[GitHub] [pinot] gortiz commented on a diff in pull request #10528: PinotBufferFactory and a buffer implementation that uses Unsafe

["gortiz (via GitHub)" <gi...@apache.org>]

gortiz commented on code in PR #10528:
URL: https://github.com/apache/pinot/pull/10528#discussion_r1206374166


##########
pinot-segment-spi/src/main/java/org/apache/pinot/segment/spi/memory/unsafe/MmapMemory.java:
##########
@@ -0,0 +1,348 @@
+/**
+ * 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.pinot.segment.spi.memory.unsafe;
+
+import com.google.common.collect.Lists;
+import java.io.File;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.io.UncheckedIOException;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.nio.channels.FileChannel;
+import java.util.List;
+import java.util.function.BiConsumer;
+import net.openhft.chronicle.core.Jvm;
+import net.openhft.chronicle.core.OS;
+import net.openhft.posix.MSyncFlag;
+import net.openhft.posix.PosixAPI;
+import org.apache.pinot.segment.spi.utils.JavaVersion;
+
+
+public class MmapMemory implements Memory {
+
+  private static final MapFun MAP_FUN;
+
+  /**
+   * The address actually mapped. It has to be page aligned.
+   *
+   * {@code _address = _offset - offset % pageSize}
+   */
+  private final long _address;
+  /**
+   * The offset requested to map.
+   *
+   * {@code _address = _offset - offset % pageSize}
+   */
+  private final long _offset;
+  /**
+   * How many bytes have been requested to be mapped.
+   * The actual mapped size may be larger (up to the next page), but the actual mapped size
+   * is stored by {@link #_section}.
+   */
+  private final long _size;
+  private final MapSection _section;
+
+  static {
+    try {
+      Jvm.init();
+      MAP_FUN = MapFun.find();
+    } catch (ClassNotFoundException | NoSuchMethodException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  public MmapMemory(File file, boolean readOnly, long offset, long size) {
+    _size = size;
+    _offset = offset;
+
+    try {
+      _section = MAP_FUN.map(file, readOnly, offset, size);
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+    _address = _section.getAddress();
+  }
+
+  @Override
+  public long getAddress() {
+    return _address;
+  }
+
+  @Override
+  public long getSize() {
+    return _size;
+  }
+
+  @Override
+  public void flush() {
+    MSyncFlag mode = MSyncFlag.MS_SYNC;
+    PosixAPI.posix().msync(_offset, _size, mode);
+  }
+
+  @Override
+  public void close()
+      throws IOException {
+    try {
+      _section._unmapFun.unmap();
+    } catch (InvocationTargetException | IllegalAccessException e) {
+      throw new RuntimeException("Error while calling unmap", e);
+    }
+  }
+
+  private static class MapSection {
+    public static final MapSection EMPTY = new MapSection(0, () -> {
+    });
+    private final long _address;
+    private final UnmapFun _unmapFun;
+
+    public MapSection(long address, UnmapFun unmapFun) {
+      _address = address;
+      _unmapFun = unmapFun;
+    }
+
+    public long getAddress() {
+      return _address;
+    }
+
+    public UnmapFun getUnmapFun() {
+      return _unmapFun;
+    }
+  }
+
+  interface MapFun {
+
+    /**
+     * @param file The file to be mapped. If its length is lower than offset + size and the mode is not read only,
+     *            the file will be resized to that size.
+     * @param offset The offset in the file. Any positive value is valid, even if it is larger than the file size.
+     * @param size How many bytes to map.
+     * @throws IOException in several situations. For example, if the offset + size is larger than file length and the
+     * mode is read only or if the process doesn't have permission to read or modify the file.
+     */
+    MapSection map(File file, boolean readOnly, long offset, long size) throws IOException;
+
+    static MapFun find()
+        throws ClassNotFoundException, NoSuchMethodException {
+      List<Finder<? extends MapFun>> candidates = Lists.newArrayList(
+          new Map0Fun.ChronicleCore(),

Review Comment:
   With this ChronicleCore library we could remove all other options. They are already doing more or less the same thing we do here (taking care of more details and with more expertise than I have). We should decide whether we want to use their library (and remove `Map0Fun.Java11`, `Map0Fun.Java17` and `Java20`) or reinvent the wheel with the other `MapFun`.



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