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• Application.Current.Shutdown() vs. Application.Current.Dispatcher.BeginInvokeShutdown()

  - by Daniel Rose

  First a bit of background: I have a WPF application, which is a GUI-front-end to a legacy Win32-application. The legacy app runs as DLL in a separate thread. The commands the user chooses in the UI are invoked on that "legacy thread". If the "legacy thread" finishes, the GUI-front-end cannot do anything useful anymore, so I need to shutdown the WPF-application. Therefore, at the end of the thread's method, I call Application.Current.Shutdown(). Since I am not on the main thread, I need to invoke this command. However, then I noticed that the Dispatcher also has BeginInvokeShutdown() to shutdown the dispatcher. So my question is: What is the difference between invoking Application.Current.Shutdown(); and calling Application.Current.Dispatcher.BeginInvokeShutdown();

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• Gracefully exiting from thread in Ruby

  - by jasonbogd

  Hi, I am trying out Mongrel and using the following code: require 'rubygems' require 'mongrel' class SimpleHandler < Mongrel::HttpHandler def process(request, response) response.start(200) do |head, out| head["Content-Type"] = "text/plain" out.write("Hello World!\n") end end end h = Mongrel::HttpServer.new("0.0.0.0", "3000") h.register("/test", SimpleHandler.new) puts "Press Control-C to exit" h.run.join trap("INT") do puts "Exiting..." end Basically, this just prints out "Hello World!" when I go to localhost:3000/test. It works fine, and I can close the program with Control-C. But when I press Control-C, this gets outputted: my_web_server.rb:17:in `join': Interrupt from my_web_server.rb:17 So I tried putting that trap("INT") statement at the end, but it isn't getting called. Solution? Thanks.

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• Is RegSetValueEx thread safe?

  - by Brent Newbury

  I suspect that RegSetValueEx is thread safe, but would like some confirmation from the community. If called from multiple threads, will there be any side effects? The RegSetValueEx MSDN documentation doesn't mention thread safety at all.

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• Deadlock in Java

  - by israkir

  Long time ago, I saved a sentence from a Java reference book: "Java has no mechanism to handle deadlock. it won't even know deadlock occurred." (Head First Java 2nd Edition, p.516) So, what is about it? Is there a way to catch deadlock case in Java? I mean, is there a way that our code understands a deadlock case occurred?

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• Is this (Lock-Free) Queue Implementation Thread-Safe?

  - by Hosam Aly

  I am trying to create a lock-free queue implementation in Java, mainly for personal learning. The queue should be a general one, allowing any number of readers and/or writers concurrently. Would you please review it, and suggest any improvements/issues you find? Thank you. import java.util.concurrent.atomic.AtomicReference; public class LockFreeQueue<T> { private static class Node<E> { E value; volatile Node<E> next; Node(E value) { this.value = value; } } private AtomicReference<Node<T>> head, tail; public LockFreeQueue() { // have both head and tail point to a dummy node Node<T> dummyNode = new Node<T>(null); head = new AtomicReference<Node<T>>(dummyNode); tail = new AtomicReference<Node<T>>(dummyNode); } /** * Puts an object at the end of the queue. */ public void putObject(T value) { Node<T> newNode = new Node<T>(value); Node<T> prevTailNode = tail.getAndSet(newNode); prevTailNode.next = newNode; } /** * Gets an object from the beginning of the queue. The object is removed * from the queue. If there are no objects in the queue, returns null. */ public T getObject() { Node<T> headNode, valueNode; // move head node to the next node using atomic semantics // as long as next node is not null do { headNode = head.get(); valueNode = headNode.next; // try until the whole loop executes pseudo-atomically // (i.e. unaffected by modifications done by other threads) } while (valueNode != null && !head.compareAndSet(headNode, valueNode)); T value = (valueNode != null ? valueNode.value : null); // release the value pointed to by head, keeping the head node dummy if (valueNode != null) valueNode.value = null; return value; }

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• Writing to a log4net FileAppender with multiple threads performance problems

