Package com.amazon.sqs.javamessaging

Class 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.

    • Field Detail

      • WAIT_TIME_SECONDS

        protected static int WAIT_TIME_SECONDS

      • 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.

      • 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()

      • 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()

      • isClosed

        protected boolean isClosed()