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POCalling Looper more than once causes "sending message to a Handler on a dead thread"
 

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  1. POCalling Looper more than once causes "sending message to a Handler on a dead thread"
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    <p>I am using an Executor [fixed thread pool] with my own ThreadFactory that adds a Looper:</p> <pre><code>Handler HANDLER = new Handler(); Executor THREADS = Executors.newFixedThreadPool(THREAD_POOL_SIZE, new ThreadFactory() { @Override public Thread newThread(Runnable runnable) { return new MyThread(new Runnable() { @Override public void run() { Looper.prepare(); runnable.run(); } }); } }); private static class MyHandler extends Handler { public boolean fail; public void handleMessage(Message msg) { switch(msg.what) { case 1: this.fail = msg.arg1 == 1; Looper.myLooper().quit(); break; } } } } </code></pre> <p>I am running a thread that makes network requests but if the network fails I would like a dialog message to be displayed to the user. This process is rather involving since it requires making AND displaying the request in the UI thread. I can wait for the user's response to the dialog by simply adding a Loop to the network thread and wait for a message to be send from the UI thread. This allows me to encapsulate the network requests in a while(tryAgain) thread. All works well except when the Looper.loop() method is called the second time (after a second network error dialog is displayed) and a message is sent by the dialog (in the UI thread) to the network thread's handler:</p> <pre><code>THREADS.execute(new Runnable() { private MyHandler myHandler = new MyHandler(); @Override public void run() { boolean tryAgain = true; while(tryAgain) { try { switch(request) { [Handle network requests] } tryAgain = false; } catch(IOException e) { // The network is unavailable. Ask the user if we should try again. e.printStackTrace(); } finally { if(tryAgain) { HANDLER.post(new Runnable() { // The UI thread @Override public void run() { theAlertDialog.show(); } }); // Wait for the results from the dialog which lives in the UI thread. Looper.loop(); // At this point the dialog has informed us of our answer. tryAgain = !myHandler.fail; } } } } }); </code></pre> <p>In the AlertDialog instance is an OnClickListener:</p> <pre><code>DialogInterface.OnClickListener myOnclickListener = new DialogInterface.OnClickListener() { public void onClick(DialogInterface dialog, int id) { Message msg = myHandler.obtainMessage(1); msg.setTarget(this.handler); msg.sendToTarget(); } } </code></pre> <p>I've checked that the thread is still active with <code>handler.getLooper().getThread().isAlive()</code> which always returns true but it still gives me "sending message to a Handler on a dead thread". How is it that the Message/Handler has decided that the thread is dead? Shouldn't it rely on the .isAlive() method? In the end I am trying to avoid replicating the thread management build into the Android OS :-)</p>
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