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/*
 * 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.runtime.state;

import org.apache.flink.annotation.Internal;
import org.apache.flink.runtime.checkpoint.CheckpointOptions;

import javax.annotation.Nonnull;

import java.util.concurrent.RunnableFuture;

/**
 * Interface for different snapshot approaches in state backends. Implementing classes should ideally be stateless or at
 * least threadsafe, i.e. this is a functional interface and is can be called in parallel by multiple checkpoints.
 *
 * @param  type of the returned state object that represents the result of the snapshot operation.
 */
@Internal
public interface SnapshotStrategy {

	/**
	 * Operation that writes a snapshot into a stream that is provided by the given {@link CheckpointStreamFactory} and
	 * returns a @{@link RunnableFuture} that gives a state handle to the snapshot. It is up to the implementation if
	 * the operation is performed synchronous or asynchronous. In the later case, the returned Runnable must be executed
	 * first before obtaining the handle.
	 *
	 * @param checkpointId      The ID of the checkpoint.
	 * @param timestamp         The timestamp of the checkpoint.
	 * @param streamFactory     The factory that we can use for writing our state to streams.
	 * @param checkpointOptions Options for how to perform this checkpoint.
	 * @return A runnable future that will yield a {@link StateObject}.
	 */
	@Nonnull
	RunnableFuture snapshot(
		long checkpointId,
		long timestamp,
		@Nonnull CheckpointStreamFactory streamFactory,
		@Nonnull CheckpointOptions checkpointOptions) throws Exception;
}