On 19/07/2016 17:19, Berneburg, Cris J. - US wrote: <snip/>
>> This is probably a useful read: >> http://people.apache.org/~markt/presentations/2010-11-04-Memory-Leaks-60mins.pdf >> >> Despite the age, it is still very relevant today. > > > Thanks for reminding me about that document. It does sound relevant. The > document says, > >> How memory leaks occur: Reference chains >> [...] >> Retaining a reference to a single object from a web application >> pins every class loaded by the web application in the Permanent >> Generation > > Practically speaking, how is a reference retained? > 1. Is a module-level (member) variable in a Servlet an example? No. Assuming the class that defines the Servlet is packaged with the web application (i.e. in a JAR in WEB-INF/lib or in WEB-INF/classes > 2. How about using ServletContext.setAttribute without an accompanying > removeAttribute? No. > 3. I see in one of my listeners some member (module-level) variables: a > private static for the logger and also a protected final String. Is that a > problem? No. > If you could provide a little more guidance about the details, I would > appreciate it. Sure. There are two categories of objects we are concerned about. Objects defined by classes that are provided by your web application (in WEB-INF/lib or WEB-INF/classes) and objects defined by classes that are provided by the container (Tomcat) or the JVM. References from web application objects to web application objects are fine. References from web application objects to container objects are fine. References from container objects to web application objects are potentially a problem. Additionally, references from container objects to the web application class loader are potentially a problem. For example: When you start a thread in a web application, the thread context class loader will be the web application class loader and the thread holds a reference to this. If the thread is not stopped when the web application is stopped there will be a reference held to the web application class loader which will cause a leak. If you add a logging framework to Tomcat's lib directory and then package a custom log formatter with your web application, the formatter will be registered with the logging framework and unless you unregister it when the application stops there will be reference from logging framework to custom formatter object to custom formatter class to web application class loader which will cause a leak. HTH, Mark P.S. I'll be talking about this (hopefully - if my talk gets accepted) at ApacheCon EU later this year. --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@tomcat.apache.org For additional commands, e-mail: users-h...@tomcat.apache.org
