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.lucene.store; import java.io.EOFException; import java.io.IOException; import java.nio.ByteBuffer; import java.nio.channels.SeekableByteChannel; import java.nio.channels.ClosedChannelException; // javadoc @link import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.StandardOpenOption; import java.util.concurrent.Future; /** A straightforward implementation of {@link FSDirectory} * using {@link Files#newByteChannel(Path, java.nio.file.OpenOption...)}. * However, this class has * poor concurrent performance (multiple threads will * bottleneck) as it synchronizes when multiple threads * read from the same file. It's usually better to use * {@link NIOFSDirectory} or {@link MMapDirectory} instead. * <p> * <b>NOTE:</b> Accessing this class either directly or * indirectly from a thread while it's interrupted can close the * underlying file descriptor immediately if at the same time the thread is * blocked on IO. The file descriptor will remain closed and subsequent access * to {@link SimpleFSDirectory} will throw a {@link ClosedChannelException}. If * your application uses either {@link Thread#interrupt()} or * {@link Future#cancel(boolean)} you should use the legacy {@code RAFDirectory} * from the Lucene {@code misc} module in favor of {@link SimpleFSDirectory}. * </p> */ public class SimpleFSDirectory extends FSDirectory { /** Create a new SimpleFSDirectory for the named location. * The directory is created at the named location if it does not yet exist. * * @param path the path of the directory * @param lockFactory the lock factory to use * @throws IOException if there is a low-level I/O error */ public SimpleFSDirectory(Path path, LockFactory lockFactory) throws IOException { super(path, lockFactory); } /** Create a new SimpleFSDirectory for the named location and {@link FSLockFactory#getDefault()}. * The directory is created at the named location if it does not yet exist. * * @param path the path of the directory * @throws IOException if there is a low-level I/O error */ public SimpleFSDirectory(Path path) throws IOException { this(path, FSLockFactory.getDefault()); } /** Creates an IndexInput for the file with the given name. */ @Override public IndexInput openInput(String name, IOContext context) throws IOException { ensureOpen(); ensureCanRead(name); Path path = directory.resolve(name); SeekableByteChannel channel = Files.newByteChannel(path, StandardOpenOption.READ); return new SimpleFSIndexInput("SimpleFSIndexInput(path=\"" + path + "\")", channel, context); } /** * Reads bytes with {@link SeekableByteChannel#read(ByteBuffer)} */ static final class SimpleFSIndexInput extends BufferedIndexInput { /** * The maximum chunk size for reads of 16384 bytes. */ private static final int CHUNK_SIZE = 16384; /** the channel we will read from */ protected final SeekableByteChannel channel; /** is this instance a clone and hence does not own the file to close it */ boolean isClone = false; /** start offset: non-zero in the slice case */ protected final long off; /** end offset (start+length) */ protected final long end; private ByteBuffer byteBuf; // wraps the buffer for NIO public SimpleFSIndexInput(String resourceDesc, SeekableByteChannel channel, IOContext context) throws IOException { super(resourceDesc, context); this.channel = channel; this.off = 0L; this.end = channel.size(); } public SimpleFSIndexInput(String resourceDesc, SeekableByteChannel channel, long off, long length, int bufferSize) { super(resourceDesc, bufferSize); this.channel = channel; this.off = off; this.end = off + length; this.isClone = true; } @Override public void close() throws IOException { if (!isClone) { channel.close(); } } @Override public SimpleFSIndexInput clone() { SimpleFSIndexInput clone = (SimpleFSIndexInput) super.clone(); clone.isClone = true; return clone; } @Override public IndexInput slice(String sliceDescription, long offset, long length) throws IOException { if (offset < 0 || length < 0 || offset + length > this.length()) { throw new IllegalArgumentException("slice() " + sliceDescription + " out of bounds: offset=" + offset + ",length=" + length + ",fileLength=" + this.length() + ": " + this); } return new SimpleFSIndexInput(getFullSliceDescription(sliceDescription), channel, off + offset, length, getBufferSize()); } @Override public final long length() { return end - off; } @Override protected void newBuffer(byte[] newBuffer) { super.newBuffer(newBuffer); byteBuf = ByteBuffer.wrap(newBuffer); } @Override protected void readInternal(byte[] b, int offset, int len) throws IOException { final ByteBuffer bb; // Determine the ByteBuffer we should use if (b == buffer) { // Use our own pre-wrapped byteBuf: assert byteBuf != null; bb = byteBuf; byteBuf.clear().position(offset); } else { bb = ByteBuffer.wrap(b, offset, len); } synchronized (channel) { long pos = getFilePointer() + off; if (pos + len > end) { throw new EOFException("read past EOF: " + this); } try { channel.position(pos); int readLength = len; while (readLength > 0) { final int toRead = Math.min(CHUNK_SIZE, readLength); bb.limit(bb.position() + toRead); assert bb.remaining() == toRead; final int i = channel.read(bb); if (i < 0) { // be defensive here, even though we checked before hand, something could have changed throw new EOFException("read past EOF: " + this + " off: " + offset + " len: " + len + " pos: " + pos + " chunkLen: " + toRead + " end: " + end); } assert i > 0 : "SeekableByteChannel.read with non zero-length bb.remaining() must always read at least one byte (Channel is in blocking mode, see spec of ReadableByteChannel)"; pos += i; readLength -= i; } assert readLength == 0; } catch (IOException ioe) { throw new IOException(ioe.getMessage() + ": " + this, ioe); } } } @Override protected void seekInternal(long pos) throws IOException { if (pos > length()) { throw new EOFException("read past EOF: pos=" + pos + " vs length=" + length() + ": " + this); } } } }