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• Threading Problems in ActionScript 2.0?

  - by yar

  Is it possible to have concurrency problems (thread competition) in an onEnterFrame method in ActionScript 2.0? I have written this cheesy code as a guard: if (!busy) { // I suspect some threading problems: is that even possible in flash busy = true; movePanels(); busy = false; } but this is no assurance against thread competition. If so, how can I do a basic semaphore/lock? Note: I suspect threading problems in my app, but if they're impossible, I'll check my code differently.

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• Looking for suggestions about an architecture of a MultiThreaded app.

  - by Dimitri

  Hello everyone. I am looking to develop a multithreaded application that will be running in unconditional loop and processing high volume of data. High volume is 2000+ records per minute. Processing will involve data retrieval, calculations and data updates. I need the application to perform so that there is virtually no back log, meaning i need to be able to finish up all of the 2000 points in one minute or even faster. Our current implementation features a multithreaded application that is spawn multiple times (from 10 to 20) and we are noticing that it's not handling data as expected and i even feel that instances of the application compete with each other for processor time and eventually if not slowing, not benefiting each other for sure. I would like to know what would be the best approach: have a single instance running but maximize threads that can run simultaneously? or is there other ways i don't know? I'm open to suggestions. Thank you in advance

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• Java Thread - Synchronization issue

  - by Yatendra Goel

  From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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• A generic C++ library that provides QtConcurrent functionality?

  - by Lucas

  QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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• Repeated host lookups failing in urllib2

  - by reve_etrange

  I have code which issues many HTTP GET requests using Python's urllib2, in several threads, writing the responses into files (one per thread). During execution, it looks like many of the host lookups fail (causing a name or service unknown error, see appended error log for an example). Is this due to a flaky DNS service? Is it bad practice to rely on DNS caching, if the host name isn't changing? I.e. should a single lookup's result be passed into the urlopen? Exception in thread Thread-16: Traceback (most recent call last): File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner self.run() File "/home/da/local/bin/ThreadedDownloader.py", line 61, in run page = urllib2.urlopen(url) # get the page File "/usr/lib/python2.6/urllib2.py", line 126, in urlopen return _opener.open(url, data, timeout) File "/usr/lib/python2.6/urllib2.py", line 391, in open response = self._open(req, data) File "/usr/lib/python2.6/urllib2.py", line 409, in _open '_open', req) File "/usr/lib/python2.6/urllib2.py", line 369, in _call_chain result = func(*args) File "/usr/lib/python2.6/urllib2.py", line 1170, in http_open return self.do_open(httplib.HTTPConnection, req) File "/usr/lib/python2.6/urllib2.py", line 1145, in do_open raise URLError(err) URLError: <urlopen error [Errno -2] Name or service not known>

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• boost thread pool

  - by Dtag

  I need a threadpool for my application, and I'd like to rely on standard (C++11 or boost) stuff as much as possible. I realize there is an unofficial(!) boost thread pool class, which basically solves what I need, however I'd rather avoid it because it is not in the boost library itself -- why is it still not in the core library after so many years? In some posts on this page and elsewhere, people suggested using boost::asio to achieve a threadpool like behavior. At first sight, that looked like what I wanted to do, however I found out that all implementations I have seen have no means to join on the currently active tasks, which makes it useless for my application. To perform a join, they send stop signal to all the threads and subsequently join them. However, that completely nullifies the advantage of threadpools in my use case, because that makes new tasks require the creation of a new thread. What I want to do is: ThreadPool pool(4); for (...) { for (int i=0;i<something;i++) pool.pushTask(...); pool.join(); // do something with the results } Can anyone suggest a solution (except for using the existing unofficial thread pool on sourceforge)? Is there anything in C++11 or core boost that can help me here? Thanks a lot

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• Ensuring all waiting threads complete

  - by Daniel

  I'm building a system where the progress of calling threads is dependent on the state of two variables. One variable is updated sporadically by an external source (separate from the client threads) and multiple client threads block on a condition of both variables. The system is something like this TypeB waitForB() { // Can be called by many threads. synchronized (B) { while (A <= B) { B.wait(); } A = B; return B; { } void updateB(TypeB newB) { // Called by one thread. synchronized (B) { B.update(newB); B.notifyAll(); // All blocked threads must receive new B. } } I need all the blocked threads to receive the new value of B once it has been updated. But the problem is once a single thread finishes and updates A, the waiting condition becomes true again so some of the other threads become blocked and don't receive the new value of B. Is there a way of ensuring that only the last thread that was blocked on B updates A, or another way of getting this behaviour?

