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From: Jan Burse <janburse@fastmail.fm>
Newsgroups: comp.lang.java.programmer
Subject: Re: Lightweight postDelayed / removeCallbacks
Date: Mon, 06 Feb 2012 01:15:14 +0100
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Steven Simpson schrieb:
 > A first stab:

Thank you very much for your solution. Since I
was in need of a solution I implemented already
something yesterday.

Difference to your stab: postDelayed() and
removeCallbacks() do not wait for mouse /
keyevents / etc.. to flush. The problem
is that invokeAndWait() calls postEvent(),
which calls flushPendingEvents() in turn.

The Android removeCallbacks() and postDelayed()
are also immediate. They call in turn
removeMessages() respectively enqueueMessage()
which are immediate.

I didn't use javax.swing.Timer since I still
think they are not leightweight enough. So
my waiting is done via Object.wait(), whereas
the Swing timer uses Condition.awaitNanos().
Not sure what is more reliable.

I also use System.currentTimeMillis() whereas
the Swing timer uses System.nanoTime(). nanoTime()
is more stable, it does not change when the
wall clock is changed on the computer.

But current solution is then to use tail
recursion for a looping animation. Which
can get jerky, since the rate will be not
fixed. The delivery of the event might still
take some time before a next postDelayed()
happens, since it is delivered via postEvent()
which uses flushPendingEvents(). But this is
tollerated in the current application.

Could use a post with runnable = null to stop
the thread, something similar is done in the
Android looper. But currently the thread has to
be started via start(), and can then be easily
terminated via interrupt().

---------------- Begin Code ------------------

public class ThreadTimer extends Thread {
     private final ArrayList<TimerEntry> entrylist =
        new ArrayList<TimerEntry>();
     private final Object entrylock = new Object();

     public void postDelayed(Runnable r, int d) {
         TimerEntry entry = new TimerEntry(r,
             System.currentTimeMillis() + d);
         synchronized (entrylock) {
             for (int i = 0; i < entrylist.size(); i++) {
                 TimerEntry entry2 = entrylist.get(i);
                 if (entry.getWhen() < entry2.getWhen()) {
                     entrylist.add(i, entry);
                     entrylock.notifyAll();
                     return;
                 }
             }
             entrylist.add(entry);
             entrylock.notifyAll();
         }
     }

     public void removeCallbacks(Runnable r) {
         synchronized (entrylock) {
             int backsize = entrylist.size();
             for (int i = entrylist.size() - 1; i >= 0; i--) {
                 TimerEntry entry = entrylist.get(i);
                 if (entry.getRunnable() == r)
                     entrylist.remove(i);
             }
             if (backsize != entrylist.size())
                 entrylock.notifyAll();
         }
     }

     private TimerEntry take() throws InterruptedException {
         for (; ; ) {
             synchronized (entrylock) {
                 if (entrylist.size() == 0) {
                     entrylock.wait();
                 } else {
                     TimerEntry entry = entrylist.get(0);
                     long now = System.currentTimeMillis();
                     if (entry.getWhen() <= now) {
                         entrylist.remove(0);
                         return entry;
                     } else {
                         entrylock.wait(entry.getWhen() - now);
                     }
                 }
             }
         }
     }

     public void run() {
         try {
             for (; ; ) {
                 TimerEntry entry = take();
                 SwingUtilities.invokeLater(entry.getRunnable());
             }
         } catch (InterruptedException x) {
             /* */
         }
     }

}

class TimerEntry {
     private final Runnable runnable;
     private final long when;

     TimerEntry(Runnable r, long w) {
         runnable = r;
         when = w;
     }

     Runnable getRunnable() {
         return runnable;
     }

     long getWhen() {
         return when;
     }

}

---------------- End Code --------------------