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This is the ehcache core module. Pair it with other modules for added functionality.
/**
* Copyright 2003-2010 Terracotta, Inc.
*
* 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 net.sf.ehcache.writer.writebehind;
import net.sf.ehcache.CacheEntry;
import net.sf.ehcache.CacheException;
import net.sf.ehcache.Element;
import net.sf.ehcache.config.CacheConfiguration;
import net.sf.ehcache.config.CacheWriterConfiguration;
import net.sf.ehcache.writer.CacheWriter;
import net.sf.ehcache.writer.writebehind.operations.DeleteOperation;
import net.sf.ehcache.writer.writebehind.operations.SingleOperation;
import net.sf.ehcache.writer.writebehind.operations.SingleOperationType;
import net.sf.ehcache.writer.writebehind.operations.WriteOperation;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* An implementation of write behind with a queue that is kept in non durable local heap.
*
* @author Geert Bevin
* @version $Id: WriteBehindQueue.java 3431 2011-01-10 09:54:32Z alexsnaps $
*/
class WriteBehindQueue {
private final static Logger LOGGER = Logger.getLogger(WriteBehindQueue.class.getName());
private static final int MS_IN_SEC = 1000;
private final String cacheName;
private final long minWriteDelayMs;
private final long maxWriteDelayMs;
private final int rateLimitPerSecond;
private final int maxQueueSize;
private final boolean writeBatching;
private final int writeBatchSize;
private final int retryAttempts;
private final int retryAttemptDelaySeconds;
private final Thread processingThread;
private final ReentrantReadWriteLock queueLock = new ReentrantReadWriteLock();
private final ReentrantReadWriteLock.ReadLock queueReadLock = queueLock.readLock();
private final ReentrantReadWriteLock.WriteLock queueWriteLock = queueLock.writeLock();
private final Condition queueIsFull = queueWriteLock.newCondition();
private final Condition queueIsEmpty = queueWriteLock.newCondition();
private final Condition queueIsStopped = queueWriteLock.newCondition();
private final AtomicLong lastProcessing = new AtomicLong(System.currentTimeMillis());
private final AtomicLong lastWorkDone = new AtomicLong(System.currentTimeMillis());
private final AtomicBoolean busyProcessing = new AtomicBoolean(false);
private volatile OperationsFilter filter;
private List waiting = new ArrayList();
private CacheWriter cacheWriter;
private boolean stopping;
private boolean stopped;
/**
* Create a new write behind queue.
*
* @param config the configuration for the queue
*/
public WriteBehindQueue(CacheConfiguration config) {
this.stopping = false;
this.stopped = true;
this.cacheName = config.getName();
// making a copy of the configuration locally to ensure that it will not be changed at runtime
final CacheWriterConfiguration cacheWriterConfig = config.getCacheWriterConfiguration();
this.minWriteDelayMs = cacheWriterConfig.getMinWriteDelay() * MS_IN_SEC;
this.maxWriteDelayMs = cacheWriterConfig.getMaxWriteDelay() * MS_IN_SEC;
this.rateLimitPerSecond = cacheWriterConfig.getRateLimitPerSecond();
this.maxQueueSize = cacheWriterConfig.getWriteBehindMaxQueueSize();
this.writeBatching = cacheWriterConfig.getWriteBatching();
this.writeBatchSize = cacheWriterConfig.getWriteBatchSize();
this.retryAttempts = cacheWriterConfig.getRetryAttempts();
this.retryAttemptDelaySeconds = cacheWriterConfig.getRetryAttemptDelaySeconds();
this.processingThread = new Thread(new ProcessingThread(), cacheName + " write-behind");
this.processingThread.setDaemon(true);
}
/**
* {@inheritDoc}
*/
public void start(CacheWriter writer) {
queueWriteLock.lock();
try {
if (!stopped) {
throw new CacheException("The write-behind queue for cache '" + cacheName + "' can't be started more than once");
}
if (processingThread.isAlive()) {
throw new CacheException("The thread with name " + processingThread.getName() + " already exists and is still running");
}
this.stopping = false;
this.stopped = false;
this.cacheWriter = writer;
processingThread.start();
} finally {
queueWriteLock.unlock();
}
}
/**
* {@inheritDoc}
*/
public void setOperationsFilter(OperationsFilter filter) {
this.filter = filter;
}
private long getLastProcessing() {
return lastProcessing.get();
}
/**
* Thread this will continuously process the items in the queue.
*/
private final class ProcessingThread implements Runnable {
public void run() {
try {
while (!isStopped()) {
processItems();
queueWriteLock.lock();
try {
// Wait for new items or until the min write delay has expired.
// Do not continue if the actual min write delay wasn't at least the one specified in the config
// otherwise it's possible to create a new work list for just a couple of items in case
// the item processor is very fast, causing a large amount of data churn.