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• Callbacks on GUI Thread

  - by miguel

  We have an external data provider which, in its construtor, takes a callback thread for returning data upon. There are some issues in the system which I am suspicious are related to threading, however, in theory they cannot be, due to the fact that the callbacks should all be returned on the same thread. My question is, does code like this require thread synchronisation? class Foo { ExternalDataProvider _provider; public Foo() { // This is the c'tor for the xternal data provider, taking a callback loop as param _provider = new ExternalDataProvider(UILoop); _provider.DataArrived += ExternalProviderCallbackMethod; } public ExternalProviderCallbackMethod() { var itemArray[] = new String[4] { "item1", "item2", "item3", "item4" }; for (int i = 0; i < itemArray.Length; i++) { string s = itemArray[i]; switch(s) { case "item1": DoItem1Action(); break; case "item2": DoItem2Action(); break; default: DoDefaultAction(); break; } } } } The issue is that, very infrequently, DoItem2Action is executingwhen DoItem1Action should be exectuing. Is it at all possible threading is at fault here? In theory, as all callbacks are arriving on the same thread, they should be serialized, right? So there should be no need for thread sync here?

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• Is private method in spring service implement class thread safe

  - by Roger Ray

  I got a service in an project using Spring framework. public class MyServiceImpl implements IMyService { public MyObject foo(SomeObject obj) { MyObject myobj = this.mapToMyObject(obj); myobj.setLastUpdatedDate(new Date()); return myobj; } private MyObject mapToMyObject(SomeObject obj){ MyObject myojb = new MyObject(); ConvertUtils.register(new MyNullConvertor(), String.class); ConvertUtils.register(new StringConvertorForDateType(), Date.class); BeanUtils.copyProperties(myojb , obj); ConvertUtils.deregister(Date.class); return myojb; } } Then I got a class to call foo() in multi-thread; There goes the problem. In some of the threads, I got error when calling BeanUtils.copyProperties(myojb , obj); saying Cannot invoke com.my.MyObject.setStartDate - java.lang.ClassCastException@2da93171 obviously, this is caused by ConvertUtils.deregister(Date.class) which is supposed to be called after BeanUtils.copyProperties(myojb , obj);. It looks like one of the threads deregistered the Date class out while another thread was just about to call BeanUtils.copyProperties(myojb , obj);. So My question is how do I make the private method mapToMyObject() thread safe? Or simply make the BeanUtils thread safe when it's used in a private method. And will the problem still be there if I keep the code this way but instead I call this foo() method in sevlet? If many sevlets call at the same time, would this be a multi-thread case as well?

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• Task.wait not working as I imagined

  - by user2357446

  I am trying to download a file, wait for the file to finish downloading, and then read the file afterwards. I have the following methods to do this: private async Task startDownload(string link, string savePath) { WebClient client = new WebClient(); client.DownloadProgressChanged += new DownloadProgressChangedEventHandler(client_DownloadProgressChanged); client.DownloadFileCompleted += new AsyncCompletedEventHandler(client_DownloadFileCompleted); await client.DownloadFileTaskAsync(new Uri(link), savePath); } private void checkUpdateButton_Click(object sender, EventArgs e) { Task task = Task.Factory.StartNew(() => startDownload(versionLink, versionSaveTo)); task.Wait(); if (task.IsCompleted) { checkVersion(); } } The checkVersion() method reads the file that was downloaded. This is throwing an IOException saying that the file is in use by something else and cannot be read. I thought that having task.Wait would prevent the rest of the method from executing until the task was finished?

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• DispatcherOperations.Wait()

  - by Mark

  What happens if you call dispatcherOperation.Wait() on an operation that has already completed? Also, the docs say that it returns a DispatcherOperationStatus, but wouldn't that always be Completed since it (supposedly) doesn't return until it's done? I was trying to use it like this: private void Update() { while (ops.Count > 0) ops.Dequeue().Wait(); } public void Add(T item) { lock (sync) { if (dispatcher.CheckAccess()) { list.Add(item); OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, item)); } else { ops.Enqueue(dispatcher.BeginInvoke(new Action<T>(Add), item)); } } } I'm using this in WPF, so all the Add operations have to occur on the UI thread, but I figured I could basically just queue them up without having to wait for it to switch threads, and then just call Update() before any read operations to ensure that the list is up to date, but my program started hanging.

