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Judul : Threadlocal Retentiveness Leak Inwards Coffee Spider Web Application - Tomcat
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Threadlocal Retentiveness Leak Inwards Coffee Spider Web Application - Tomcat

ThreadLocal variables are infamous for creating retentivity leaks. Influenza A virus subtype H5N1 retentivity leak inward Java is total of retentivity gibe yesteryear object which are non inward role in addition to should accept been garbage collected, merely because of unintended potent references, they all the same alive in Java heap space. There are many ways retentivity leak tin live on caused inward Java merely when this retentivity leak is caused due to ThreadLocal variable, it’s refereed equally ThreadLocal retentivity leak. In our finally postal service nigh ThreadLocal variable, nosotros accept seen How ThreadLocal variable tin brand SimpleDateFormat thread-safe in addition to likewise raised signal that inward managed surroundings similar J2EE application server or spider web server similar Tomcat, Jetty, WebSphere or Weblogic role of ThreadLocal should live on avoided. In this postal service nosotros volition larn footling deep in addition to discovery out How ThreadLocal variables creates retentivity leak inward Java spider web application, much similar nosotros accept seen How to laid upward PermGen retentivity leak inward Tomcat. If you lot are non familiar amongst ThreadLocal variables I advise to larn through my previous post. Before going into especial let's recap How ThreadLocal bird industrial plant inward Java.

How ThreadLocal industrial plant inward Java :

thread-safe. ThreadLocal variables are stored inward a special map called ThreadLocalMap which is designed to gibe thread local objects, it uses WeakReferences for keys. 

Since every Thread has potent reference to in that place re-create of ThreadLocal variables, they are non garbage collected until Thread is Alive in addition to this is what creates retentivity leak inward a typical J2EE spider web application. This is explained inward especial inward adjacent department “How ThreadLocal variable creates retentivity leak inward Java”.

How ThreadLocal creates retentivity leak inward Java

In web server in addition to application server similar Tomcat or WebLogic, web-app is loaded yesteryear a different ClassLoader than which is used yesteryear Server itself. This ClassLoader loads in addition to unloads classes from spider web application. Web servers likewise maintains ThreadPool, which is collection of worker thread, to server HTTP requests. Now if 1 of the Servlet or whatever other Java bird from spider web application creates a ThreadLocal variable during asking processing in addition to doesn't take away it afterwards that, re-create of that Object volition remain amongst worker Thread in addition to since life-span of worker Thread is to a greater extent than than spider web app itself, it volition forestall the object in addition to ClassLoader, which uploaded the spider web app, from existence garbage collected. This volition create a retentivity leak inward Server. Now if you lot create this span of fourth dimension you lot may meet java.lang.OutOfMemoryError: PermGen space . Now this brings an of import question,  is it possible to to role ThreadLocal variable safely inward a managed environment?  Answer is Yes,, merely that requires a careful usage of ThreadLocal variable in addition to making certain to take away the object from ThreadLocal 1 time done.

How to role ThreadLocal safely inward Java Web application

Many people role Filters to initialize in addition to take away ThreadLocal variables. You tin initialize ThreadLocal inward filter, set to a greater extent than or less expensive object equally ThreadLocal in addition to 1 time asking has been processed take away it from ThreadLocal equally shown inward below example:

public void doFilter(ServeletRequest request, ServletResponse){
        try{

          //set ThreadLocal variable
        chain.doFilter(request, response)

        }finally{
          //remove threadLocal variable.
        }
}

That’s all on How ThreadLocal variable creates retentivity leak inward Java. Having said that, If non necessary or You tin create out without ThreadLocal variable than it’s best to avoid using ThreadLocal inward managed environments similar J2EE spider web in addition to application servers.

Further Learning
Java Memory Management
Understanding the Java Virtual Machine: Class Loading in addition to Reflection
Java Performance The Definitive Guide

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