com.amazon.sqs.javamessaging

Class SQSMessageConsumerPrefetch

java.lang.Object

com.amazon.sqs.javamessaging.SQSMessageConsumerPrefetch

All Implemented Interfaces:

PrefetchManager, Runnable

public class SQSMessageConsumerPrefetch
extends Object
implements Runnable, PrefetchManager

Used internally to prefetch messages to internal buffer on a background thread for better receive turn around times.

Each message consumer creates one prefetch thread.

This runs until the message consumer is closed and in-progress SQS receiveMessage call returns.

Uses SQS receiveMessage with long-poll wait time of 20 seconds.

Add re-tries on top of AmazonSQSClient re-tries on SQS calls.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SQSMessageConsumerPrefetch.MessageManager

Field Summary

Fields

Modifier and Type	Field and Description
protected static String	ALL
protected ExponentialBackoffStrategy	backoffStrategy AWS SQS SDK with default backup strategy already re-tries 3 times exponentially.
protected boolean	closed States of the prefetch thread
protected ArrayDeque<SQSMessageConsumerPrefetch.MessageManager>	messageQueue Internal buffer of Messages.
protected int	messagesPrefetched Counter on how many messages are prefetched into internal messageQueue.
protected int	messagesRequested Counter on how many messages have been explicitly requested.
protected int	retriesAttempted Controls the number of retry attempts to the SQS
protected boolean	running
protected static int	WAIT_TIME_SECONDS

Method Summary

Modifier and Type	Method and Description
protected javax.jms.Message	convertToJMSMessage(com.amazonaws.services.sqs.model.Message message) Convert the return SQS message into JMS message
SQSMessageConsumer	getMessageConsumer() This is used to determine the state of the consumer, when the message listener scheduler is processing the messages.
protected List<com.amazonaws.services.sqs.model.Message>	getMessages(int batchSize, int waitTimeSeconds) Call receiveMessage with the given wait time.
protected List<com.amazonaws.services.sqs.model.Message>	getMessagesWithBackoff(int batchSize)
protected boolean	isClosed()
void	messageDispatched() Notify the prefetchThread that the message is dispatched from messageQueue when user calls for receive or message listener onMessage is called.
void	messageListenerReady() Notify the prefetchThread that the message listener has finished with any previous message and is ready to accept another.
protected void	nackQueueMessages()
protected void	notifyStateChange()
protected void	processReceivedMessages(List<com.amazonaws.services.sqs.model.Message> messages) Converts the received message to JMS message, and pushes to messages to either callback scheduler for asynchronous message delivery or to internal buffers for synchronous message delivery.
void	run() Runs until the message consumer is closed and in-progress SQS receiveMessage call returns.
protected void	setMessageListener(javax.jms.MessageListener messageListener) Sets the message listener.
protected void	sleep(long sleepTimeMillis) Sleeps for the configured time.
protected void	waitForPrefetch()
protected void	waitForStart()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

WAIT_TIME_SECONDS

protected static final int WAIT_TIME_SECONDS

See Also:

Constant Field Values

ALL

protected static final String ALL

See Also:

Constant Field Values

messageQueue

protected final ArrayDeque<SQSMessageConsumerPrefetch.MessageManager> messageQueue

Internal buffer of Messages. The size of queue is MIN_BATCH by default and it can be changed by user.

messagesPrefetched

protected int messagesPrefetched

Counter on how many messages are prefetched into internal messageQueue.

messagesRequested

protected int messagesRequested

Counter on how many messages have been explicitly requested. TODO: Consider renaming this class and several other variables now that this logic factors in message requests as well as prefetching.

closed

protected volatile boolean closed

States of the prefetch thread

running

protected volatile boolean running

retriesAttempted

protected int retriesAttempted

Controls the number of retry attempts to the SQS

backoffStrategy

protected ExponentialBackoffStrategy backoffStrategy

AWS SQS SDK with default backup strategy already re-tries 3 times exponentially. This backoff is on top of that to let the prefetch thread backoff after SDK completes re-tries with a max delay of 2 seconds and 25ms delayInterval.

Method Detail

getMessageConsumer

public SQSMessageConsumer getMessageConsumer()

Description copied from interface: PrefetchManager

This is used to determine the state of the consumer, when the message listener scheduler is processing the messages.

Specified by:

getMessageConsumer in interface PrefetchManager

Returns:

The message consumer, which owns the prefetchThread

setMessageListener

protected void setMessageListener(javax.jms.MessageListener messageListener)

Sets the message listener.

If message listener is set, the existing messages on the internal buffer will be pushed to session callback scheduler.

If message lister is set to null, then the messages on the internal buffer of session callback scheduler will be negative acknowledged, which will be handled by the session callback scheduler thread itself.

run

public void run()

Runs until the message consumer is closed and in-progress SQS receiveMessage call returns.

This blocks if configured number of prefetched messages are already received or connection has not started yet.

After consumer is closed, all the messages inside internal buffer will be negatively acknowledged.

Specified by:

run in interface Runnable

getMessages

protected List<com.amazonaws.services.sqs.model.Message> getMessages(int batchSize,
                                                                     int waitTimeSeconds)
                                                              throws javax.jms.JMSException

Call receiveMessage with the given wait time.

Throws:

javax.jms.JMSException

processReceivedMessages

protected void processReceivedMessages(List<com.amazonaws.services.sqs.model.Message> messages)

Converts the received message to JMS message, and pushes to messages to either callback scheduler for asynchronous message delivery or to internal buffers for synchronous message delivery. Messages that was not converted to JMS message will be immediately negative acknowledged.

getMessagesWithBackoff

protected List<com.amazonaws.services.sqs.model.Message> getMessagesWithBackoff(int batchSize)
                                                                         throws InterruptedException

Throws:

InterruptedException

waitForPrefetch

protected void waitForPrefetch()
                        throws InterruptedException

Throws:

InterruptedException

convertToJMSMessage

protected javax.jms.Message convertToJMSMessage(com.amazonaws.services.sqs.model.Message message)
                                         throws javax.jms.JMSException

Convert the return SQS message into JMS message

Parameters:

message - SQS message to convert

Returns:

Converted JMS message

Throws:

javax.jms.JMSException

nackQueueMessages

protected void nackQueueMessages()

waitForStart

protected void waitForStart()
                     throws InterruptedException

Throws:

InterruptedException

messageDispatched

public void messageDispatched()

Description copied from interface: PrefetchManager

Notify the prefetchThread that the message is dispatched from messageQueue when user calls for receive or message listener onMessage is called.

Specified by:

messageDispatched in interface PrefetchManager

messageListenerReady

public void messageListenerReady()

Description copied from interface: PrefetchManager

Notify the prefetchThread that the message listener has finished with any previous message and is ready to accept another.

Specified by:

messageListenerReady in interface PrefetchManager

notifyStateChange

protected void notifyStateChange()

sleep

protected void sleep(long sleepTimeMillis)
              throws InterruptedException

Sleeps for the configured time.

Throws:

InterruptedException

isClosed

protected boolean isClosed()