Question

I’m new to threads and am trying to replicate a simple example of interrupting a thread in my web app. I have the class below (ComputeResults has other variables and functions, setters/getters etc but this is the new code I can’t get to work):

@ManagedBean(name="results")
@RequestScoped
public class ComputeResults implements Serializable{

    Thread scan;
    public void testrun() {
    scan = new Thread(new Runnable() {
        @Override
        public void run() {
            int i = 0;
            while (!Thread.currentThread().isInterrupted()) {
                try {
                    i++;
                    if (i == 1) {
                        scan.interrupt();
                    }
                } 
                catch (Exception e) {
                    Thread.currentThread().interrupt();
                }
                catch (Throwable t) {
                    System.out.println("Thrown test: "+t.getMessage());
                }
            }
        }
    });

    scan.start();
}

    public void stoprun() {
        if(scan != null){
            scan.interrupt();
        }
    }
}

In my interface I have a button to start the thread:

<p:commandLink action="submit" value="" onclick="testdialog.show()" oncomplete="testdialog.hide()" actionListener="#{results.testrun}" update="messages, runmsg, @form results" />

and one to attempt to interrupt it:

<p:commandButton action="submit" value="Cancel Test" onclick="testdialog.hide()" actionListener="#{results.stoprun}" update="messages, runmsg" />

Problem is the ‘stoprun’ function sees ‘scan’ as null and I’m not sure why. Adding scan.interrupt() inside testrun() works fine. I thought about using Thread.currentThread().interrupt() but it seems that the current thread ID/name is different when I call stoprun.

Answer 1

That’s because the bean is @RequestScoped – each HTTP request (= button click) gets a new instance.

You need to make it @Scope("session") at least.