Wednesday, December 19, 2012

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;
        }
    };

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