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.hadoop.hdfs.server.namenode; import java.io.DataOutputStream; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.RandomAccessFile; import java.nio.ByteBuffer; import java.nio.channels.FileChannel; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.hdfs.DFSConfigKeys; import org.apache.hadoop.hdfs.protocol.LayoutFlags; import org.apache.hadoop.io.IOUtils; import com.google.common.annotations.VisibleForTesting; /** * An implementation of the abstract class {@link EditLogOutputStream}, which * stores edits in a local file. */ @InterfaceAudience.Private public class EditLogFileOutputStream extends EditLogOutputStream { private static final Log LOG = LogFactory.getLog(EditLogFileOutputStream.class); public static final int MIN_PREALLOCATION_LENGTH = 1024 * 1024; private File file; private FileOutputStream fp; // file stream for storing edit logs private FileChannel fc; // channel of the file stream for sync private EditsDoubleBuffer doubleBuf; static final ByteBuffer fill = ByteBuffer.allocateDirect(MIN_PREALLOCATION_LENGTH); private boolean shouldSyncWritesAndSkipFsync = false; private static boolean shouldSkipFsyncForTests = false; static { fill.position(0); for (int i = 0; i < fill.capacity(); i++) { fill.put(FSEditLogOpCodes.OP_INVALID.getOpCode()); } } /** * Creates output buffers and file object. * * @param conf * Configuration object * @param name * File name to store edit log * @param size * Size of flush buffer * @throws IOException */ public EditLogFileOutputStream(Configuration conf, File name, int size) throws IOException { super(); shouldSyncWritesAndSkipFsync = conf.getBoolean(DFSConfigKeys.DFS_NAMENODE_EDITS_NOEDITLOGCHANNELFLUSH, DFSConfigKeys.DFS_NAMENODE_EDITS_NOEDITLOGCHANNELFLUSH_DEFAULT); file = name; doubleBuf = new EditsDoubleBuffer(size); RandomAccessFile rp; if (shouldSyncWritesAndSkipFsync) { rp = new RandomAccessFile(name, "rws"); } else { rp = new RandomAccessFile(name, "rw"); } fp = new FileOutputStream(rp.getFD()); // open for append fc = rp.getChannel(); fc.position(fc.size()); } @Override public void write(FSEditLogOp op) throws IOException { doubleBuf.writeOp(op); } /** * Write a transaction to the stream. The serialization format is: * <ul> * <li>the opcode (byte)</li> * <li>the transaction id (long)</li> * <li>the actual Writables for the transaction</li> * </ul> * */ @Override public void writeRaw(byte[] bytes, int offset, int length) throws IOException { doubleBuf.writeRaw(bytes, offset, length); } /** * Create empty edits logs file. */ @Override public void create(int layoutVersion) throws IOException { fc.truncate(0); fc.position(0); writeHeader(layoutVersion, doubleBuf.getCurrentBuf()); setReadyToFlush(); flush(); } /** * Write header information for this EditLogFileOutputStream to the provided * DataOutputSream. * * @param layoutVersion the LayoutVersion of the EditLog * @param out the output stream to write the header to. * @throws IOException in the event of error writing to the stream. */ @VisibleForTesting public static void writeHeader(int layoutVersion, DataOutputStream out) throws IOException { out.writeInt(layoutVersion); LayoutFlags.write(out); } @Override public void close() throws IOException { if (fp == null) { throw new IOException("Trying to use aborted output stream"); } try { // close should have been called after all pending transactions // have been flushed & synced. // if already closed, just skip if (doubleBuf != null) { doubleBuf.close(); doubleBuf = null; } // remove any preallocated padding bytes from the transaction log. if (fc != null && fc.isOpen()) { fc.truncate(fc.position()); fc.close(); fc = null; } fp.close(); fp = null; } finally { IOUtils.cleanup(LOG, fc, fp); doubleBuf = null; fc = null; fp = null; } fp = null; } @Override public void abort() throws IOException { if (fp == null) { return; } IOUtils.cleanup(LOG, fp); fp = null; } /** * All data that has been written to the stream so far will be flushed. New * data can be still written to the stream while flushing is performed. */ @Override public void setReadyToFlush() throws IOException { doubleBuf.setReadyToFlush(); } /** * Flush ready buffer to persistent store. currentBuffer is not flushed as it * accumulates new log records while readyBuffer will be flushed and synced. */ @Override public void flushAndSync(boolean durable) throws IOException { if (fp == null) { throw new IOException("Trying to use aborted output stream"); } if (doubleBuf.isFlushed()) { LOG.info("Nothing to flush"); return; } preallocate(); // preallocate file if necessary doubleBuf.flushTo(fp); if (durable && !shouldSkipFsyncForTests && !shouldSyncWritesAndSkipFsync) { fc.force(false); // metadata updates not needed } } /** * @return true if the number of buffered data exceeds the intial buffer size */ @Override public boolean shouldForceSync() { return doubleBuf.shouldForceSync(); } private void preallocate() throws IOException { long position = fc.position(); long size = fc.size(); int bufSize = doubleBuf.getReadyBuf().getLength(); long need = bufSize - (size - position); if (need <= 0) { return; } long oldSize = size; long total = 0; long fillCapacity = fill.capacity(); while (need > 0) { fill.position(0); IOUtils.writeFully(fc, fill, size); need -= fillCapacity; size += fillCapacity; total += fillCapacity; } if (LOG.isDebugEnabled()) { LOG.debug("Preallocated " + total + " bytes at the end of " + "the edit log (offset " + oldSize + ")"); } } /** * Returns the file associated with this stream. */ File getFile() { return file; } @Override public String toString() { return "EditLogFileOutputStream(" + file + ")"; } /** * @return true if this stream is currently open. */ public boolean isOpen() { return fp != null; } @VisibleForTesting public void setFileChannelForTesting(FileChannel fc) { this.fc = fc; } @VisibleForTesting public FileChannel getFileChannelForTesting() { return fc; } /** * For the purposes of unit tests, we don't need to actually * write durably to disk. So, we can skip the fsync() calls * for a speed improvement. * @param skip true if fsync should <em>not</em> be called */ @VisibleForTesting public static void setShouldSkipFsyncForTesting(boolean skip) { shouldSkipFsyncForTests = skip; } }