flink-core/src/main/java/org/apache/flink/core/fs/RecoverableFsDataOutputStream.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.core.fs;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.core.fs.RecoverableWriter.CommitRecoverable;
import org.apache.flink.core.fs.RecoverableWriter.ResumeRecoverable;

import java.io.IOException;

/**
 * An output stream to a file system that can be recovered at well defined points.
 * The stream initially writes to hidden files or temp files and only creates the
 * target file once it is closed and "committed".
 */
@PublicEvolving
public abstract class RecoverableFsDataOutputStream extends FSDataOutputStream {

	/**
	 * Ensures all data so far is persistent (similar to {@link #sync()}) and returns
	 * a handle to recover the stream at the current position.
	 */
	public abstract ResumeRecoverable persist() throws IOException;

	/**
	 * Closes the stream, ensuring persistence of all data (similar to {@link #sync()}).
	 * This returns a Committer that can be used to publish (make visible) the file
	 * that the stream was writing to.
	 */
	public abstract Committer closeForCommit() throws IOException;

	/**
	 * Closes this stream. Closing the steam releases the local resources that the stream
	 * uses, but does NOT result in durability of previously written data. This method
	 * should be interpreted as a "close in order to dispose" or "close on failure".
	 *
	 * <p>In order to persist all previously written data, one needs to call the
	 * {@link #closeForCommit()} method and call {@link Committer#commit()} on the retured
	 * committer object.
	 *
	 * @throws IOException Thrown if an error occurred during closing.
	 */
	@Override
	public abstract void close() throws IOException;

	// ------------------------------------------------------------------------

	/**
	 * A committer can publish the file of a stream that was closed.
	 * The Committer can be recovered via a {@link CommitRecoverable}.
	 */
	public interface Committer {

		/**
		 * Commits the file, making it visible. The file will contain the exact data
		 * as when the committer was created.
		 *
		 * @throws IOException Thrown if committing fails.
		 */
		void commit() throws IOException;

		/**
		 * Commits the file, making it visible. The file will contain the exact data
		 * as when the committer was created.
		 *
		 * <p>This method tolerates situations where the file was already committed and
		 * will not raise an exception in that case. This is important for idempotent
		 * commit retries as they need to happen after recovery.
		 *
		 * @throws IOException Thrown if committing fails.
		 */
		void commitAfterRecovery() throws IOException;

		/**
		 * Gets a recoverable object to recover the committer. The recovered committer
		 * will commit the file with the exact same data as this committer would commit
		 * it.
		 */
		CommitRecoverable getRecoverable();
	}
}