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• Why do debug symbols so adversely affect the performance of threaded applications on Linux?

  - by fluffels

  Hi. I'm writing a ray tracer. Recently, I added threading to the program to exploit the additional cores on my i5 Quad Core. In a weird turn of events the debug version of the application is now running slower, but the optimized build is running faster than before I added threading. I'm passing the "-g -pg" flags to gcc for the debug build and the "-O3" flag for the optimized build. Host system: Ubuntu Linux 10.4 AMD64. I know that debug symbols add significant overhead to the program, but the relative performance has always been maintained. I.e. a faster algorithm will always run faster in both debug and optimization builds. Any idea why I'm seeing this behavior?

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• Basic QT Event handling / Threading questions ?

  - by umanga

  Greetings , I am new to QT (4.6) and have some basic questions regarding its event mechanism.I come from Swing background so I am trying to compare it with QT. 1) Does Event-processing-loop run in seperate thread? (like EventDispatch thread in Swing) ? 2) If we open several 'QMainWindow' do they run in several threads? 3) Whats the best way to run an intensive process in a seperate thread? (like SwingWorker in Swing ? ) 4) If intesive-process runs in a seperate thread ,is it possible to call UI methods like update(),repaint() from that process? thanks in advance.

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• threading.Event wait function not signaled when subclassing Process class

  - by user1313404

  For following code never gets past the wait function in run. I'm certain I'm doing something ridiculously stupid, but since I'm not smart enough to figure out what, I'm asking. Any help is appreciated. Here is the code: import threading import multiprocessing from multiprocessing import Process class SomeClass(Process): def __init__(self): Process.__init__(self) self.event = threading.Event() self.event.clear() def continueExec(self): print multiprocessing.current_process().name print self print "Set:" + str(self.event.is_set()) self.event.set() print "Set:" + str(self.event.is_set()) def run(self): print "I'm running with it" print multiprocessing.current_process().name self.event.wait() print "I'm further than I was" print multiprocessing.current_process().name self.event.clear() def main(): s_list = [] for t in range(3): s = SomeClass() print "s:" + str(s) s_list.append(s) s.start() raw_input("Press enter to send signal") for t in range(3): print "s_list["+str(t)+"]:" + str(s_list[t]) s_list[t].continueExec() raw_input("Press enter to send signal") for t in range(3): s_list[t].join() print "All Done" if __name__ == "__main__": main()

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• Mouse move and thread

  - by bsebi

  When I move the mouse over the window, the program runs much faster (cc. 3 times). This is a real time webcam .Net/Mono application running on a MacBook. On Windows works perfect. Is this maybe a power saving function of the laptop? The code: Thread t = new Thread(Foo); t.Priority = ThreadPriority.Highest; // I've tried without priority too, doesn't matter t.Start(); ... void Foo() { while (true) { ++k; // then write k to the window somehow } }

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• ThreadExceptionEventHandler and invoking delegates

  - by QmunkE

  If I assign a ThreadExceptionEventHandler to Application.ThreadException, why when I invoke a delegate method using a control on the main application thread are any exceptions thrown by that delegate not triggering the event handler? i.e. static void Main() { ... Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(Application_ThreadException); Application.Run(new Form1()); } static void Application_ThreadException(object sender, System.Threading.ThreadExceptionEventArgs e) { Console.Error.Write("A thread exception occurred!"); } ... private void Form1_Load(object sender, EventArgs e) { Thread syncThread = new Thread(new ThreadStart(this.ThrowException)); syncThread.Start(); } private void ThrowException() { button1.Invoke(new MethodInvoker(delegate { // Not handled by ThreadExceptionEventHandler? throw new Exception(); })); } The context on this is that I have a background thread started from a form which is throwing an unhandled exception which terminates the application. I know this thread is going to be unreliable since it is network connectivity reliant and so subject to being terminated at any point, but I'm just interested as to why this scenario doesn't play out as I expect?

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• Physical Cores vs Virtual Cores in Parallelism

  - by Code Curiosity

  When it comes to virtualization, I have been deliberating on the relationship between the physical cores and the virtual cores, especially in how it effects applications employing parallelism. For example, in a VM scenario, if there are less physical cores than there are virtual cores, if that's possible, what's the effect or limits placed on the application's parallel processing? I'm asking, because in my environment, it's not disclosed as to what the physical architecture is. Is there still much advantage to parallelizing if the application lives on a dual core VM hosted on a single core physical machine?