  - by Wayne

  TickZoom is a very high performance app which uses it's own parallelization library and multiple O/S threads for smooth utilization of multi-core computers. The app hits a bottleneck where users need to write information to a LogAppender from separate O/S threads. The FileAppender uses the MinimalLock feature so that each thread can lock and write to the file and then release it for the next thread to write. If MinimalLock gets disabled, log4net reports errors about the file being already locked by another process (thread). A better way for log4net to do this would be to have a single thread that takes care of writing to the FileAppender and any other threads simply add their messages to a queue. In that way, MinimalLock could be disabled to greatly improve performance of logging. Additionally, the application does a lot of CPU intensive work so it will also improve performance to use a separate thread for writing to the file so the CPU never waits on the I/O to complete. So the question is, does log4net already offer this feature? If so, how do you do enable threaded writing to a file? Is there another, more advanced appender, perhaps? If not, then since log4net is already wrapped in the platform, that makes it possible to implement a separate thread and queue for this purpose in the TickZoom code. Sincerely, Wayne

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• Matplotlib and WSGI/mod_python not working on Apache.

  - by Luiz C.

  Everything works as supposed to on the Django development server. In Apache, the django app also works except when matplotlib is used. Here's the error I get: No module named multiarray. Exception Type: ImportError Exception Value: No module named multiarray Exception Location: /usr/share/pyshared/numpy/core/numerictypes.py in <module>, line 81 Python Executable: /usr/bin/python Python Version: 2.6.4 From the python shell, both statements work: import numpy.core.multiarray and import multiarray. Any ideas? Thanks As I'm looking over the numpy files, I found the multiarray module, which has an extension of 'so'. My guess, is that mod_python is not reading these files.

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• How upload files to azure in background with Delphi and OmniThread?

  - by mamcx

  I have tried to upload +100 files to azure with Delphi. However, the calls block the main thread, so I want to do this with a async call or with a background thread. This is what I do now (like explained here): procedure TCloudManager.UploadTask(const input: TOmniValue; var output: TOmniValue); var FileTask:TFileTask; begin FileTask := input.AsRecord<TFileTask>; Upload(FileTask.BaseFolder, FileTask.LocalFile, FileTask.CloudFile); end; function TCloudManager.MassiveUpload(const BaseFolder: String; Files: TDictionary<String, String>): TStringList; var pipeline: IOmniPipeline; FileInfo : TPair<String,String>; FileTask:TFileTask; begin // set up pipeline pipeline := Parallel.Pipeline .Stage(UploadTask) .NumTasks(Environment.Process.Affinity.Count * 2) .Run; // insert URLs to be retrieved for FileInfo in Files do begin FileTask.LocalFile := FileInfo.Key; FileTask.CloudFile := FileInfo.Value; FileTask.BaseFolder := BaseFolder; pipeline.Input.Add(TOmniValue.FromRecord(FileTask)); end;//for pipeline.Input.CompleteAdding; // wait for pipeline to complete pipeline.WaitFor(INFINITE); end; However this block too (why? I don't understand).

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• Do Scala and Erlang use green threads?

  - by CHAPa

  I've been reading a lot about how Scala and Erlang does lightweight threads and their concurrency model (actors). However, I have my doubts. Do Scala and Erlang use an approach similar to the old thread model used by Java (green threads) ? For example, suppose that there is a machine with 2 cores, so the Scala/Erlang environment will fork one thread per processor? The other threads will be scheduled by user-space (Scala VM / Erlang VM ) environment. Is this correct? Under the hood, how does this really work?

