Java tutorial
/** * 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.tajo.pullserver; import com.google.common.annotations.VisibleForTesting; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.io.ReadaheadPool; import org.apache.hadoop.io.nativeio.NativeIO; import io.netty.channel.DefaultFileRegion; import java.io.FileDescriptor; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import java.nio.channels.WritableByteChannel; public class FadvisedFileRegion extends DefaultFileRegion { private static final Log LOG = LogFactory.getLog(FadvisedFileRegion.class); private final boolean manageOsCache; private final int readaheadLength; private final ReadaheadPool readaheadPool; private final FileDescriptor fd; private final String identifier; private final long count; private final long position; private final int shuffleBufferSize; private final boolean shuffleTransferToAllowed; private final FileChannel fileChannel; private ReadaheadPool.ReadaheadRequest readaheadRequest; public static final int DEFAULT_SHUFFLE_BUFFER_SIZE = 128 * 1024; public FadvisedFileRegion(RandomAccessFile file, long position, long count, boolean manageOsCache, int readaheadLength, ReadaheadPool readaheadPool, String identifier) throws IOException { this(file, position, count, manageOsCache, readaheadLength, readaheadPool, identifier, DEFAULT_SHUFFLE_BUFFER_SIZE, true); } public FadvisedFileRegion(RandomAccessFile file, long position, long count, boolean manageOsCache, int readaheadLength, ReadaheadPool readaheadPool, String identifier, int shuffleBufferSize, boolean shuffleTransferToAllowed) throws IOException { super(file.getChannel(), position, count); this.manageOsCache = manageOsCache; this.readaheadLength = readaheadLength; this.readaheadPool = readaheadPool; this.fd = file.getFD(); this.identifier = identifier; this.fileChannel = file.getChannel(); this.count = count; this.position = position; this.shuffleBufferSize = shuffleBufferSize; this.shuffleTransferToAllowed = shuffleTransferToAllowed; } @Override public long transferTo(WritableByteChannel target, long position) throws IOException { if (PullServerUtil.isNativeIOPossible() && manageOsCache && readaheadPool != null) { readaheadRequest = readaheadPool.readaheadStream(identifier, fd, position() + position, readaheadLength, position() + count(), readaheadRequest); } if (this.shuffleTransferToAllowed) { return super.transferTo(target, position); } else { return customShuffleTransfer(target, position); } } /** * This method transfers data using local buffer. It transfers data from * a disk to a local buffer in memory, and then it transfers data from the * buffer to the target. This is used only if transferTo is disallowed in * the configuration file. super.TransferTo does not perform well on Windows * due to a small IO request generated. customShuffleTransfer can control * the size of the IO requests by changing the size of the intermediate * buffer. */ @VisibleForTesting long customShuffleTransfer(WritableByteChannel target, long position) throws IOException { long actualCount = this.count - position; if (actualCount < 0 || position < 0) { throw new IllegalArgumentException( "position out of range: " + position + " (expected: 0 - " + (this.count - 1) + ')'); } if (actualCount == 0) { return 0L; } long trans = actualCount; int readSize; ByteBuffer byteBuffer = ByteBuffer.allocate(this.shuffleBufferSize); while (trans > 0L && (readSize = fileChannel.read(byteBuffer, this.position + position)) > 0) { //adjust counters and buffer limit if (readSize < trans) { trans -= readSize; position += readSize; byteBuffer.flip(); } else { //We can read more than we need if the actualCount is not multiple //of the byteBuffer size and file is big enough. In that case we cannot //use flip method but we need to set buffer limit manually to trans. byteBuffer.limit((int) trans); byteBuffer.position(0); position += trans; trans = 0; } //write data to the target while (byteBuffer.hasRemaining()) { target.write(byteBuffer); } byteBuffer.clear(); } return actualCount - trans; } @Override protected void deallocate() { if (readaheadRequest != null) { readaheadRequest.cancel(); readaheadRequest = null; } super.deallocate(); } /** * Call when the transfer completes successfully so we can advise the OS that * we don't need the region to be cached anymore. */ public void transferSuccessful() { if (PullServerUtil.isNativeIOPossible() && manageOsCache && count() > 0 && super.isOpen()) { try { PullServerUtil.posixFadviseIfPossible(identifier, fd, position(), count(), NativeIO.POSIX.POSIX_FADV_DONTNEED); } catch (Throwable t) { LOG.warn("Failed to manage OS cache for " + identifier, t); } } } }