Github user StefanRRichter commented on a diff in the pull request: https://github.com/apache/flink/pull/5239#discussion_r170266913 --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/state/DuplicatingCheckpointOutputStream.java --- @@ -0,0 +1,287 @@ +/* + * 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.VisibleForTesting; +import org.apache.flink.util.ExceptionUtils; +import org.apache.flink.util.Preconditions; + +import java.io.IOException; + +/** + * A CheckpointStateOutputStream that wraps a primary and a secondary CheckpointStateOutputStream and duplicates + * all writes into both streams. This stream applies buffering to reduce the amount of dual-method calling. Furthermore, + * exceptions that happen in interactions with the secondary stream are not exposed, until the user calls + * {@link #closeAndGetSecondaryHandle()}. In contrast to that, exceptions from interactions with the primary stream + * are immediately returned to the user. This class is used to write state for local recovery as a local (secondary) + * copy of the (primary) state snapshot that is written to a (slower but highly-available) remote filesystem. + */ +public class DuplicatingCheckpointOutputStream extends CheckpointStreamFactory.CheckpointStateOutputStream { + + /** Flag if the positional alignment of both streams is checked after each operation. */ + private static final boolean STRICT_ALIGNMENT_CHECKS = false; + + /** Default buffer size of 8KB. */ + private static final int DEFAULT_BUFFER_SIZER = 8 * 1024; + + /** Write buffer. */ + private final byte[] buffer; + + /** Position in the write buffer. */ + private int bufferIdx; + + /** + * Primary stream for writing the checkpoint data. Failures from this stream are forwarded. + */ + private final CheckpointStreamFactory.CheckpointStateOutputStream primaryOutputStream; + + /** + * Primary stream for writing the checkpoint data. Failures from this stream are not forwarded until + * {@link #closeAndGetSecondaryHandle()}. + */ + private final CheckpointStreamFactory.CheckpointStateOutputStream secondaryOutputStream; + + /** + * Stores a potential exception that occurred while interacting with {@link #secondaryOutputStream} + */ + private IOException secondaryStreamException; + + public DuplicatingCheckpointOutputStream( + CheckpointStreamFactory.CheckpointStateOutputStream primaryOutputStream, + CheckpointStreamFactory.CheckpointStateOutputStream secondaryOutputStream) throws IOException { + this(primaryOutputStream, secondaryOutputStream, DEFAULT_BUFFER_SIZER); + } + + public DuplicatingCheckpointOutputStream( + CheckpointStreamFactory.CheckpointStateOutputStream primaryOutputStream, + CheckpointStreamFactory.CheckpointStateOutputStream secondaryOutputStream, + int bufferSize) throws IOException { + + this.primaryOutputStream = Preconditions.checkNotNull(primaryOutputStream); + this.secondaryOutputStream = Preconditions.checkNotNull(secondaryOutputStream); + + this.buffer = new byte[bufferSize]; + this.bufferIdx = 0; + + this.secondaryStreamException = null; + + checkForAlignedStreamPositions(); + } + + @Override + public void write(int b) throws IOException { + + if (buffer.length <= bufferIdx) { + flushInternalBuffer(); + } + + buffer[bufferIdx] = (byte) b; + ++bufferIdx; + } + + @Override + public void write(byte[] b) throws IOException { + + write(b, 0, b.length); + } + + @Override + public void write(byte[] b, int off, int len) throws IOException { + + if (buffer.length <= len) { + + flushInternalBuffer(); + writeThroughInternal(b, off, len); + } else { + + if (buffer.length < len + bufferIdx) { + flushInternalBuffer(); + } + + System.arraycopy(b, off, buffer, bufferIdx, len); + bufferIdx += len; + } + } + + @Override + public long getPos() throws IOException { + final long referencePos = primaryOutputStream.getPos(); + return referencePos + bufferIdx; + } + + @Override + public void flush() throws IOException { + + flushInternalBuffer(); + primaryOutputStream.flush(); + + if (secondaryStreamException == null) { + try { + secondaryOutputStream.flush(); + } catch (IOException flushEx) { + handleSecondaryStreamOnException(flushEx); + } + } + } + + @Override + public void sync() throws IOException { + + flushInternalBuffer(); + primaryOutputStream.sync(); + + if (secondaryStreamException == null) { + try { + secondaryOutputStream.sync(); + } catch (IOException syncEx) { + handleSecondaryStreamOnException(syncEx); + } + } + } + + @Override + public void close() throws IOException { + + IOException exCollector = null; + + try { + flushInternalBuffer(); + } catch (IOException flushEx) { + exCollector = flushEx; + } + + try { + primaryOutputStream.close(); + } catch (IOException closeEx) { + exCollector = ExceptionUtils.firstOrSuppressed(closeEx, exCollector); + } + + if (secondaryStreamException == null) { + try { + secondaryOutputStream.close(); + } catch (IOException closeEx) { + handleSecondaryStreamOnException(closeEx); + } + } + + if (exCollector != null) { + throw exCollector; + } + } + + private void checkForAlignedStreamPositions() throws IOException { + + final long primaryPos = primaryOutputStream.getPos(); + + if (secondaryStreamException != null) { + return; --- End diff -- ð
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