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• java GC periodically enters into several full GC cycles

  - by Peter

  Environment: sun JDK 1.6.0_16 vm settings: -XX:+DisableExplicitGC -XX:+UseConcMarkSweepGC -Xms1024 -Xmx1024M -XX:MaxNewSize=448m -XX:NewSize=448m -XX:SurvivorRatio=4(6 also checked) -XX:MaxPermSize=128M OS: windows server 2003 processor: 4 cores of INTEL XEON 5130, 2000 Hz my application description: high intensity of concurrent(java 5 concurrency used) operations completed each time by commit to oracle. it's about 20-30 threads run non stop, doing tasks. application runs in JBOSS web container. My GC starts work normally, I see a lot of small GCs and all that time CPU shows good load, like all 4 cores loaded to 40-50%, CPU graph is stable. Then , after 1 min of good work, CPU starts drop to 0% on 2 cores from 4, it's graph becomes unstable, goes up and down("teeth"). I see, that my threads work slower(I have monitoring), I see that GC starts produce a lot of FULL GC during that time and next 4-5 minutes this situation remains as is, then for short period of time, like 1 minute, it gets back to normal situation, but shortly after that all bad thing repeats. Question: Why I have so frequent full GC??? How to prevent that? I played with SurvivorRatio - does not help. I noticed, that application behaves normally until first FULL GC occurs, while I have enough memory. Then it runs badly. my GC LOG: starts good then long period of FULL GCs(many of them) 1027.861: [GC 942200K-623526K(991232K), 0.0887588 secs] 1029.333: [GC 803279K(991232K), 0.0927470 secs] 1030.551: [GC 967485K-625549K(991232K), 0.0823024 secs] 1030.634: [GC 625957K(991232K), 0.0763656 secs] 1033.126: [GC 969613K-632963K(991232K), 0.0850611 secs] 1033.281: [GC 649899K(991232K), 0.0378358 secs] 1035.910: [GC 813948K(991232K), 0.3540375 secs] 1037.994: [GC 967729K-637198K(991232K), 0.0826042 secs] 1038.435: [GC 710309K(991232K), 0.1370703 secs] 1039.665: [GC 980494K-972462K(991232K), 0.6398589 secs] 1040.306: [Full GC 972462K-619643K(991232K), 3.7780597 secs] 1044.093: [GC 620103K(991232K), 0.0695221 secs] 1047.870: [Full GC 991231K-626514K(991232K), 3.8732457 secs] 1053.739: [GC 942140K(991232K), 0.5410483 secs] 1056.343: [Full GC 991232K-634157K(991232K), 3.9071443 secs] 1061.257: [GC 786274K(991232K), 0.3106603 secs] 1065.229: [Full GC 991232K-641617K(991232K), 3.9565638 secs] 1071.192: [GC 945999K(991232K), 0.5401515 secs] 1073.793: [Full GC 991231K-648045K(991232K), 3.9627814 secs] 1079.754: [GC 936641K(991232K), 0.5321197 secs]

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• HttpWebResponse get mixed up when used inside multiple threads

  - by Holli

  In my Application I have a few threads who will get data from a web service. Basically I just open an URL and get an XML output. I have a few threads who do this continuously but with different URLs. Sometimes the results are mixed up. The XML output doesn't belong to the URL of a thread but to the URL of another thread. In each thread I create an instance of the class GetWebPage and call the method Get from this instance. The method is very simple and based mostly on code from the MSDN documentation. (See below. I removed my error handling here!) public string Get(string userAgent, string url, string user, string pass, int timeout, int readwriteTimeout, WebHeaderCollection whc) { string buffer = string.Empty; HttpWebRequest myWebRequest = (HttpWebRequest)WebRequest.Create(url); if (!string.IsNullOrEmpty(userAgent)) myWebRequest.UserAgent = userAgent; myWebRequest.Timeout = timeout; myWebRequest.ReadWriteTimeout = readwriteTimeout; myWebRequest.Credentials = new NetworkCredential(user, pass); string[] headers = whc.AllKeys; foreach (string s in headers) { myWebRequest.Headers.Add(s, whc.Get(s)); } using (HttpWebResponse myWebResponse = (HttpWebResponse)myWebRequest.GetResponse()) { using (Stream ReceiveStream = myWebResponse.GetResponseStream()) { Encoding encode = Encoding.GetEncoding("utf-8"); StreamReader readStream = new StreamReader(ReceiveStream, encode); // Read 1024 characters at a time. Char[] read = new Char[1024]; int count = readStream.Read(read, 0, 1024); int break_counter = 0; while (count > 0 && break_counter < 10000) { String str = new String(read, 0, count); buffer += str; count = readStream.Read(read, 0, 1024); break_counter++; } } } return buffer; As you can see I have no public properties or any other shared resources. At least I don't see any. The url is the service I call in the internet and buffer is the XML Output from the server. Like I said I have multiple instances of this class/method in a few threads (10 to 12) and sometimes buffer does not belong the the url of the same thread but another thread.

