Github user srowen commented on a diff in the pull request: https://github.com/apache/spark/pull/15408#discussion_r82556289 --- Diff: core/src/main/java/org/apache/spark/io/NioBasedBufferedFileInputStream.java --- @@ -0,0 +1,120 @@ +/* + * 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 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. + * + */ +public final class NioBasedBufferedFileInputStream extends InputStream { + + private static int DEFAULT_BUFFER_SIZE = 8192; + + private final ByteBuffer byteBuffer; + + private final FileChannel fileChannel; + + public NioBasedBufferedFileInputStream(File file, int bufferSize) throws IOException { + byteBuffer = ByteBuffer.allocateDirect(bufferSize); + fileChannel = FileChannel.open(file.toPath(), StandardOpenOption.READ); + byteBuffer.flip(); + } + + public NioBasedBufferedFileInputStream(File file) throws IOException { + this(file, DEFAULT_BUFFER_SIZE); + } + + private boolean refill() throws IOException { + if (!byteBuffer.hasRemaining()) { + byteBuffer.clear(); + int nRead = fileChannel.read(byteBuffer); + if (nRead == -1) { + return false; + } + byteBuffer.flip(); + } + return true; + } + + @Override + public int read() throws IOException { + if (!refill()) { + return -1; + } + return byteBuffer.get() & 0xFF; + } + + @Override + public int read(byte[] b, int off, int len) throws IOException { + if (!refill()) { + return -1; + } + len = Math.min(len, byteBuffer.remaining()); + byteBuffer.get(b, off, len); + return len; + } + + @Override + public int available() throws IOException { --- End diff -- It's a standard API method for `InputStream`, so if something does call it, it's better to return a useful answer because it's pretty easy to do so.
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