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• Winforms application hangs when switching to another app

  - by joseluisrod

  Hi, I believe I have a potential threading issue. I have a user control that contains the following code: private void btnVerify_Click(object sender, EventArgs e) { if (!backgroundWorkerVerify.IsBusy) { backgroundWorkerVerify.RunWorkerAsync(); } } private void backgroundWorkerVerify_DoWork(object sender, System.ComponentModel.DoWorkEventArgs e) { VerifyAppointments(); } private void backgroundWorkerVerify_RunWorkerCompleted(object sender, System.ComponentModel.RunWorkerCompletedEventArgs e) { MessageBox.Show("Information was Verified.", "Verify", MessageBoxButtons.OK, MessageBoxIcon.Information); CloseEvent(); } vanilla code. but the issue I have is that when the application is running and the users tabs to another application when they return to mine the application is hung, they get a blank screen and they have to kill it. This started when I put the threading code. Could I have some rogue threads out there? what is the best way to zero in a threading problem? The issue can't be recreated on my machine...I know I must be missing something on how to dispose of a backgroundworker properly. Any thoughts are appreciated, Thanks, Jose

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• Hooking thread exit

  - by mackenir

  Is there a way for me to hook the exit of managed threads (i.e. run some code on a thread, just before it exits?) I've developed a mechanism for hooking thread exit that works for some threads. Step 1: develop a 'hook' STA COM class that takes a callback function and calls it in its destructor. Step 2: create a ThreadStatic instance of this object on the thread I want to hook, and pass the object a managed delegate converted to an unmanaged function pointer. The delegate then gets called on thread exit (since the CLR calls IUnknown::Release on all STA COM RCWs as part of thread exit). This mechanism works on, for example, worker threads that I create in code using the Thread class. However, it doesn't seem to work for the application's main thread (be it a console or windows app). The 'hook' COM object seems to be deleted too late in the shutdown process and the attempt to call the delegate fails. (The reason I want to implement this facility is so I can run some native COM code on the exiting thread that works with STA COM objects that were created on the thread, before it's 'too late' (i.e. before the thread has exited, and it's no longer possible to work with STA COM objects on that thread.))

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• Please help. Creating threads and wait till finsh

  - by Raj Aththanayake

  Hi I have two method calls that I want to call using two threads. Then I want them to wait till method executions get completed before continuing. My sample solution is something like below. public static void Main() { Console.WriteLine("Main thread starting."); String[] strThreads = new String[] { "one", "two" }; String ctemp = string.Empty; foreach (String c in strThreads) { ctemp = c; Thread thread = new Thread(delegate() { MethodCall(ctemp); }); thread.Start(); thread.Join(); } Console.WriteLine("Main thread ending."); Console.Read(); } public static void MethodCalls(string number) { Console.WriteLine("Method call " + number); } Is this will do the job? Or is there another better way to do the same thing?

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• libclntsh.so.11.1: cannot open shared object file.

  - by zhangzhong

  I want to schedule a task on linux by icrontab, and the task is written in python and have to import cx_Oracle module, so I export ORACLE_HOME and LD_LIBRARY_PATH in .bash_profile, but it raise the error: libclntsh.so.11.1: cannot open shared object file. Since it is ok to run the task by issue the command in shell like python a.py # ok I change the task in icrontab into a shell script which invoke my python script, but the exception recurred? # the shell script scheduled in icrontab #! bash python a.py Could you help how to do with it?

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• JScrollPane Scrolls Down with Long Text in JEditorPane

  - by Jim

  Hello, I want to have a JEditorPane inside a JScrollPane. When the user clicks a button, the click listener will create a textEditor, call jscrollpane.setViewPort(textEditor), call textEditor.setText(String) to fill it with editable text, and call jscrollpane.getVerticalScrollBar().setValue(0). In case you're wondering, yes, the setText() must come after the setViewPort() for reasons that aren't on topic. Here is the problem: After the user clicks the button, the JScrollPane's view scrolls all the way to the bottom. I want the scrollbar to be at the top, as per the last line in my click listener. I popped open a debugger, and to my horror, discovered that the jscrollpane's viewport is being forced down to the bottom after the conclusion of the click listener (when pumping filters). It appears that Swing is delaying the population of the editor/jscrollpane until after the conclusion of the clicklistener, but is calling the scrollbar command first. Thus, the undesired behavior. Anyway, I'm wondering if there is a clean solution. It seems that wanting a scrollpane to be scrolled to the top after modification would be a reasonably common requirement, so I'm assuming this is a well-solved problem. Thanks!

