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From: Steven Simpson <ss@domain.invalid>
Newsgroups: comp.lang.java.programmer
Subject: Re: Lightweight postDelayed / removeCallbacks
Date: Sun, 05 Feb 2012 22:00:50 +0000
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On 04/02/12 19:44, Jan Burse wrote:
>    postDelayed(Runnable r, int d):
>         Posts an event on the EDT, which will
>         invoked r after a delay of d millisecond.
>
>    removeCallbacks(Runnable r):
>         Immediately remove all events from the
>         EDT that would invoke r.
>
> One could use javax.swing.Timer for the first
> method. Something along:
>
>     public void postDelayed(final Runnable r, int d) {
>         final Timer t=new Timer(d,new ActionListener() {
>             public void actionPerformed(ActionEvent e) {
>                r.run();
>             }
>         });
>         t.setRepeats(false);
>         t.start();
>     }
>
> But then for the second method one would need to
> track the created timers, so as to be able to
> selectively stop them.

A first stab:

Keep a WeakHashMap<Runnable,Collection<Reference<Timer>>>, making all 
changes on the EDT.  Store weak references to each created Timer, in a 
HashSet per Runnable.

When asked to remove all callbacks, remove the Runnable from the map, 
get its Collection of Timers, and stop them.  If the references have 
already expired, you don't care.  When all the Timers using the same 
Runnable have expired, assuming that they naturally decay, the map entry 
will be removed anyway.

   // uncompiled
   void removeCallbacks(final Runnable r) {
     invokeAndWait(new Runnable() {
       public void run() {
         Collection<Reference<Timer>>  timers = map.remove(r);
         if (timers == null) return;
         for (Reference<Timer>  rt : timers) {
           Timer t = rt.get();
           if (t != null) t.stop();
         }
       }
     });
   }

   void postDelayed(final Runnable r, int d) {
     final Timer t=new Timer(d,new ActionListener() {
       public void actionPerformed(ActionEvent e) {
         r.run();
       }
     });
     invokeAndWait(new Runnable() {
       public void run() {
         Collection<Reference<Timer>>  coll = map.get(r);
         if (coll == null) {
           coll = new HashSet<Reference<Timer>>();
           map.put(r, coll);
         }
         coll.add(new WeakReference<Timer>(t));
       }
     });
     // should use d too!
     t.setRepeats(false);
     t.start();
   }




-- 
ss at comp dot lancs dot ac dot uk