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/*
* * Copyright (c) 2004-2019 MarkLogic Corporation
* *
* * 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.
* *
* * The use of the Apache License does not indicate that this project is
* * affiliated with the Apache Software Foundation.
* *
* * Code adapted from Bixio DiskQueue
* * https://github.com/bixo/bixo/blob/master/src/main/java/bixo/utils/DiskQueue.java
* * Original work Copyright 2009-2015 Scale Unlimited
* * Modifications copyright (c) 2016 MarkLogic Corporation
*
*/
package com.marklogic.developer.corb;
import com.marklogic.developer.corb.util.IOUtils;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Serializable;
import java.security.InvalidParameterException;
import java.text.MessageFormat;
import java.util.AbstractQueue;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.marklogic.developer.corb.util.StringUtils;
/**
* A queue that writes extra elements to disk, and reads them in as needed.
*
* This implementation is optimized for being filled once (ie by the iterator in
* a reducer) and then incrementally read. So it wouldn't work very well if
* reads/writes were happening simultaneously, once anything had spilled to
* disk.
*
* @param
*/
public class DiskQueue extends AbstractQueue {
private static final Logger LOG = Logger.getLogger(DiskQueue.class.getName());
public static final float DEFAULT_REFILL_RATIO = 0.75f;
// The memoryQueue represents the head of the queue. It can also be the tail,
// if nothing has spilled over onto the disk.
private MemoryQueue memoryQueue;
// Percentage of memory queue used/capacity that triggers a refill from disk.
private float refillMemoryRatio;
// Number of elements in the backing store file on disk.
private int fileElementCount;
private File tempDir;
private BufferedWriter fileOut;
private BufferedReader fileIn;
// When moving elements from disk to memory, we don't know whether the memory
// queue has space until the offer is rejected. So rather than trying to push
// back an element into the file, just cache it in cachedElement.
private String cachedElement;
private File fileQueue;
/**
* Construct a disk-backed queue that keeps at most
* {@code maxInMemorySize} elements in memory.
*
* @param maxInMemorySize Maximum number of elements to keep in memory.
*/
public DiskQueue(int maxInMemorySize) {
this(maxInMemorySize, null);
}
/**
* Construct a disk-backed queue that keeps at most
* {@code maxInMemorySize} elements in memory.
*
* @param maxInMemorySize Maximum number of elements to keep in memory.
* @param tempDir Directory where queue temporary files will be written to.
*/
public DiskQueue(int maxInMemorySize, File tempDir) {
super();
if (maxInMemorySize < 1) {
throw new InvalidParameterException(DiskQueue.class.getSimpleName() + " max in-memory size must be at least one");
}
if (tempDir != null && !(tempDir.exists() && tempDir.isDirectory() && tempDir.canWrite())) {
throw new InvalidParameterException(DiskQueue.class.getSimpleName() + " temporary directory must exist and be writable");
}
this.tempDir = tempDir;
memoryQueue = new MemoryQueue<>(maxInMemorySize);
refillMemoryRatio = DEFAULT_REFILL_RATIO;
}
/* (non-Javadoc)
* @see java.lang.Object#finalize()
*
* Close down streams, and toss the temp file.
*/
@Override
protected void finalize() throws Throwable {
if (closeFile()) {
LOG.log(Level.WARNING, () -> MessageFormat.format("{0} still had open file in finalize", DiskQueue.class.getSimpleName()));
}
super.finalize();
}
/**
* Make sure the file streams are all closed down, the temp file is closed,
* and the temp file has been deleted.
*
* @return true if we had to close down the file.
