[CAMEL-1510] BatchProcessor interrupt has side effects

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.6.0, 2.0-M1
• Fix Version/s: 1.6.1, 2.0-M2
• Component/s: camel-core

Environment

Mac OS X

• Patch Info: Patch Available
• Assignee: William Tam
• Reporter: Christopher Hunt
• Created: 02/Apr/09 01:05
• Updated: 21/Nov/09 11:57
• Resolved: 16/Apr/09 20:31

Description

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:

    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);
            }
        }
    }

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.