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• Are indivisible operations still indivisible on multiprocessor and multicore systems?

  - by Steve314

  As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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• Exception calling remote SOAP call from thread

  - by Duncan

  This is an extension / next step of this question I asked a few minutes ago. I've a Delphi application with a main form and a thread. Every X seconds the thread makes a web services request for a remote object. It then posts back to the main form which handles updating the UI with the new information. I was previously using a TTimer object in my thread, and when the TTimer callback function ran, it ran in the context of the main thread (but the remote web services request did work). This rather defeated the purpose of the separate thread, and so I now have a simple loop and sleep routine in my thread's Execute function. The problem is, an exception is thrown when returning from GetIMySOAPService(). procedure TPollingThread.Execute; var SystemStatus : TCWRSystemStatus; begin while not Terminated do begin sleep(5000); try SystemStatus := GetIMySOAPService().GetSystemStatus; PostMessage( ParentHandle, Integer(apiSystemStatus), Integer(SystemStatus), 0 ); SystemStatus.DataContext := nil; LParam(SystemStatus) := 0; except end; end; end; Can anyone advise as to why this exception is being thrown when calling this function from the thread? I'm sure I'm overlooking something fundamental and simple. Thanks, Duncan

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• Why the performance of following code is degrading when I use threads ?

  - by DotNetBeginner

  Why the performance of following code is degrading when I use threads ? **1.Without threads int[] arr = new int[100000000]; //Array elements - [0][1][2][3]---[100000000-1] addWithOutThreading(arr); // Time required for this operation - 1.16 sec Definition for addWithOutThreading public void addWithOutThreading(int[] arr) { UInt64 result = 0; for (int i = 0; i < 100000000; i++) { result = result + Convert.ToUInt64(arr[i]); } Console.WriteLine("Addition = " + result.ToString()); } **2.With threads int[] arr = new int[100000000]; int part = (100000000 / 4); UInt64 res1 = 0, res2 = 0, res3 = 0, res4 = 0; ThreadStart starter1 = delegate { addWithThreading(arr, 0, part, ref res1); }; ThreadStart starter2 = delegate { addWithThreading(arr, part, part * 2, ref res2); }; ThreadStart starter3 = delegate { addWithThreading(arr, part * 2, part * 3, ref res3); }; ThreadStart starter4 = delegate { addWithThreading(arr, part * 3, part * 4, ref res4); }; Thread t1 = new Thread(starter1); Thread t2 = new Thread(starter2); Thread t3 = new Thread(starter3); Thread t4 = new Thread(starter4); t1.Start(); t2.Start(); t3.Start(); t4.Start(); t1.Join(); t2.Join(); t3.Join(); t4.Join(); Console.WriteLine("Addition = "+(res1+res2+res3+res4).ToString()); // Time required for this operation - 1.30 sec Definition for addWithThreading public void addWithThreading(int[] arr,int startIndex, int endIndex,ref UInt64 result) { for (int i = startIndex; i < endIndex; i++) { result = result + Convert.ToUInt64(arr[i]); } }

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• Printdialog in multithreaded wpf window thrown TargetInvocationException

  - by Nils

  I have designed a multithreaded app, which is starting most windows in an dedicated thread like this: Thread newWindowThread = new Thread(new ThreadStart(ThreadStartingPoint)); newWindowThread.SetApartmentState(ApartmentState.STA); newWindowThread.IsBackground = true; newWindowThread.Start(); However, if in one of those window-in-own-thread I try to print something by simply calling PrintDialog pDialog = new PrintDialog(); bool? doPrint = pDialog.ShowDialog(); I get a TargetInvocationException - it does look like the PrintDialog does not reside in the same thread as my window. Is there any way to create a thread-agnostic (or "thread-save") PrinterDialog ?