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• Creating new process with Lua interpreater, failures in passing argumets

  - by user1131997

  I need help with passing arguments in CreateProcess() //Windows I want to: BOOL status = CreateProcess(L"C:\\Program Files (x86)\\Lua\\lua52.exe", NULL, NULL, NULL, FALSE, NULL, NULL, NULL, &si, &pi); But with passing some arguments.... Lua interpreater accepts file with lua-scripts, so I have prepared it and want to do: lua52 C:\1.lua for example... I have the path of some lua-script and want the interpreater of Lua to interpreate it and than get the result of program on Lua from Created process. I have tried in some ways to do it, but no success. Please, help! Thank you!

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• What's Wrong With My VB.NET Code Of Windows Forms Application?

  - by Krishanu Dey

  I've to forms frmPrint & frmEmail and a dataset(MyDataset) with some DataTable and DataTable Adapters. In frmPrint I've the following Sub Public Sub StartPrinting() try adapterLettersInSchedules.Fill(ds.LettersInSchedules) adapterLetters.Fill(ds.Letters) adapterClients.Fill(ds.Clients) adapterPrintJobs.GetPrintJobsDueToday(ds.PrintJobs, False, DateTime.Today) For Each prow As MyDataSet.PrintJobsRow In ds.PrintJobs Dim lisrow As MyDataSet.LettersInSchedulesRow = ds.LettersInSchedules.FindByID(prow.LetterInScheduleID) If lisrow.Isemail = False Then Dim clientrow As MyDataSet.ClientsRow = ds.Clients.FindByClientID(prow.ClientID) Dim letterrow As MyDataSet.LettersRow = ds.Letters.FindByID(lisrow.LetterID) 'prow. 'lisrow.is Label1.SuspendLayout() Label1.Refresh() Label1.Text = "Printing letter" txt.Rtf = letterrow.LetterContents txt.Rtf = txt.Rtf.Replace("<%Firstname%>", clientrow.FirstName) txt.Rtf = txt.Rtf.Replace("<%Lastname%>", clientrow.LastName) txt.Rtf = txt.Rtf.Replace("<%Title%>", clientrow.Title) txt.Rtf = txt.Rtf.Replace("<%Street%>", clientrow.Street) txt.Rtf = txt.Rtf.Replace("<%City%>", clientrow.City) txt.Rtf = txt.Rtf.Replace("<%State%>", clientrow.State) txt.Rtf = txt.Rtf.Replace("<%Zip%>", clientrow.Zip) txt.Rtf = txt.Rtf.Replace("<%PhoneH%>", clientrow.PhoneH) txt.Rtf = txt.Rtf.Replace("<%PhoneW%>", clientrow.PhoneW) txt.Rtf = txt.Rtf.Replace("<%Date%>", DateTime.Today.ToShortDateString) Try PDoc.PrinterSettings = printDlg.PrinterSettings PDoc.Print() prow.Printed = True adapterPrintJobs.Update(prow) Catch ex As Exception End Try End If Next prow ds.PrintJobs.Clear() Catch ex As Exception MessageBox.Show(ex.Message, "Print", MessageBoxButtons.OK, MessageBoxIcon.Error) End Try End Sub And in frmEmail i've the Following Sub Public Sub SendEmails() try adapterLettersInSchedules.Fill(ds.LettersInSchedules) adapterLetters.Fill(ds.Letters) adapterClients.Fill(ds.Clients) adapterEmailJobs.GetEmailJobsDueToday(ds.EmailJobs, False, Today) Dim ls_string As String For Each prow As MyDataSet.EmailJobsRow In ds.EmailJobs Dim lisrow As MyDataSet.LettersInSchedulesRow = ds.LettersInSchedules.FindByID(prow.LetterInScheduleID) If lisrow.Isemail = True Then Dim clientrow As MyDataSet.ClientsRow = ds.Clients.FindByClientID(prow.ClientID) Dim letterrow As MyDataSet.LettersRow = ds.Letters.FindByID(lisrow.LetterID) txt.Rtf = letterrow.LetterContents ls_string = RTF2HTML(txt.Rtf) ls_string = Mid(ls_string, 1, Len(ls_string) - 176) If ls_string = "" Then Throw New Exception("Rtf To HTML Conversion Failed") Label1.SuspendLayout() Label1.Refresh() Label1.Text = "Sending Email" If SendEmail(clientrow.Email, ls_string, letterrow.EmailSubject) Then Try prow.Emailed = True adapterEmailJobs.Update(prow) Catch ex As Exception End Try Else prow.Emailed = False adapterEmailJobs.Update(prow) End If End If Next prow Catch ex As Exception MessageBox.Show(ex.Message, "Email", MessageBoxButtons.OK, MessageBoxIcon.Error) End Try End Sub I'm running this two subs using two different Threads. Public th As New Thread(New ThreadStart(AddressOf StartFirstPrint)) Public th4 As New Thread(New ThreadStart(AddressOf sendFirstEmail)) Here is the code of StartFirstPrint and sendFirstEmail Public Sub StartFirstPrint() Do While thCont Try Dim frm As New frmPrint() 'frm.MdiParent = Me frm.StartPrinting() Catch ex As Exception End Try Loop End Sub Public Sub sendFirstEmail() Do While thCont Try Dim frmSNDEmail As New frmEmail frmSNDEmail.SendEmails() Catch ex As Exception End Try Loop End Sub the thCont is a public boolean variable that specifies when to shop those threads. Most Of the time this works very well. But some times it gives errors Like the following image I don't know why is this occurring. Please help me.

