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https://issues.apache.org/activemq/browse/CAMEL-1510?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=51273#action_51273
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Christopher Hunt commented on CAMEL-1510:
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Hi Martin,
I just had a look at your changes to StreamResequencer and wonder if you need
to signal that a request has been delivered using a boolean as well as relying
on the condition variable. Perhaps you do not need to discriminate between a
timeout and whether a request is made, but I thought you should know that a
condition variable can wake up spuriously on some platforms i.e. non-timeout
and non-signal.
>From the Java 5 javadoc:
_When waiting upon a Condition, a "spurious wakeup" is permitted to occur, in
general, as a concession to the underlying platform semantics. This has little
practical impact on most application programs as a Condition should always be
waited upon in a loop, testing the state predicate that is being waited for. An
implementation is free to remove the possibility of spurious wakeups but it is
recommended that applications programmers always assume that they can occur and
so always wait in a loop._
'hope that this is useful to you.
Kind regards,
Christopher
> BatchProcessor interrupt has side effects
> -----------------------------------------
>
> Key: CAMEL-1510
> URL: https://issues.apache.org/activemq/browse/CAMEL-1510
> Project: Apache Camel
> Issue Type: Bug
> Components: camel-core
> Affects Versions: 1.6.0, 2.0-M1
> Environment: Mac OS X
> Reporter: Christopher Hunt
> Assignee: William Tam
> Priority: Critical
> Fix For: 2.0.0, 1.6.1
>
> Attachments: BatchProcessor-lockmin.java.20.diff,
> BatchProcessor.java.20.diff, camel-core-1.x.patch, camel-core-2.x.patch
>
>
> I have noticed that the BatchProcessor class uses the Thread class interrupt
> method to wake the run loop from sleeping within the enqueueExchange method.
> The unfortunate side effect of this is that if the run loop is in the middle
> of processing exchanges, and the processing involves something slow like
> establishing a JMS connection over SSL or queuing to an asynchronous
> processor, then the processing can become interrupted. The consequence of
> this side effect is that the batch sender thread rarely gets the opportunity
> to complete properly and exceptions regarding the interrupt are thrown.
> This all became apparent during some performance testing that resulted in
> continuously adding exchanges to the aggregator, the threshold becoming
> reached, and then trying to enqueue the aggregated result to a JMS queue.
> If my analysis of the BatchProcessor is correct then I would recommend finer
> grained concurrency controls being used instead of relying upon interrupting
> a thread. Perhaps something like the following (untested) re-write of the
> sender:
> {code}
> private class BatchSender extends Thread {
> private Queue<Exchange> queue;
> private boolean exchangeQueued = false;
> private Lock queueMutex = new ReentrantLock();
> private Condition queueCondition = queueMutex.newCondition();
> public BatchSender() {
> super("Batch Sender");
> this.queue = new LinkedList<Exchange>();
> }
> public void cancel() {
> interrupt();
> }
> private void drainQueueTo(Collection<Exchange> collection, int
> batchSize) {
> for (int i = 0; i < batchSize; ++i) {
> Exchange e = queue.poll();
> if (e != null) {
> collection.add(e);
> } else {
> break;
> }
> }
> }
> public void enqueueExchange(Exchange exchange) {
> queueMutex.lock();
> try {
> queue.add(exchange);
> exchangeQueued = true;
> queueCondition.signal();
> } finally {
> queueMutex.unlock();
> }
> }
> @Override
> public void run() {
> queueMutex.lock();
> try {
> do {
> try {
> if (!exchangeQueued) {
> queueCondition.await(batchTimeout,
> TimeUnit.MILLISECONDS);
> if (!exchangeQueued) {
> drainQueueTo(collection, batchSize);
> }
> }
> if (exchangeQueued) {
> exchangeQueued = false;
> queueMutex.unlock();
> try {
> while (isInBatchCompleted(queue.size())) {
> queueMutex.lock();
> try {
> drainQueueTo(collection, batchSize);
> } finally {
> queueMutex.unlock();
> }
> }
> if (!isOutBatchCompleted()) {
> continue;
> }
> } finally {
> queueMutex.lock();
> }
> }
> queueMutex.unlock();
> try {
> try {
> sendExchanges();
> } catch (Exception e) {
> getExceptionHandler().handleException(e);
> }
> } finally {
> queueMutex.lock();
> }
> } catch (InterruptedException e) {
> break;
> }
> } while (true);
> } finally {
> queueMutex.unlock();
> }
> }
> private void sendExchanges() throws Exception {
> Iterator<Exchange> iter = collection.iterator();
> while (iter.hasNext()) {
> Exchange exchange = iter.next();
> iter.remove();
> processExchange(exchange);
> }
> }
> }
> {code}
> I have replaced the concurrent queue with a regular linked list and mutexed
> its access. In addition any queuing of exchanges is noted. This should result
> in less locking.
> The main change though is that queuing an exchange does not interrupt the
> batch sender's current activity.
> I hope that this sample is useful.
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