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• Cross Thread Exception in PropertyChangedEvent in WPF

  - by Ashish Ashu

  I have a ListView that is binded to my custom collection. At run time , I am updating the certain properties of my entity in my custom collection in my ViewModel. At the same time , I am also doing the custom sorting in the listview. The custom sorting is applicable when I click on the any column header of the listview. For example, I am updating the current datetime on my entity on every 5 seconds and simulaneously , I am applying custom sorting based on DateTime. (The Listview is third party control). Hence I am doing two operations on my custom collection at the same time. Should I pass the dispatcher of my control in the view model and call any methods ( which updates any entity in my custom collection ) through UI dispatcher ?

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• How to mmap the stack for the clone() system call on linux?

  - by Joseph Garvin

  The clone() system call on Linux takes a parameter pointing to the stack for the new created thread to use. The obvious way to do this is to simply malloc some space and pass that, but then you have to be sure you've malloc'd as much stack space as that thread will ever use (hard to predict). I remembered that when using pthreads I didn't have to do this, so I was curious what it did instead. I came across this site which explains, "The best solution, used by the Linux pthreads implementation, is to use mmap to allocate memory, with flags specifying a region of memory which is allocated as it is used. This way, memory is allocated for the stack as it is needed, and a segmentation violation will occur if the system is unable to allocate additional memory." The only context I've ever heard mmap used in is for mapping files into memory, and indeed reading the mmap man page it takes a file descriptor. How can this be used for allocating a stack of dynamic length to give to clone()? Is that site just crazy? ;) In either case, doesn't the kernel need to know how to find a free bunch of memory for a new stack anyway, since that's something it has to do all the time as the user launches new processes? Why does a stack pointer even need to be specified in the first place if the kernel can already figure this out?

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• ThreadPooler in Spring 2.5.6

  - by MiKu

  My application uses Spring 2.5.6. I have a service that creates explicit threads for some specific task. Triggering of this service call happens through quartz time scheduler. Question : While executing service calls, i want to use some sort of thread pooler that can return me thread instances. Is there any implementations that i can use in Spring?

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• Non-reentrant C# timer

  - by Oak

  I'm trying to invoke a method f() every t time, but if the previous invocation of f() has not finished yet, wait until it's finished. I've read a bit about the available timers (this is a useful link) but couldn't find any good way of doing what I want, save for manually writing it all. Any help about how to achieve this will be appreciated, though I fear I might not be able to find a simple solution using timers. To clarify, if x is one second, and f() runs the arbitrary durations I've written below, then: Step Operation Time taken 1 wait 1s 2 f() 0.6s 3 wait 0.4s (because f already took 0.6 seconds) 4 f() 10s 5 wait 0s (we're late) 6 f() 0.3s 7 wait 0.7s (we can disregard the debt from step 4) Notice that the nature of this timer is that f() will not need to be safe regarding re-entrance, and a thread pool of size 1 is enough here.

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• Threading is slow and unpredictable?

  - by Jake

  I've created the basis of a ray tracer, here's my testing function for drawing the scene: public void Trace(int start, int jump, Sphere testSphere) { for (int x = start; x < scene.SceneWidth; x += jump) { for (int y = 0; y < scene.SceneHeight; y++) { Ray fired = Ray.FireThroughPixel(scene, x, y); if (testSphere.Intersects(fired)) sceneRenderer.SetPixel(x, y, Color.Red); else sceneRenderer.SetPixel(x, y, Color.Black); } } } SetPixel simply sets a value in a single dimensional array of colours. If I call the function normally by just directly calling it it runs at a constant 55fps. If I do: Thread t1 = new Thread(() => Trace(0, 1, testSphere)); t1.Start(); t1.Join(); It runs at a constant 50fps which is fine and understandable, but when I do: Thread t1 = new Thread(() => Trace(0, 2, testSphere)); Thread t2 = new Thread(() => Trace(1, 2, testSphere)); t1.Start(); t2.Start(); t1.Join(); t2.Join(); It runs all over the place, rapidly moving between 30-40 fps and sometimes going out of that range up to 50 or down to 20, it's not constant at all. Why is it running slower than it would if I ran the whole thing on a single thread? I'm running on a quad core i5 2500k.

