[GitHub] [flink] zhijiangW commented on a change in pull request #8880: [FLINK-12986] [network] Fix instability of BoundedBlockingSubpartition under memory pressure.

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zhijiangW commented on a change in pull request #8880: [FLINK-12986] [network] Fix instability of BoundedBlockingSubpartition under memory pressure.
URL: https://github.com/apache/flink/pull/8880#discussion_r298029284
 
 

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 File path: flink-runtime/src/main/java/org/apache/flink/runtime/io/network/partition/FileChannelMemoryMappedBoundedData.java
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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.io.network.partition;
+
+import org.apache.flink.runtime.io.network.buffer.Buffer;
+import org.apache.flink.util.IOUtils;
+
+import org.apache.flink.shaded.netty4.io.netty.util.internal.PlatformDependent;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileChannel.MapMode;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.StandardOpenOption;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.apache.flink.util.Preconditions.checkState;
+
+final class FileChannelMemoryMappedBoundedData implements BoundedData {
+
+	/** The file channel backing the memory mapped file. */
+	private final FileChannel fileChannel;
+
+	/** The reusable array with header buffer and data buffer, to use gathering writes on the
+	 * file channel ({@link java.nio.channels.GatheringByteChannel#write(ByteBuffer[])}). */
+	private final ByteBuffer[] headerAndBufferArray;
+
+	/** All memory mapped regions. */
+	private final ArrayList<ByteBuffer> memoryMappedRegions;
+
+	/** The path of the memory mapped file. */
+	private final Path filePath;
+
+	/** The position in the file channel. Cached for efficiency, because an actual position
+	 * lookup in the channel involves various locks and checks. */
+	private long pos;
+
+	/** The position where the current memory mapped region must end. */
+	private long endOfCurrentRegion;
+
+	/** The position where the current memory mapped started. */
+	private long startOfCurrentRegion;
+
+	/** The maximum size of each mapped region. */
+	private final long maxRegionSize;
+
+	FileChannelMemoryMappedBoundedData(
+			Path filePath,
+			FileChannel fileChannel,
+			int maxSizePerMappedRegion) throws IOException {
+
+		this.filePath = filePath;
+		this.fileChannel = fileChannel;
+		this.headerAndBufferArray = BufferReaderWriterUtil.allocatedWriteBufferArray();
+		this.memoryMappedRegions = new ArrayList<>(4);
+		this.maxRegionSize = maxSizePerMappedRegion;
+		this.endOfCurrentRegion = maxSizePerMappedRegion;
+	}
+
+	@Override
+	public void writeBuffer(Buffer buffer) throws IOException {
+		if (tryWriteBuffer(buffer)) {
+			return;
+		}
+
+		mapRegionAndStartNext();
+
+		if (!tryWriteBuffer(buffer)) {
+			throwTooLargeBuffer(buffer);
+		}
+	}
+
+	private boolean tryWriteBuffer(Buffer buffer) throws IOException {
+		final long spaceLeft = endOfCurrentRegion - pos;
+		final long bytesWritten = BufferReaderWriterUtil.writeToByteChannelIfBelowSize(
+				fileChannel, buffer, headerAndBufferArray, spaceLeft);
+
+		if (bytesWritten >= 0) {
+			pos += bytesWritten;
+			return true;
+		}
+		else {
+			return false;
+		}
+	}
+
+	@Override
+	public BoundedData.Reader createReader() {
+		checkState(!fileChannel.isOpen());
+
+		final List<ByteBuffer> buffers = memoryMappedRegions.stream()
+				.map((bb) -> bb.duplicate().order(ByteOrder.nativeOrder()))
+				.collect(Collectors.toList());
+
+		return new MemoryMappedBoundedData.BufferSlicer(buffers);
+	}
+
+	/**
+	 * Finishes the current region and prevents further writes.
+	 * After calling this method, further calls to {@link #writeBuffer(Buffer)} will fail.
+	 */
+	@Override
+	public void finishWrite() throws IOException {
+		mapRegionAndStartNext();
+		fileChannel.close();
+	}
+
+	/**
+	 * Closes the file and unmaps all memory mapped regions
+	 * After calling this method, access to any ByteBuffer obtained from this instance
+	 * will cause a segmentation fault.
+	 */
+	public void close() throws IOException {
+		IOUtils.closeQuietly(fileChannel);
+
+		for (ByteBuffer bb : memoryMappedRegions) {
+			PlatformDependent.freeDirectBuffer(bb);
+		}
+		memoryMappedRegions.clear();
+
+		// To make this compatible with all versions of Windows, we must wait with
+		// deleting the file until it is unmapped.
+		// See also https://stackoverflow.com/questions/11099295/file-flag-delete-on-close-and-memory-mapped-files/51649618#51649618
+
+		Files.delete(filePath);
+	}
+
+	@Override
+	public long getSize() {
+		return pos;
+	}
+
+	private void mapRegionAndStartNext() throws IOException {
+		final ByteBuffer region = fileChannel.map(MapMode.READ_ONLY, startOfCurrentRegion, pos - startOfCurrentRegion);
+		region.order(ByteOrder.nativeOrder());
+		memoryMappedRegions.add(region);
+
+		startOfCurrentRegion = pos;
+		endOfCurrentRegion = startOfCurrentRegion + maxRegionSize;
+	}
+
+	private void throwTooLargeBuffer(Buffer buffer) throws IOException {
+		throw new IOException(String.format(
+				"The buffer (%d bytes) is larger than the maximum size of a memory buffer (%d bytes)",
+				buffer.getSize(), maxRegionSize));
+	}
+
+	// ------------------------------------------------------------------------
+	//  Factories
+	// ------------------------------------------------------------------------
+
+	/**
+	 * Creates new MemoryMappedBuffers, creating a memory mapped file at the given path.
+	 */
+	public static FileChannelMemoryMappedBoundedData create(Path memMappedFilePath) throws IOException {
+		return createWithRegionSize(memMappedFilePath, Integer.MAX_VALUE);
 
 Review comment:
   checkNotNull(memMappedFilePath)?

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