Skip to main content

AtomicInteger

Found this interesting class AtomicInteger that allows you to access primitives in a highly concurrent environment. I ran into an issue when I had to implement a throttling filter to allow only certain no of request in the app for a particular functionality to guarantee a certain level of QOS, my earlier code was

public class BackupThrottlingFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            activeBackupRequests ++;
            if(activeBackupRequests > 50) {
                BackupFileUploadServlet.sendServiceUnavailableResponse((HttpServletResponse) response);
                return;
            }
            chain.doFilter(request, response);
        }
        finally {
            activeBackupRequests--;
        }
    }
    private static int activeBackupRequests;
}

Ran into an issue with this as its not synchronized so I had an option to use volatile or synchronized ,but synchronized is a killer as it would block but then I read about the new AtomicInteger class that allows you to abstract all this and allow highly concurrent operations on primitives


public class BackupThrottlingFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        try {
            activeBackupRequests.incrementAndGet();
            if (activeBackupRequests.get() > 50) {
                BackupFileUploadServlet.sendServiceUnavailableResponse((HttpServletResponse) response);
                return;
            }
            chain.doFilter(request, response);
        } finally {
            activeBackupRequests.decrementAndGet();
        }
    }
    private static AtomicInteger activeBackupRequests = new AtomicInteger(0);
}

Comments

Popular posts from this blog

RabbitMQ java clients for beginners

Here is a sample of a consumer and producer example for RabbitMQ. The steps are
Download ErlangDownload Rabbit MQ ServerDownload Rabbit MQ Java client jarsCompile and run the below two class and you are done.
This sample create a Durable Exchange, Queue and a Message. You will have to start the consumer first before you start the for the first time.

For more information on AMQP, Exchanges, Queues, read this excellent tutorial
http://blogs.digitar.com/jjww/2009/01/rabbits-and-warrens/

+++++++++++++++++RabbitMQProducer.java+++++++++++++++++++++++++++
import com.rabbitmq.client.Connection; import com.rabbitmq.client.Channel; import com.rabbitmq.client.*; public class RabbitMQProducer { public static void main(String []args) throws Exception { ConnectionFactory factory = new ConnectionFactory(); factory.setUsername("guest"); factory.setPassword("guest"); factory.setVirtualHost("/"); factory.setHost("127.0.0.1"); factory.setPort(5672); Conne…

Spring query timeout or transaction timeout

If you are using spring to manage transactions then you can specify default transaction timeout using

    <bean id="transactionManager"
        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource" />
        <property name="defaultTimeout" value="30" /> <!--30 sec--->             
    </bean>

or you can override the timeout in the annotation

    @Transactional(readOnly = false, timeout=30)


or if you are doing it programatic transactions then you can do


DataSourceTransactionManager transactionManager = new DataSourceTransactionManager(dataSource);
transactionManager.setDefaultTimeout(30);

 or you can override the timeout for one particular transaction

TransactionTemplate transactionTemplate = new TransactionTemplate();
transactionTemplate.setTimeout(30);

Python adding pid file

I have a thumbnail generator that launches multiple processes and the correct way to shut it down is to send kill -HUP to the parent process. To automate I had to write a pid file from python, it was a piece of cake
def writePidFile(): pid = str(os.getpid()) f = open('thumbnail_rabbit_consumer.pid', 'w') f.write(pid) f.close()