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• How do you implement Software Transactional Memory?

  - by Joseph Garvin

  In terms of actual low level atomic instructions and memory fences (I assume they're used), how do you implement STM? The part that's mysterious to me is that given some arbitrary chunk of code, you need a way to go back afterward and determine if the values used in each step were valid. How do you do that, and how do you do it efficiently? This would also seem to suggest that just like any other 'locking' solution you want to keep your critical sections as small as possible (to decrease the probability of a conflict), am I right? Also, can STM simply detect "another thread entered this area while the computation was executing, therefore the computation is invalid" or can it actually detect whether clobbered values were used (and thus by luck sometimes two threads may execute the same critical section simultaneously without need for rollback)?

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• What does binding mean exactly?

  - by Lily

  I always see people mention that "Python binding" and "C Sharp binding" etc. when I am actually using their C++ libraries. What does binding mean? If the library is written in C, and does Python binding means that they use SWIG kind of tool to mock a Python interface? Newbie in this field, and any suggestion will be welcomed.

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• Assigning a property across threads

  - by Mike

  I have set a property across threads before and I found this post http://stackoverflow.com/questions/142003/cross-thread-operation-not-valid-control-accessed-from-a-thread-other-than-the-t about getting a property. I think my issue with the code below is setting the variable to the collection is an object therefore on the heap and therefore is just creating a pointer to the same object So my question is besides creating a deep copy, or copying the collection into a different List object is there a better way to do the following to aviod the error during the for loop. Cross-thread operation not valid: Control 'lstProcessFiles' accessed from a thread other than the thread it was created on. Code: private void btnRunProcess_Click(object sender, EventArgs e) { richTextBox1.Clear(); BackgroundWorker bg = new BackgroundWorker(); bg.DoWork += new DoWorkEventHandler(bg_DoWork); bg.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bg_RunWorkerCompleted); bg.RunWorkerAsync(lstProcessFiles.SelectedItems); } void bg_DoWork(object sender, DoWorkEventArgs e) { WorkflowEngine engine = new WorkflowEngine(); ListBox.SelectedObjectCollection selectedCollection=null; if (lstProcessFiles.InvokeRequired) { // Try #1 selectedCollection = (ListBox.SelectedObjectCollection) this.Invoke(new GetSelectedItemsDelegate(GetSelectedItems), new object[] { lstProcessFiles }); // Try #2 //lstProcessFiles.Invoke( // new MethodInvoker(delegate { // selectedCollection = lstProcessFiles.SelectedItems; })); } else { selectedCollection = lstProcessFiles.SelectedItems; } // *********Same Error on this line******************** // Cross-thread operation not valid: Control 'lstProcessFiles' accessed // from a thread other than the thread it was created on. foreach (string l in selectedCollection) { if (engine.LoadProcessDocument(String.Format(@"C:\TestDirectory\{0}", l))) { try { engine.Run(); WriteStep(String.Format("Ran {0} Succussfully", l)); } catch { WriteStep(String.Format("{0} Failed", l)); } engine.PrintProcess(); WriteStep(String.Format("Rrinted {0} to debug", l)); } } } private delegate void WriteDelegate(string p); private delegate ListBox.SelectedObjectCollection GetSelectedItemsDelegate(ListBox list); private ListBox.SelectedObjectCollection GetSelectedItems(ListBox list) { return list.SelectedItems; }

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• QProcess, QEventLoop - of any use for parallel-processing

  - by dlib

  I wonder whether I could use QEventLoop (QProcess?) to parallelize multiple calls to same function with Qt. What is precisely the difference with QtConcurrent or QThread? What is a process and an event loop more precisely? I read that QCoreApplication must exec() as early as possible in main() method, so that I wonder why it is different from main Thread. could you point as some efficient reference to processes and thread with Qt? I came through the official doc and those things remain unclear. Thanks and regards.