// However, if the write delay is expired, the processing should start immediately.
try {
if (minWriteDelayMs != 0) {
long delay = minWriteDelayMs;
do {
queueIsEmpty.await(delay, TimeUnit.MILLISECONDS);
long actualDelay = System.currentTimeMillis() - getLastProcessing();
if (actualDelay < minWriteDelayMs) {
delay = minWriteDelayMs - actualDelay;
} else {
delay = 0;
}
} while (delay > 0);
} else {
while (!stopping && waiting.size() == 0) {
queueIsEmpty.await();
}
}
} catch (final InterruptedException e) {
// if the wait for items is interrupted, act as if the bucket was cancelled
stop();
Thread.currentThread().interrupt();
}
// If the queue is stopping and no more work is outstanding, perform the actual stop operation
if (stopping && waiting.isEmpty()) {
stopTheQueueThread();
}
queueIsFull.signal();
} finally {
queueWriteLock.unlock();
}
}
} finally {
stopTheQueueThread();
}
}
private void stopTheQueueThread() {
// Perform the actual stop operation and wake up everyone that is waiting for it.
queueWriteLock.lock();
try {
stopped = true;
stopping = false;
queueIsStopped.signalAll();
} finally {
queueWriteLock.unlock();
}
}
}
private void processItems() throws CacheException {
// ensure that the items aren't already being processed
if (busyProcessing.get()) {
throw new CacheException("The write behind queue for cache '" + cacheName + "' is already busy processing.");
}
// set some state related to this processing run
busyProcessing.set(true);
lastProcessing.set(System.currentTimeMillis());
try {
final int workSize;
final List quarantined;
queueWriteLock.lock();
try {
// quarantine local work
if (waiting.size() > 0) {
quarantined = waiting;
waiting = new ArrayList();
} else {
quarantined = null;
}
// check if work was quarantined
if (quarantined != null) {
workSize = quarantined.size();
} else {
workSize = 0;
}
} finally {
queueWriteLock.unlock();
}
// if there's no work that needs to be done, stop the processing
if (0 == workSize) {
if (LOGGER.isLoggable(Level.FINER)) {
LOGGER.finer(getThreadName() + " : processItems() : nothing to process");
}
return;
}
try {
filterQuarantined(quarantined);
// if the batching is enabled and work size is smaller than batch size, don't process anything as long as the
// max allowed delay hasn't expired
if (writeBatching && writeBatchSize > 0) {
// wait for another round if the batch size hasn't been filled up yet and the max write delay
// hasn't expired yet
if (workSize < writeBatchSize && maxWriteDelayMs > lastProcessing.get() - lastWorkDone.get()) {
waitUntilEnoughWorkItemsAvailable(quarantined, workSize);
return;
}
// enforce the rate limit and wait for another round if too much would be processed compared to
// the last time when a batch was executed
if (rateLimitPerSecond > 0) {
final long secondsSinceLastWorkDone = (System.currentTimeMillis() - lastWorkDone.get()) / MS_IN_SEC;
final long maxBatchSizeSinceLastWorkDone = rateLimitPerSecond * secondsSinceLastWorkDone;
final int batchSize = determineBatchSize(quarantined);
if (batchSize > maxBatchSizeSinceLastWorkDone) {
waitUntilEnoughTimeHasPassed(quarantined, batchSize, secondsSinceLastWorkDone);
return;
}
}
}
// set some state related to this processing run
lastWorkDone.set(System.currentTimeMillis());
if (LOGGER.isLoggable(Level.FINER)) {
LOGGER.finer(getThreadName() + " : processItems() : processing started");
}
// process the quarantined items and remove them as they're processed
processQuarantinedItems(quarantined);
} catch (final RuntimeException e) {
reassemble(quarantined);
throw e;
} catch (final Error e) {
reassemble(quarantined);
throw e;
}
} finally {
busyProcessing.set(false);
if (LOGGER.isLoggable(Level.FINER)) {
LOGGER.finer(getThreadName() + " : processItems() : processing finished");
}
}
}
private void waitUntilEnoughWorkItemsAvailable(List quarantined, int workSize) {
if (LOGGER.isLoggable(Level.FINER)) {
LOGGER.finer(getThreadName() + " : processItems() : only " + workSize + " work items available, waiting for "
+ writeBatchSize + " items to fill up a batch");
}
reassemble(quarantined);
}
private void waitUntilEnoughTimeHasPassed(List quarantined, int batchSize, long secondsSinceLastWorkDone) {
if (LOGGER.isLoggable(Level.FINER)) {
LOGGER.finer(getThreadName() + " : processItems() : last work was done " + secondsSinceLastWorkDone
+ " seconds ago, processing " + batchSize + " batch items would exceed the rate limit of "
+ rateLimitPerSecond + ", waiting for a while.");
}
reassemble(quarantined);
}
private int determineBatchSize(List quarantined) {
int batchSize = writeBatchSize;
if (quarantined.size() < batchSize) {
batchSize = quarantined.size();
}
return batchSize;
}
private void filterQuarantined(List quarantined) {
OperationsFilter operationsFilter = this.filter;
if (operationsFilter != null) {
operationsFilter.filter(quarantined, CastingOperationConverter.getInstance());
