/**
* Starts the consumer which will register a queue or topic listener with Hazelcast and enable
* message consumption (push or pull). If the consumer is already active, this method does
* nothing.
*/
void start() {
if (active) {
return;
}
receiveLock.lock();
try {
// Start listening for events. We currently always listen for events even
// if we don't have a message listener. If this has a performance impact
// on Hazelcast we may want to only listen if there is a registered
// message listener that we need to notify.
IQueue<byte[]> queue = hazelcastMQContext.resolveQueue(destination);
if (queue != null) {
// Get the raw queue outside of any transactional context so we can add
// an item listener.
queue = config.getHazelcastInstance().getQueue(queue.getName());
queueListener = new HzQueueListener(queue);
}
// If we are a consumer on a topic, immediately start listening for events
// so we can buffer them for (a)synchronous consumption.
ITopic<byte[]> topic = hazelcastMQContext.resolveTopic(destination);
if (topic != null) {
topicListener = new HzTopicListener(topic);
}
active = true;
if (messageListener != null) {
// We have a message listener, so tell the context to drain the dispatch
// ready queues.
hazelcastMQContext.onConsumerDispatchReady(id);
} else {
// Signal that any receive requests can continue.
receiveCondition.signalAll();
}
} finally {
receiveLock.unlock();
}
}
/**
* Attempts to receive a message using the given strategy. The method will continue to attempt to
* receive until either {@link ReceiveStrategy#isRetryable()} returns false, a message is
* received, or the consumer is stopped.
*
* @param strategy the strategy to use for receiving the message and determining retries
* @return the message or null if no message was received
*/
private HazelcastMQMessage doReceive(ReceiveStrategy strategy) {
HazelcastMQMessage msg = null;
do {
receiveLock.lock();
try {
IQueue<byte[]> queue = hazelcastMQContext.resolveQueue(destination);
if (queue == null && topicListener == null) {
throw new HazelcastMQException(
format("Destination cannot be resolved [%s].", destination));
} else if (queue == null) {
queue = topicListener.getQueue();
}
byte[] msgData = strategy.receive(queue);
if (msgData != null) {
msg = config.getMessageConverter().toMessage(msgData);
}
// Check for message expiration if we have a message with expiration
// time.
if (msg != null && msg.getHeaders().get(Headers.EXPIRATION) != null) {
long expirationTime = Long.parseLong(msg.getHeaders().get(Headers.EXPIRATION));
if (expirationTime != 0 && expirationTime <= System.currentTimeMillis()) {
log.info("Dropping message [{}] because it has expired.", msg.getId());
msg = null;
}
}
} finally {
receiveLock.unlock();
}
} while (msg == null && !closed && strategy.isRetryable());
return msg;
}