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• Socket server with multiple clients, sending messages to many clients without hurting liveliness

  - by Karl Johanson

  I have a small socket server, and I need to distribute various messages from client-to-client depending on different conditionals. However I think I have a small problem with livelyness in my current code, and is there anything wrong in my approach: public class CuClient extends Thread { Socket socket = null; ObjectOutputStream out; ObjectInputStream in; CuGroup group; public CuClient(Socket s, CuGroup g) { this.socket = s; this.group = g; out = new ObjectOutputStream(this.socket.getOutputStream()); out.flush(); in = new ObjectInputStream(this.socket.getInputStream()); } @Override public void run() { String cmd = ""; try { while (!cmd.equals("client shutdown")) { cmd = (String) in.readObject(); this.group.broadcastToGroup(this, cmd); } out.close(); in.close(); socket.close(); } catch (Exception e) { System.out.println(this.getName()); e.printStackTrace(); } } public void sendToClient(String msg) { try { this.out.writeObject(msg); this.out.flush(); } catch (IOException ex) { } } And my CuGroup: public class CuGroup { private Vector<CuClient> clients = new Vector<CuClient>(); public void addClient(CuClient c) { this.clients.add(c); } void broadcastToGroup(CuClient clientName, String cmd) { Iterator it = this.clients.iterator(); while (it.hasNext()) { CuClient cu = (CuClient)it.next(); cu.sendToClient(cmd); } } } And my main-class: public class SmallServer { public static final Vector<CuClient> clients = new Vector<CuClient>(10); public static boolean serverRunning = true; private ServerSocket serverSocket; private CuGroup group = new CuGroup(); public void body() { try { this.serverSocket = new ServerSocket(1337, 20); System.out.println("Waiting for clients\n"); do { Socket s = this.serverSocket.accept(); CuClient t = new CuClient(s,group); System.out.println("SERVER: " + s.getInetAddress() + " is connected!\n"); t.start(); } while (this.serverRunning); } catch (IOException ex) { ex.printStackTrace(); } } public static void main(String[] args) { System.out.println("Server"); SmallServer server = new SmallServer(); server.body(); } } Consider the example with many more groups, maybe a Collection of groups. If they all synchronize on a single Object, I don't think my server will be very fast. I there a pattern or something that can help my liveliness?

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• I/O between AIR client using Native process and executable java .jar

  - by aseem behl

  I am using Adobe AIR 2.0 native process API to launch a java executable jar. I/O is handled by writing to the input stream of the java process and reading from the output stream. The application is event based where several events are fired from the server. We catch these events in java code, handle them and write the output to the outputstream using the synchronized static method below. public class ReaderWriter { static Logger logger = Logger.getLogger(ReaderWriter.class); public synchronized static void writeToAir(String output){ try{ byte[] byteArray = output.getBytes(); DataOutputStream dataOutputStream = new DataOutputStream(System.out); dataOutputStream.write(byteArray); dataOutputStream.flush(); } catch (IOException e) { logger.info("Exception while writing the output. " + e); } } } The issue is that some messages are lost between the transfer and not all messages reach the AIR client. If I run the java application from the console I am receiving all the messages. It would be great if somebody could point out what I am missing. Following are some of the listeners used to send the event data to the AIR client. // class used to process Shutdown events from the Session private class SessionShutdownListener implements SessionListener{ public void onEvent(Event e) { Session.Shutdown sd = (Session.Shutdown) e; Session.ShutdownReason sr = sd.getReason(); String eventOutput = "eo;" + "Session Shutdown event ocurred reason=" + sr.strValue() + "\n"; ReaderWriter.writeToAir(eventOutput); } } // class used to process OperationSucceeded events from the Session private class SessionOperationSucceededListener implements SessionListener{ public void onEvent(Event e) { Session.OperationSucceeded os = (Session.OperationSucceeded) e; String eventOutput = "eo;" + "Session OperationSucceeded event ocurred" + "\n"; ReaderWriter.writeToAir(eventOutput); } }

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