}
}
private void processQuarantinedItems(List quarantined) {
if (LOGGER.isLoggable(Level.CONFIG)) {
LOGGER.config(getThreadName() + " : processItems() : processing " + quarantined.size() + " quarantined items");
}
if (writeBatching && writeBatchSize > 0) {
processBatchedOperations(quarantined);
} else {
processSingleOperation(quarantined);
}
}
private void processBatchedOperations(List quarantined) {
final int batchSize = determineBatchSize(quarantined);
// create batches that are separated by operation type
final Map> separatedItemsPerType =
new TreeMap>();
for (int i = 0; i < batchSize; i++) {
final SingleOperation item = quarantined.get(i);
if (LOGGER.isLoggable(Level.CONFIG)) {
LOGGER.config(getThreadName() + " : processItems() : adding " + item + " to next batch");
}
List itemsPerType = separatedItemsPerType.get(item.getType());
if (null == itemsPerType) {
itemsPerType = new ArrayList();
separatedItemsPerType.put(item.getType(), itemsPerType);
}
itemsPerType.add(item);
}
// execute the batch operations
for (List itemsPerType : separatedItemsPerType.values()) {
int executionsLeft = retryAttempts + 1;
while (executionsLeft-- > 0) {
try {
itemsPerType.get(0).createBatchOperation(itemsPerType).performBatchOperation(cacheWriter);
break;
} catch (final RuntimeException e) {
if (executionsLeft <= 0) {
throw e;
} else {
LOGGER.warning("Exception while processing write behind queue, retrying in " + retryAttemptDelaySeconds
+ " seconds, " + executionsLeft + " retries left : " + e.getMessage());
try {
Thread.sleep(retryAttemptDelaySeconds * MS_IN_SEC);
} catch (InterruptedException e1) {
Thread.currentThread().interrupt();
throw e;
}
}
}
}
}
// remove the batched items
for (int i = 0; i < batchSize; i++) {
quarantined.remove(0);
}
if (!quarantined.isEmpty()) {
reassemble(quarantined);
}
}
private void processSingleOperation(List quarantined) {
while (!quarantined.isEmpty()) {
// process the next item
final SingleOperation item = quarantined.get(0);
if (LOGGER.isLoggable(Level.CONFIG)) {
LOGGER.config(getThreadName() + " : processItems() : processing " + item);
}
int executionsLeft = retryAttempts + 1;
while (executionsLeft-- > 0) {
try {
item.performSingleOperation(cacheWriter);
break;
} catch (final RuntimeException e) {
if (executionsLeft <= 0) {
throw e;
} else {
LOGGER.warning("Exception while processing write behind queue, retrying in " + retryAttemptDelaySeconds
+ " seconds, " + executionsLeft + " retries left : " + e.getMessage());
try {
Thread.sleep(retryAttemptDelaySeconds * MS_IN_SEC);
} catch (InterruptedException e1) {
Thread.currentThread().interrupt();
throw e;
}
}
}
}
quarantined.remove(0);
}
}
/**
* {@inheritDoc}
*/
public void write(Element element) {
queueWriteLock.lock();
waitForQueueSizeToDrop();
try {
if (stopping || stopped) {
throw new CacheException("The element '" + element + "' couldn't be added through the write-behind queue for cache '"
+ cacheName + "' since it's not started.");
}
waiting.add(new WriteOperation(element));
if (waiting.size() + 1 < maxQueueSize) {
queueIsFull.signal();
}
queueIsEmpty.signal();
} finally {
queueWriteLock.unlock();
}
}
private void waitForQueueSizeToDrop() {
if (maxQueueSize > 0) {
while (getQueueSize() >= maxQueueSize) {
try {
queueIsFull.await();
} catch (InterruptedException e) {
stop();
Thread.currentThread().interrupt();
}
}
}
}
/**
* {@inheritDoc}
*/
public void delete(CacheEntry entry) {
queueWriteLock.lock();
waitForQueueSizeToDrop();
try {
if (stopping || stopped) {
throw new CacheException("The entry for key '" + entry.getKey() + "' couldn't be deleted through the write-behind "
+ "queue for cache '" + cacheName + "' since it's not started.");
}
waiting.add(new DeleteOperation(entry));
if (waiting.size() + 1 < maxQueueSize) {
queueIsFull.signal();
}
queueIsEmpty.signal();
} finally {
queueWriteLock.unlock();
}
}
/**
* {@inheritDoc}
*/
public void stop() throws CacheException {
queueWriteLock.lock();
try {
if (stopped) {
return;
}
stopping = true;
queueIsEmpty.signal();
while (!stopped) {
queueIsStopped.await();
}
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
throw new CacheException(e);
} finally {
queueWriteLock.unlock();
}
}
/**
* Gets the best estimate for items in the queue still awaiting processing.
* Not including elements currently processed
* @return the amount of elements still awaiting processing.
*/
public long getQueueSize() {
return waiting.size();
}
private boolean isStopped() {
queueReadLock.lock();
try {
return stopped;
} finally {
queueReadLock.unlock();
}
}
private String getThreadName() {
return processingThread.getName();
}
private void reassemble(List quarantined) {
queueWriteLock.lock();
try {
if (null == quarantined) {
return;
}
quarantined.addAll(waiting);
waiting = quarantined;
queueIsEmpty.signal();
} finally {
queueWriteLock.unlock();
}
}
}