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• Neat way of calling InvokeRequired and BeginInvoke

  - by ho

  I seem to remember seeing some neat way of calling InvokeRequired and BeginInvoke to avoid repeating too much code in every event handler but I can't remember what that was. So does anyone know a neat way of writing that code?

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• Proper thread termination in multi-threaded C# application

  - by Brian

  I have what I think is a rather complex problem. I have a C# application that utilizes a plug-in architecture using reflection. The application loads plug-in dlls and the user is able to enable/disable them. When a plug-in is enabled, the main app starts a thread to run the plug-in in. In many cases the plug-in may have multiple threads of its own. When I want to disable a plug-in I am calling Thread.Abort(). This seems to kill the initial thread that was created for the plug-in, but any additional threads that the plug-in created continue running. Is there a better way to stop all of the associated plug-in's threads along with the main thread? Thanks.

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• multiple move operations and data processes in work thread

  - by younevertell

  main thread-- start workthread--StartStage(get list of positions for data process) -- move to one position -- data sampling*strong text*-- data collection--data analysis------data sampling*strong text* basically, work thread does the data sampling*strong text*-- data collection--data analysis------data sampling*strong text* loop for one positioin until press stop or target is obtained. my questions: After work thread finishs the loop for one positioin, it would end itself. now how to make the work thread moves to the next position to do the data process loop after work thread finish one position work, would not end itself until data process for all the positions are done? Thanks in advance!

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• Multiple things at once (Threads?)

  - by Jonathan

  All, What is a really simple way of having a program do more than one thing at once, even if the computer does not necessarily have multiple 'cores'. Can I do this by creating more than one Thread? My goal is to be able to have two computers networked (through Sockets) to respond to each-other's requests, while my program will at the same time be able to be managing a UI. I want the server to potentially handle more than one client at the same time as well. My understanding is that the communication is done with BufferedReader.readLine() and PrintWriter.println(). My problem is that I want the server to be waiting on multiple readLine() requests, and also be doing other things. How do I handle this? Many thanks, Jonathan

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• Thread safety in C# arrays

  - by Betamoo

  Does having 2 different threads : one reading from a C# array (e.g from first location), and another one writing to the same C# array but to a different location(e.g to the last location) is thread safe or not? (And I mean here without locking reading nor writing)

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• A member variable's hashCode() value is different

  - by Jacques René Mesrine

  There's a piece of code that looks like this. The problem is that during bootup, 2 initialization takes place. (1) Some method does a reflection on ForumRepository & performs a newInstance() purely to invoke #setCacheEngine. (2) Another method following that invokes #start(). I am noticing that the hashCode of the #cache member variable is different sometimes in some weird scenarios. Since only 1 piece of code invokes #setCacheEngine, how can the hashCode change during runtime (I am assuming that a different instance will have a different hashCode). Is there a bug here somewhere ? public class ForumRepository implements Cacheable { private static CacheEngine cache; private static ForumRepository instance; public void setCacheEngine(CacheEngine engine) { cache = engine; } public synchronized static void start() { instance = new ForumRepository(); } public synchronized static void addForum( ... ) { cache.add( .. ); System.out.println( cache.hashCode() ); // snipped } public synchronized static void getForum( ... ) { ... cache.get( .. ); System.out.println( cache.hashCode() ); // snipped } }

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