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POUsing ExecutorService and ProgressMonitor in a Thread Safe Manner
 

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  1. POUsing ExecutorService and ProgressMonitor in a Thread Safe Manner
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    <p>I first define the ProgressMonitor:</p> <pre><code>progressMonitor = new ProgressMonitor(parent, "Starting processing ...", "", 0, maxNumberProcesses+1); progressMonitor.setProgress(0); </code></pre> <p>and on the same thread use an ExecutorService and invokeAll() to process a list of Callables:</p> <pre><code>ExecutorService execService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors()); // use all available processors at startup execService.invokeAll(callables); // wait for all tasks to complete execService.shutdownNow(); // free thread pool resources </code></pre> <p>Each Callable is of the form:</p> <pre><code>class Callable implements Callable&lt;List&lt;String&gt;&gt; { public List&lt;String&gt; call() { List&lt;String&gt; files = doSomeStuff(); progressBarUpdate(); return files; } } </code></pre> <p>ie; each Callable calls progressBarUpdate():</p> <pre><code>private void progressBarUpdate() { if (progressMonitor != null) { Lock lock = new ReentrantLock(); lock.lock(); try { progressMonitor.increment(); } finally { lock.unlock(); // release lock } } } </code></pre> <p>Each doSomeStuff() has its own exception handling and if an error occurs or an exception is thrown then a null value is returned. This is why the return type is a List, and returns null in such cases. There is no crossover between the Callables and the List of files they return, they all maintain there own list of files.</p> <p>I find that it works fine but occasionally it throws an InterruptedException of the form:</p> <pre><code>Disposal was interrupted: java.lang.InterruptedException at java.lang.Object.wait(Native Method) at java.lang.Object.wait(Object.java:503) at java.awt.EventQueue.invokeAndWait(EventQueue.java:1263) at java.awt.Window.doDispose(Window.java:1209) at java.awt.Dialog.doDispose(Dialog.java:1196) at java.awt.Window.dispose(Window.java:1147) at javax.swing.ProgressMonitor.close(ProgressMonitor.java:311) at javax.swing.ProgressMonitor.setProgress(ProgressMonitor.java:264) </code></pre> <p>showing that setProgress() calls close() when the monitor max is reached:</p> <pre><code>public void setProgress(int nv) { if (nv &gt;= max) { close(); } ... </code></pre> <p>and close() contains numerous other non-thread safe calls.</p> <p>I've modified my code so that the condition nv>=max is not satisfied and I explicitly call ProgressMonitor.close() after invokeAll(), but I'm still not convinced that such an approach is completely thread safe.</p> <p>Has anyone else encountered this situation and found a rock-solid solution?</p> <p>Thanks</p> <p>Graham</p> <p>PS. Note that ProgressMonitor is not a swing widget but does encapsulate Swing components. As a result I ensure that ProgressMonitor does not run on the EDT.</p>
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    1. USGraham Seed
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    1. COWhich class is progressBarUpdate() part of? And, how does it receive progressMonitor?
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      1. USSlava Imeshev
    2. COIt's a member of the same class with the ExecutorService and Callables list. The ProgressMonitor is a field since it is called by all Callables.
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