Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/15408#discussion_r83529504
--- Diff:
core/src/main/java/org/apache/spark/io/NioBufferedFileInputStream.java ---
@@ -0,0 +1,142 @@
+/*
+ * Licensed 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.io;
+
+import org.apache.spark.storage.StorageUtils;
+
+import javax.annotation.concurrent.ThreadSafe;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.file.StandardOpenOption;
+
+/**
+ * {@link InputStream} implementation which uses direct buffer
+ * to read a file to avoid extra copy of data between Java and
+ * native memory which happens when using {@link
java.io.BufferedInputStream}.
+ * Unfortunately, this is not something already available in JDK,
+ * {@link sun.nio.ch.ChannelInputStream} supports reading a file using nio,
+ * but does not support buffering.
+ *
+ * TODO: support {@link #mark(int)}/{@link #reset()}
+ *
+ */
+@ThreadSafe
+public final class NioBufferedFileInputStream extends InputStream {
+
+ private static int DEFAULT_BUFFER_SIZE_BYTES = 8192;
+
+ private final ByteBuffer byteBuffer;
+
+ private final FileChannel fileChannel;
+
+ public NioBufferedFileInputStream(File file, int bufferSizeInBytes)
throws IOException {
+ byteBuffer = ByteBuffer.allocateDirect(bufferSizeInBytes);
+ fileChannel = FileChannel.open(file.toPath(), StandardOpenOption.READ);
+ byteBuffer.flip();
+ }
+
+ public NioBufferedFileInputStream(File file) throws IOException {
+ this(file, DEFAULT_BUFFER_SIZE_BYTES);
+ }
+
+ /**
+ * Checks weather data is left to be read from the input stream.
+ * @return true if data is left, false otherwise
+ * @throws IOException
+ */
+ private boolean refill() throws IOException {
+ if (!byteBuffer.hasRemaining()) {
+ byteBuffer.clear();
+ int nRead = 0;
+ while (nRead == 0) {
+ nRead = fileChannel.read(byteBuffer);
+ }
+ if (nRead < 0) {
+ return false;
+ }
+ byteBuffer.flip();
+ }
+ return true;
+ }
+
+ @Override
+ public synchronized int read() throws IOException {
+ if (!refill()) {
+ return -1;
+ }
+ return byteBuffer.get() & 0xFF;
+ }
+
+ @Override
+ public synchronized int read(byte[] b, int offset, int len) throws
IOException {
+ if (offset < 0 || len < 0 || (offset + len) < 0 || (b.length - (offset
+ len)) < 0) {
--- End diff --
Hardly matters, but now that this condition has been made more explicit,
then final condition is simpler as `offset + len > b.length`
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