StackOverflow2013

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POClever asynchronous repaint in Java
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copied!<p>I have a use-case coming from a GUI problem I would like to submit to your sagacity. </p> <p><strong>Use case</strong></p> <p>I have a GUI that displays a computation result depending on some parameters the user set in a GUI. For instance, when the user moves a slider, several events are fired, that all trigger a new computation. When the user adjust the slider value from A to B, a dozens of events are fired.</p> <p>But the computation can take up to several seconds, whereas the slider adjustment can fire an event every few 100 ms.</p> <p>How to write a proper Thread that would listen to these events, and kind of filter them so that the repaint of the results is lively? Ideally you would like something like</p> <ul> <li>start a new computation as soon as first change event is received;</li> <li>cancel the first computation if a new event is received, and start a new one with the new parameters;</li> <li>but ensure that the last event will not be lost, because the last completed computation needs to be the one with last updated parameters. </li> </ul> <p><strong>What I have tried</strong></p> <p>A friend of mine (A. Cardona) proposed this low level approach of an Updater thread that prevents too many events to trigger a computation. I copy-paste it here (GPL):</p> <p>He puts this in a class that extends Thread:</p> <pre class="lang-java prettyprint-override"><code>public void doUpdate() { if (isInterrupted()) return; synchronized (this) { request++; notify(); } } public void quit() { interrupt(); synchronized (this) { notify(); } } public void run() { while (!isInterrupted()) { try { final long r; synchronized (this) { r = request; } // Call refreshable update from this thread if (r > 0) refresh(); // Will trigger re-computation synchronized (this) { if (r == request) { request = 0; // reset wait(); } // else loop through to update again } } catch (Exception e) { e.printStackTrace(); } } } public void refresh() { // Execute computation and paint it ... } </code></pre> <p>Every-time an event is sent by the GUI stating that parameters have been changed, we call <code>updater.doUpdate()</code>. This causes the method <code>refresh()</code> to be called much less. But I have no control on this.</p> <p><strong>Another way?</strong></p> <p>I was wondering if there is another way to do that, that would use the jaca.concurrent classes. But I could not sort in the Executors framework what would be the one I should start with.</p> <p>Does any of you have some experience with a similar use case? </p> <p>Thanks</p>

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