io.joshworks.snappy.loader.data.RandomAccessDataFile Maven / Gradle / Ivy
/*
* Copyright 2012-2016 the original author or authors.
*
* 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 io.joshworks.snappy.loader.data;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.Semaphore;
/**
* {@link RandomAccessData} implementation backed by a {@link RandomAccessFile}.
*
* @author Phillip Webb
*/
public class RandomAccessDataFile implements RandomAccessData {
private static final int DEFAULT_CONCURRENT_READS = 4;
private final File file;
private final FilePool filePool;
private final long offset;
private final long length;
/**
* Create a new {@link RandomAccessDataFile} backed by the specified file.
*
* @param file the underlying file
* @throws IllegalArgumentException if the file is null or does not exist
* @see #RandomAccessDataFile(File, int)
*/
public RandomAccessDataFile(File file) {
this(file, DEFAULT_CONCURRENT_READS);
}
/**
* Create a new {@link RandomAccessDataFile} backed by the specified file.
*
* @param file the underlying file
* @param concurrentReads the maximum number of concurrent reads allowed on the
* underlying file before blocking
* @throws IllegalArgumentException if the file is null or does not exist
* @see #RandomAccessDataFile(File)
*/
public RandomAccessDataFile(File file, int concurrentReads) {
if (file == null) {
throw new IllegalArgumentException("File must not be null");
}
if (!file.exists()) {
throw new IllegalArgumentException("File must exist");
}
this.file = file;
this.filePool = new FilePool(concurrentReads);
this.offset = 0L;
this.length = file.length();
}
/**
* Private constructor used to create a {@link #getSubsection(long, long) subsection}.
*
* @param file the underlying file
* @param pool the underlying pool
* @param offset the offset of the section
* @param length the length of the section
*/
private RandomAccessDataFile(File file, FilePool pool, long offset, long length) {
this.file = file;
this.filePool = pool;
this.offset = offset;
this.length = length;
}
/**
* Returns the underlying File.
*
* @return the underlying file
*/
public File getFile() {
return this.file;
}
@Override
public InputStream getInputStream(ResourceAccess access) throws IOException {
return new DataInputStream(access);
}
@Override
public RandomAccessData getSubsection(long offset, long length) {
if (offset < 0 || length < 0 || offset + length > this.length) {
throw new IndexOutOfBoundsException();
}
return new RandomAccessDataFile(this.file, this.filePool, this.offset + offset,
length);
}
@Override
public long getSize() {
return this.length;
}
public void close() throws IOException {
this.filePool.close();
}
/**
* {@link RandomAccessDataInputStream} implementation for the
* {@link RandomAccessDataFile}.
*/
private class DataInputStream extends InputStream {
private RandomAccessFile file;
private int position;
DataInputStream(ResourceAccess access) throws IOException {
if (access == ResourceAccess.ONCE) {
this.file = new RandomAccessFile(RandomAccessDataFile.this.file, "r");
this.file.seek(RandomAccessDataFile.this.offset);
}
}
@Override
public int read() throws IOException {
return doRead(null, 0, 1);
}
@Override
public int read(byte[] b) throws IOException {
return read(b, 0, b == null ? 0 : b.length);
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException("Bytes must not be null");
}
return doRead(b, off, len);
}
/**
* Perform the actual read.
*
* @param b the bytes to read or {@code null} when reading a single byte
* @param off the offset of the byte array
* @param len the length of data to read
* @return the number of bytes read into {@code b} or the actual read byte if
* {@code b} is {@code null}. Returns -1 when the end of the stream is reached
* @throws IOException in case of I/O errors
*/
public int doRead(byte[] b, int off, int len) throws IOException {
if (len == 0) {
return 0;
}
int cappedLen = cap(len);
if (cappedLen <= 0) {
return -1;
}
RandomAccessFile file = this.file;
if (file == null) {
file = RandomAccessDataFile.this.filePool.acquire();
file.seek(RandomAccessDataFile.this.offset + this.position);
}
try {
if (b == null) {
int rtn = file.read();
moveOn(rtn == -1 ? 0 : 1);
return rtn;
} else {
return (int) moveOn(file.read(b, off, cappedLen));
}
} finally {
if (this.file == null) {
RandomAccessDataFile.this.filePool.release(file);
}
}
}
@Override
public long skip(long n) throws IOException {
return (n <= 0 ? 0 : moveOn(cap(n)));
}
@Override
public void close() throws IOException {
if (this.file != null) {
this.file.close();
}
}
/**
* Cap the specified value such that it cannot exceed the number of bytes
* remaining.
*
* @param n the value to cap
* @return the capped value
*/
private int cap(long n) {
return (int) Math.min(RandomAccessDataFile.this.length - this.position, n);
}
/**
* Move the stream position forwards the specified amount.
*
* @param amount the amount to move
* @return the amount moved
*/
private long moveOn(int amount) {
this.position += amount;
return amount;
}
}
/**
* Manage a pool that can be used to perform concurrent reads on the underlying
* {@link RandomAccessFile}.
*/
private class FilePool {
private final int size;
private final Semaphore available;
private final Queue files;
FilePool(int size) {
this.size = size;
this.available = new Semaphore(size);
this.files = new ConcurrentLinkedQueue();
}
public RandomAccessFile acquire() throws IOException {
this.available.acquireUninterruptibly();
RandomAccessFile file = this.files.poll();
if (file != null) {
return file;
}
return new RandomAccessFile(RandomAccessDataFile.this.file, "r");
}
public void release(RandomAccessFile file) {
this.files.add(file);
this.available.release();
}
public void close() throws IOException {
this.available.acquireUninterruptibly(this.size);
try {
RandomAccessFile file = this.files.poll();
while (file != null) {
file.close();
file = this.files.poll();
}
} finally {
this.available.release(this.size);
}
}
}
}
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