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

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

zhtaoxiang commented on code in PR #10528:
URL: https://github.com/apache/pinot/pull/10528#discussion_r1218368394


##########
pinot-segment-spi/src/main/java/org/apache/pinot/segment/spi/memory/unsafe/MmapMemory.java:
##########
@@ -0,0 +1,377 @@
+/**
+ * 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;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+/**
+ * A {@link Memory} that whose bytes are mapped on a file.
+ */
+public class MmapMemory implements Memory {
+  private static final Logger LOGGER = LoggerFactory.getLogger(MmapMemory.class);
+
+  private static final MapFun MAP_FUN;
+
+  /**
+   * The address that correspond to the offset given at creation time.
+   *
+   * The actual mapping address may be smaller than this value, as usually memory map must start on an address that is
+   * page aligned.
+   */
+  private final long _address;
+  /**
+   * 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;
+  private boolean _closed = false;
+
+  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;
+
+    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(_address, _size, mode);
+  }
+
+  @Override
+  public void close()
+      throws IOException {
+    try {
+      if (!_closed) {
+        synchronized (this) {
+          if (!_closed) {
+            _section._unmapFun.unmap();
+            _closed = true;
+          }
+        }
+      }
+    } catch (InvocationTargetException | IllegalAccessException e) {
+      throw new RuntimeException("Error while calling unmap", e);
+    }
+  }
+
+  @Override
+  protected void finalize()
+      throws Throwable {
+    if (!_closed) {
+      LOGGER.warn("Mmap section of " + _size + " wasn't explicitly closed");
+      close();
+    }
+    super.finalize();
+  }
+
+  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;
+    }
+  }
+
+  /**
+   * This is a factory method that can be used to create {@link MapSection}s.
+   *
+   * Each JVM may provide different method to map files in memory.
+   */
+  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(),
+          new Map0Fun.Java11(),
+          new Map0Fun.Java17(),
+          new Map0Fun.Java20()
+      );
+
+      for (Finder<? extends MapFun> candidate : candidates) {
+        try {
+          return candidate.tryFind();
+        } catch (NoSuchMethodException | ClassNotFoundException | AssertionError e) {
+          // IGNORE
+        }
+      }
+      throw new NoSuchMethodException("Cannot find how to create memory map files in Java " + JavaVersion.VERSION);
+    }
+  }
+
+  /**
+   * As defined by POSIX, the map0 method requires that the offset is page aligned. Failing to do that may produce
+   * segfault errors. This interface is a {@link MapFun} that does some sanitation before calling the map method.
+   * They include:
+   * <ul>
+   *   <li>Grow the file if the last mapped byte is larger than the file length.</li>
+   *   <li>Align the offset with the previous page. This means that we need to correct the actual mapped address.</li>
+   * </ul>
+   */
+  interface Map0Fun extends MapFun {
+
+    /**
+     * @param pageAlignedOffset It has to be a positive value that is page aligned.
+     */
+    MapSection map0(FileChannel fc, boolean readOnly, long pageAlignedOffset, long size)

Review Comment:
   a beginner question: where is this method implemented? 



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