Skip to main content

CGlib enhancer and finalize method

Yesterday was a bad day because one of the node after updating to tomcat7 ran into full garbage collection. I took a heap dump and finally found that one of the enhanced class had 300K references hanging around in finalizer thread. I was  enhancing SimpelJDBCTemplate to find out time taken by each query and log it. The reason this happened because CGLib also enhanced the finalize method and in the method interceptor I was  delegating the call to the delegate object which was not existing at that time. Anyways the solution was to skip the enhancing of finalize by adding a callback filter and nooping on it.

As you can see in below code the filter returns 0 if finalize method is called and that means use the callback at 0th position in the callbacks which is a NoOp callback and for all others it uses 1st position which is my real code. 

The simple code fix was

    public static SimpleJdbcTemplate createPerfInterceptedTemplate(Class callerClass, DataSource dataSource) {
        final SimpleJdbcTemplate simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
        final String className = callerClass.getSimpleName();
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(SimpleJdbcTemplate.class);
        enhancer.setCallbackFilter(FINALIZE_FILTER);
        enhancer.setCallbacks(new Callback[]{NoOp.INSTANCE, new MethodInterceptor() {
            @Override
            public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
                ..........do your real delegate code here..........               
            }       
        }
}


private static final CallbackFilter FINALIZE_FILTER = new CallbackFilter() {
        public int accept(Method method) {
            if (method.getName().equals("finalize") &&
                method.getParameterTypes().length == 0 &&
                method.getReturnType() == Void.TYPE) {
                return 0;
            }
            return 1;
        }
    };

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()