id-13}. The function writes persisted
 * state of name {@literal my-state} using the given bootstrap data. After restoring a Stateful
 * Functions application from the savepoint generated using this bootstrap function, the stateful
 * function instance with address {@literal (MyFunctionType, id-13)} will already have state values
 * available under state name {@literal my-state}.
 */
public interface StateBootstrapFunction {

  /**
   * Bootstraps state for this function with the given bootstrap data.
   *
   * @param context context for the current bootstrap invocation. The provided context instance
   *     should not be used outside the scope of the current invocation.
   * @param bootstrapData input to be used for bootstrapping state.
   */
  void bootstrap(Context context, Object bootstrapData);
}