[SPARK-15178][CORE] Remove LazyFileRegion instead use netty's DefaultFileRegion

## What changes were proposed in this pull request?
Remove LazyFileRegion instead use netty's DefaultFileRegion, since It was created so that we didn't create a file descriptor before having to send the file.

## How was this patch tested?
Existing tests

Author: Sandeep Singh <sandeep@techaddict.me>

Closes #12977 from techaddict/SPARK-15178.

common/network-common/src/main/java/org/apache/spark/network/buffer/FileSegmentManagedBuffer.java

@@ -130,7 +130,7 @@ public final class FileSegmentManagedBuffer extends ManagedBuffer {
   @Override
   public Object convertToNetty() throws IOException {
     if (conf.lazyFileDescriptor()) {
-      return new LazyFileRegion(file, offset, length);
+      return new DefaultFileRegion(file, offset, length);
     } else {
       FileChannel fileChannel = new FileInputStream(file).getChannel();
       return new DefaultFileRegion(fileChannel, offset, length);

common/network-common/src/main/java/org/apache/spark/network/buffer/LazyFileRegion.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.spark.network.buffer;
-
-import java.io.FileInputStream;
-import java.io.File;
-import java.io.IOException;
-import java.nio.channels.FileChannel;
-import java.nio.channels.WritableByteChannel;
-
-import com.google.common.base.Objects;
-import io.netty.channel.FileRegion;
-import io.netty.util.AbstractReferenceCounted;
-
-import org.apache.spark.network.util.JavaUtils;
-
-/**
- * A FileRegion implementation that only creates the file descriptor when the region is being
- * transferred. This cannot be used with Epoll because there is no native support for it.
- *
- * This is mostly copied from DefaultFileRegion implementation in Netty. In the future, we
- * should push this into Netty so the native Epoll transport can support this feature.
- */
-public final class LazyFileRegion extends AbstractReferenceCounted implements FileRegion {
-
-  private final File file;
-  private final long position;
-  private final long count;
-
-  private FileChannel channel;
-
-  private long numBytesTransferred = 0L;
-
-  /**
-   * @param file file to transfer.
-   * @param position start position for the transfer.
-   * @param count number of bytes to transfer starting from position.
-   */
-  public LazyFileRegion(File file, long position, long count) {
-    this.file = file;
-    this.position = position;
-    this.count = count;
-  }
-
-  @Override
-  protected void deallocate() {
-    JavaUtils.closeQuietly(channel);
-  }
-
-  @Override
-  public long position() {
-    return position;
-  }
-
-  @Override
-  public long transfered() {
-    return numBytesTransferred;
-  }
-
-  @Override
-  public long count() {
-    return count;
-  }
-
-  @Override
-  public long transferTo(WritableByteChannel target, long position) throws IOException {
-    if (channel == null) {
-      channel = new FileInputStream(file).getChannel();
-    }
-
-    long count = this.count - position;
-    if (count < 0 || position < 0) {
-      throw new IllegalArgumentException(
-          "position out of range: " + position + " (expected: 0 - " + (count - 1) + ')');
-    }
-
-    if (count == 0) {
-      return 0L;
-    }
-
-    long written = channel.transferTo(this.position + position, count, target);
-    if (written > 0) {
-      numBytesTransferred += written;
-    }
-    return written;
-  }
-
-  @Override
-  public String toString() {
-    return Objects.toStringHelper(this)
-        .add("file", file)
-        .add("position", position)
-        .add("count", count)
-        .toString();
-  }
-}