Fix ApplicationListeners being skipped

[phinner]

Basically, when a ApplicationListener uses Application#removeListener while the application is iterating over the listener seq, the next listener in the iteration is skipped.

This issue hasn't been noticed for so long since the only use of it is within the dispose of Timer.TimerThread, and that it runs before listeners that doesn't use dispose.

But in BE servers, it prevents my plugins from exiting since Timer is used early by BeControl, running before my plugin shutdown listener thus skipping it.

The fix is simply replacing the removed listener by an empty one.

[Anuken]

Isn't this kind of a memory leak? If you call add and remove in a loop, it will OOM eventually.

[phinner]

Isn't this kind of a memory leak? If you call add and remove in a loop, it will OOM eventually.

Well, my reasoning was since it is used rarely and also too much changes, it would do the trick, but now that you mention it... I'll get back to it.

[phinner]

Okay, if you don't mind making removeListener and addListener non default, what about this ?

public abstract class AbstractApplication implements Application{

    protected final Seq<ApplicationListener> listeners = new Seq<>();
    protected boolean runningListeners = false;
    protected final Seq<ApplicationListener> removing = new Seq<>();

    @Override
    public Seq<ApplicationListener> getListeners(){
        return listeners;
    }

    @Override
    public void addListener(ApplicationListener listener){
        synchronized(listeners){
            listeners.add(listener);
            removing.remove(listener);
        }
    }

    @Override
    public void removeListener(ApplicationListener listener){
        synchronized(listeners){
            if (runningListeners) removing.add(listener);
            else listeners.remove(listener);
        }
    }

    @Override
    public void forEachListener(Cons<ApplicationListener> cons){
        synchronized(listeners){
            runningListeners = true;
            try{
                for(ApplicationListener listener : listeners){
                    if(removing.contains(listener)) continue;
                    cons.get(listener);
                }
            }finally{
                runningListeners = false;
            }
            listeners.removeAll(removing);
            removing.clear();
        }
    }
}

The forEachListener makes sure no funny business occurs when one want to use the listeners.

[phinner]

Looks like I made things too complicated again, the solution was simply removing the listener when it's guaranteed the others are not used.