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• Catch a thread's exception in the caller thread in Python

  - by Mikee

  Hi Everyone, I'm very new to Python and multithreaded programming in general. Basically, I have a script that will copy files to another location. I would like this to be placed in another thread so I can output "...." to indicate that the script is still running. The problem that I am having is that if the files cannot be copied it will throw an exception. This is ok if running in the main thread; however, having the following code does not work: try: threadClass = TheThread(param1, param2, etc.) threadClass.start() ##### **Exception takes place here** except: print "Caught an exception" In the thread class itself, I tried to re-throw the exception, but it does not work. I have seen people on here ask similar questions, but they all seem to be doing something more specific than what I am trying to do (and I don't quite understand the solutions offered). I have seen people mention the usage of sys.exc_info(), however I do not know where or how to use it. All help is greatly appreciated! EDIT: The code for the thread class is below: class TheThread(threading.Thread): def __init__(self, sourceFolder, destFolder): threading.Thread.__init__(self) self.sourceFolder = sourceFolder self.destFolder = destFolder def run(self): try: shul.copytree(self.sourceFolder, self.destFolder) except: raise

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• Code runs 6 times slower with 2 threads than with 1

  - by Edward Bird

  So I have written some code to experiment with threads and do some testing. The code should create some numbers and then find the mean of those numbers. I think it is just easier to show you what I have so far. I was expecting with two threads that the code would run about 2 times as fast. Measuring it with a stopwatch I think it runs about 6 times slower! void findmean(std::vector<double>*, std::size_t, std::size_t, double*); int main(int argn, char** argv) { // Program entry point std::cout << "Generating data..." << std::endl; // Create a vector containing many variables std::vector<double> data; for(uint32_t i = 1; i <= 1024 * 1024 * 128; i ++) data.push_back(i); // Calculate mean using 1 core double mean = 0; std::cout << "Calculating mean, 1 Thread..." << std::endl; findmean(&data, 0, data.size(), &mean); mean /= (double)data.size(); // Print result std::cout << " Mean=" << mean << std::endl; // Repeat, using two threads std::vector<std::thread> thread; std::vector<double> result; result.push_back(0.0); result.push_back(0.0); std::cout << "Calculating mean, 2 Threads..." << std::endl; // Run threads uint32_t halfsize = data.size() / 2; uint32_t A = 0; uint32_t B, C, D; // Split the data into two blocks if(data.size() % 2 == 0) { B = C = D = halfsize; } else if(data.size() % 2 == 1) { B = C = halfsize; D = hsz + 1; } // Run with two threads thread.push_back(std::thread(findmean, &data, A, B, &(result[0]))); thread.push_back(std::thread(findmean, &data, C, D , &(result[1]))); // Join threads thread[0].join(); thread[1].join(); // Calculate result mean = result[0] + result[1]; mean /= (double)data.size(); // Print result std::cout << " Mean=" << mean << std::endl; // Return return EXIT_SUCCESS; } void findmean(std::vector<double>* datavec, std::size_t start, std::size_t length, double* result) { for(uint32_t i = 0; i < length; i ++) { *result += (*datavec).at(start + i); } } I don't think this code is exactly wonderful, if you could suggest ways of improving it then I would be grateful for that also.

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• Yet another C# Deadlock Debugging Question

