Question

I’m currently having an issue with stopping a background thread in a webachive. I currently tie it in the war’s deployment, and destroy it when the archive is un-deployed.

The threads starts up without issue, but when I close the archive, It seems to lose the handle on the thread. In the below case: st is null when the contextDestroyed method is called.

This is an issue as Tomcat notes the thread as orphaned in its warning about memory leaks.

public class LimitOrderContextListener implements ServletContextListener {

    static Logger logger = Logger.getLogger(LimitOrderRuntime.class.getName());
    private SwiftThread st = null;

    /**
     * Initializes this listener when this war's context is initialized
     */
    public void contextInitialized(ServletContextEvent sce) 
    {
        try {
            if ( (st == null) || (!st.isAlive()) )  {
                LimitOrderRuntime lor = new LimitOrderRuntime();
                SwiftThread st = new SwiftThread(lor);
                st.start();
            } else {
                st.gracefulStop();
                st.join(2000);
            }
        } catch(Exception e)    {
            logger.warn("Unable to properly load thread! " + 
                    e.getMessage() + " --cause " + e.getCause());
            e.printStackTrace();
        }

    }

    /**
     * When this war is destroyed/stopped, stop the thread.
     */
    public void contextDestroyed(ServletContextEvent sce) 
    {
        try {
            boolean success = st.gracefulStop();
            if (!success)   {
                st.interrupt();
            }
        } catch (Exception e)   {
            logger.warn("Unable to properly release thread! " + 
                    e.getMessage() + " --cause " + e.getCause());
            e.printStackTrace();
        }    
    }

}

Answer 1

In your contextInitialized method, you’re redeclaring st as a local variable, rather than initializing the instance variable with the thread.

Replace

SwiftThread st = new SwiftThread(lor);

with

this.st = new SwiftThread(lor);