*/
private boolean closeFile() {
if (fileQueue == null) {
return false;
}
IOUtils.closeQuietly(fileIn);
fileIn = null;
cachedElement = null;
IOUtils.closeQuietly(fileOut);
fileOut = null;
fileElementCount = 0;
fileQueue.delete();
fileQueue = null;
return true;
}
private void openFile() throws IOException {
if (fileQueue == null) {
fileQueue = File.createTempFile(DiskQueue.class.getSimpleName() + "-backingstore-", null, tempDir);
fileQueue.deleteOnExit();
LOG.log(Level.INFO, () -> MessageFormat.format("created backing store {0}", fileQueue.getAbsolutePath()));
fileOut = new BufferedWriter(new FileWriter(fileQueue));
// Flush output file, so there's something written when we open the input stream.
fileOut.flush();
fileIn = new BufferedReader(new FileReader(fileQueue));
}
}
@Override
public Iterator iterator() {
throw new UnsupportedOperationException(MessageFormat.format("Iterator is not supported for {0}", DiskQueue.class.getSimpleName()));
}
@Override
public int size() {
return memoryQueue.size() + fileElementCount + (cachedElement != null ? 1 : 0);
}
@Override
public boolean offer(String element) {
if (element == null) {
throw new NullPointerException("Element cannot be null for AbstractQueue");
}
// If there's anything in the file, or the queue is full, then we have to write to the file.
if (fileQueue != null || !memoryQueue.offer(element)) {
try {
openFile();
fileOut.write(element);
fileOut.newLine();
fileElementCount += 1;
} catch (IOException e) {
LOG.log(Level.SEVERE, MessageFormat.format("Error writing to {0} backing store {1}", DiskQueue.class.getSimpleName(), fileQueue.getAbsolutePath()), e);
return false;
}
}
return true;
}
@Override
public String peek() {
loadMemoryQueue();
return memoryQueue.peek();
}
@Override
public String remove() {
loadMemoryQueue();
return memoryQueue.remove();
}
@Override
public String poll() {
loadMemoryQueue();
return memoryQueue.poll();
}
/* (non-Javadoc)
* @see java.util.AbstractQueue#clear()
*
* Implement faster clear (so AbstractQueue doesn't call poll() repeatedly)
*/
@Override
public void clear() {
memoryQueue.clear();
cachedElement = null;
closeFile();
}
private void loadMemoryQueue() {
// use the memory queue as our buffer, so only load it up when it's below capacity.
if (memoryQueue.size() / (float) memoryQueue.getCapacity() >= refillMemoryRatio) {
return;
}
// See if we have one saved element from the previous read request
if (cachedElement != null && memoryQueue.offer(cachedElement)) {
cachedElement = null;
}
// Now see if we have anything on disk
if (fileQueue != null) {
try {
// Since we buffer writes, we need to make sure everything has
// been written before we start reading.
fileOut.flush();
while (fileElementCount > 0) {
@SuppressWarnings("unchecked")
String nextFileElement = fileIn.readLine();
fileElementCount -= 1;
if (!StringUtils.isEmpty(nextFileElement) && !memoryQueue.offer(nextFileElement)) {
//memory queue is full. Cache this entry and jump out
cachedElement = nextFileElement;
return;
}
}
// Nothing left in the file, so close/delete it.
closeFile();
// file queue is empty, so could reset length of file, read/write offsets
// to start from zero instead of closing file (but for current use case of fill once, drain
// once this works just fine)
} catch (IOException e) {
LOG.log(Level.SEVERE, MessageFormat.format("Error reading from {0} backing store", DiskQueue.class.getSimpleName()), e);
}
}
}
private static class MemoryQueue extends AbstractQueue {
private final List queue;
private final int capacity;
public MemoryQueue(int capacity) {
super();
this.capacity = capacity;
queue = new ArrayList<>(capacity);
}
@Override
public Iterator iterator() {
return queue.iterator();
}
public int getCapacity() {
return capacity;
}
@Override
public int size() {
return queue.size();
}
@Override
public boolean offer(String o) {
if (o == null) {
throw new NullPointerException();
} else if (queue.size() >= capacity) {
return false;
} else {
queue.add(o);
return true;
}
}
@Override
public String peek() {
if (queue.isEmpty()) {
return null;
} else {
return queue.get(0);
}
}
@Override
public String poll() {
if (queue.isEmpty()) {
return null;
} else {
return queue.remove(0);
}
}
@Override
public String remove() {
return queue.remove(0);
}
}
}