  - by Roo

  Hi All, I have a multi-threaded application build in C# using VS2010 Professional. It's quite a large application and we've experienced the classing GUI cross-threading and deadlock issues before, but in the past month we've noticed the appears to lock up when left idle for around 20-30 minutes. The application is irresponsive and although it will repaint itself when other windows are dragged in front of the application and over it, the GUI still appears to be locked... interstingly (unlike if the GUI thread is being used for a considerable amount of time) the Close, Maximise and minimise buttons are also irresponsive and when clicked the little (Not Responding...) text is not displayed in the title of the application i.e. Windows still seems to think it's running fine. If I break/pause the application using the debugger, and view the threads that are running. There are 3 threads of our managed code that are running, and a few other worker threads whom the source code cannot be displayed for. The 3 threads that run are: The main/GUI thread A thread that loops indefinitely A thread that loops indefinitely If I step into threads 2 and 3, they appear to be looping correctly. They do not share locks (even with the main GUI thread) and they are not using the GUI thread at all. When stepping into the main/GUI thread however, it's broken on Application.Run... This problem screams deadlock to me, but what I don't understand is if it's deadlock, why can't I see the line of code the main/GUI thread is hanging on? Any help will be greatly appreciated! Let me know if you need more information... Cheers, Roo -----------------------------------------------------SOLUTION-------------------------------------------------- Okay, so the problem is now solved. Thanks to everyone for their suggestions! Much appreciated! I've marked the answer that solved my initial problem of determining where on the main/UI thread the application hangs (I handn't turned off the "Enable Just My Code" option). The overall issue I was experiencing was indeed Deadlock, however. After obtaining the call-stack and popping the top half of it into Google I came across this which explains exactly what I was experiencing... http://timl.net/ This references a lovely guide to debugging the issue... http://www.aaronlerch.com/blog/2008/12/15/debugging-ui/ This identified a control I was constructing off the GUI thread. I did know this, however, and was marshalling calls correctly, but what I didn't realise was that behind the scenes this Control was subscribing to an event or set of events that are triggered when e.g. a Windows session is unlocked or the screensaver exits. These calls are always made on the main/UI thread and were blocking when it saw the call was made on the incorrect thread. Kim explains in more detail here... http://krgreenlee.blogspot.com/2007/09/onuserpreferencechanged-hang.html In the end I found an alternative solution which did not require this Control off the main/UI thread. That appears to have solved the problem and the application no longer hangs. I hope this helps anyone who's confronted by a similar problem. Thanks again to everyone on here who helped! (and indirectly, the delightful bloggers I've referenced above!) Roo -----------------------------------------------------SOLUTION II-------------------------------------------------- Aren't threading issues delightful...you think you've solved it, and a month down the line it pops back up again. I still believe the solution above resolved an issue that would cause simillar behaviour, but we encountered the problem again. As we spent a while debugging this, I thought I'd update this question with our (hopefully) final solution: The problem appears to have been a bug in the Infragistics components in the WinForms 2010.1 release (no hot fixes). We had been running from around the time the freeze issue appeared (but had also added a bunch of other stuff too). After upgrading to WinForms 2010.3, we've yet to reproduce the issue (deja vu). See my question here for a bit more information: 'http://stackoverflow.com/questions/4077822/net-4-0-and-the-dreaded-onuserpreferencechanged-hang'. Hans has given a nice summary of the general issue. I hope this adds a little to the suggestions/information surrounding the nutorious OnUserPreferenceChanged Hang (or whatever you'd like to call it). Cheers, Roo

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• Accessing global variable in multithreaded Tomcat server

  - by jwegan

  I have a singleton object that I construct like thus: private static volatile KeyMapper mapper = null; public static KeyMapper getMapper() { if(mapper == null) { synchronized(Utils.class) { if(mapper == null) { mapper = new LocalMemoryMapper(); } } } return mapper; } The class KeyMapper is basically a synchronized wrapper to HashMap with only two functions, one to add a mapping and one to remove a mapping. When running in Tomcat 6.24 on my 32bit Windows machine everything works fine. However when running on a 64 bit Linux machine (CentOS 5.4 with OpenJDK 1.6.0-b09) I add one mapping and print out the size of the HashMap used by KeyMapper to verify the mapping got added (i.e. verify size = 1). Then I try to retrieve the mapping with another request and I keep getting null and when I checked the size of the HashMap it was 0. I'm confident the mapping isn't accidentally being removed since I've commented out all calls to remove (and I don't use clear or any other mutators, just get and put). The requests are going through Tomcat 6.24 (configured to use 200 threads with a minimum of 4 threads) and I passed -Xnoclassgc to the jvm to ensure the class isn't inadvertently getting garbage collected (jvm is also running in -server mode). I also added a finalize method to KeyMapper to print to stderr if it ever gets garbage collected to verify that it wasn't being garbage collected. I'm at my wits end and I can't figure out why one minute the entry in HashMap is there and the next it isn't :(

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• For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue?

