[jboss-user] [EJB3] - Re: Failed to acquire the pool semaphore in empty pool

[Garry Dias]

Garry Dias [https://community.jboss.org/people/garrydias] created the discussion

"Re: Failed to acquire the pool semaphore in empty pool"

To view the discussion, visit: https://community.jboss.org/message/760376#760376

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Yes. I´m still writing a post with a sequence diagram to explain better.

To be short:

At the line where I worte // A JMSConsumer is created to retrieve exchange object when MDB end there´s lot of statements and one of that is a call to javax.jms.MessageConsumer.receive() method. However, when the producer sent the message it set a Time To Live in my jms message. This TTL was 20 seconds. As my MDB connect to a third party webService that hangs more than 30 seconds sometimes, my jms message died before MDB acks the comsumption. Meanwhile, the javax.jms.MessageConsumer.receive() method is waiting for a message that should never come because the jms message relies in DLQ now. So, javax.jms.MessageConsumer.receive() method will wait forever and an available MyWorkerBean instance in my pool (annotated as @Pool(value = PoolDefaults.POOL_IMPLEMENTATION_STRICTMAX, maxSize = 30)) will be decreased. You can see this decreasing in jmx-console, menu j2ee.

The solution was set a TTL for MessageConsumer.receive() method. So today my code looks like this:

@Clustered
@Local(MyWorkerInterface.class)
@Stateless(name = "MyWorkerBean")
@Interceptors(value = { SpringBeanAutowiringInterceptor.class, LoggingInterceptor.class })
@RolesAllowed(value = "client")
@Pool(value = PoolDefaults.POOL_IMPLEMENTATION_STRICTMAX, maxSize = 30)
*public* *class* MyWorkerBean *implements* MyWorkerInterface {
 
    @RolesAllowed("client")
    @TransactionAttribute(TransactionAttributeType.NOT_SUPPORTED)
    *public* WorkResponse execute(*final* WorkRequest workRequest) {
 
        *long* start = System.currentTimeMillis();
 
        WorkExchange exchange = *new* WorkExchange();
        exchange.setWorkRequest(workRequest);
 
        // A JMSProducer is created to send exchange to a JMS queue
        // A MDB class retrieve data from a third party webservice (expensive operation taking between 300 to 60000ms to finish) using WorkExchange.workRequest fields
        ...
ObjectMessage responseMessage = (ObjectMessage) messageConsumer.receive(20000); 
        ... 

        LoggerUtil.info("Operation time: " + (System.currentTimeMillis() - start));
 
        // WorkExchange.workResponse have been set by MDB
        WorkResponse response = exhange.getWorkResponse();
 
        *return* response;
    }
}

[]s
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