  - by Jonathan Allen

  For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue? Concerns: * My goal is to pull up to 100 items at a time and send them as a batch to the next step. * If I use a ConcurrentQueue, I have to manually cause it to go asleep when there is no work to be done. Otherwise I waste CPU cycles on spinning. * If I use a BlockingQueue and I only have 99 work items, it could indefinitely block until there the 100th item arrives. http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx

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• C# : What if a static method is called from multiple threads?

  - by Holli

  In my Application I have a static method that is called from multiple threads at the same time. Is there any danger of my data being mixed up? In my first attempt the method was not static and I was creating multiple instance of the class. In that case my data got mixed up somehow. I am not sure how this happens because it only happens sometimes. I am still debugging. But now the method is static on I have no problems so far. Maybe it's just luck. I don't know for sure.

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• Can someone provide an easy explanation of how 'Full Fences' are implemented in .Net using Threading

  - by Kilhoffer

  I'm clear on the usage of MemoryBarrier, but not on what happens behind the scenes in the runtime. Can anyone give a good explanation of what goes on?

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• Why can't I use/cast an Action for/to a ThreadStart?

  - by Rookian

  Both are delegates and have the same signature, but I can not use Action as ThreadStart. Why? Action doIt; doIt = () => MyMethod("test"); Thread t; t = new Thread(doIt); t.Start(); but this seams to work: Thread t; t = new Thread(() => MyMethod("test")); t.Start();

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• how to create a system-wide independent universal counter object primarily for Database keys?

  - by andora

  I would like to create/use a system-wide independent universal 'counter object' that can be called via COM in a thread-safe manner. The counter object will be passed an ID to identify which counter to return, handle the counting, 'persist' the count (occasionally), have reasonable performance (as fast as possible) perhaps capable of 1000 counts per second or better (1mS) and be accessible cross-process/out-of-process. The current count status must be persisted between object restarts/shutdowns. The counter object is liklely to be a 'singleton' type object implemented in some form of free-threaded dictionary, containing maybe 10 counters (perhaps 50 max). The count needs to be monotonic and consistent, (ie: guaranteed unique sequential values). Each counter should have a few methods, like reset, inc, dec, set, clear, remove. As a luxury, I would like to have a variable-increment (ie: 'step by' value). To support thread-safefty, perhaps some sorm of critical-section or mutex call. It just needs to return a long/4byte signed integer. I really want something that can be called from anywhere, including VBScript, so I figure COM is my preferred solution. The primary use of this is for database keys. I am unable to use autoinc or guid type keys and have ruled out database-generated counting systems at this point. I've spent days researching this and I have really struggled to find a solution. The best I can find is a free-threaded dictionary object that can be instantiated using COM+ from Motobit - it seems to offer all the 'basics' and I guess I could create some form of wrapper for this. So, here are my questions: Does such a 'general purpose counter-object already exist? Can you direct me to it? (MS did do an IIS/ASP object called 'MSWC.Counter' but this isn't 'cross-process'/ out-of-process component and isn't thread-safe. (but if it was, it would do!) What is the best way of creating such a Component? (I'd prefer VB6 right-now, [don't ask!] but can do in VB.NET2005 if I had to). I don't have the skills/knowledge/tools to use anything else. I am desparate for a workable solution. I need specific guidance! If anybody can code something up for me I am prepared to pay for it.

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• Python - question regarding the concurrent use of `multiprocess`.

  - by orokusaki

  I want to use Python's multiprocessing to do concurrent processing without using locks (locks to me are the opposite of multiprocessing) because I want to build up multiple reports from different resources at the exact same time during a web request (normally takes about 3 seconds but with multiprocessing I can do it in .5 seconds). My problem is that, if I expose such a feature to the web and get 10 users pulling the same report at the same time, I suddenly have 60 interpreters open at the same time (which would crash the system). Is this just the common sense result of using multiprocessing, or is there a trick to get around this potential nightmare? Thanks

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• What is the JVM Scheduling algorithm ?

  - by IHawk

  Hello ! I am really curious about how does the JVM work with threads ! In my searches in internet, I found some material about RTSJ, but I don't know if it's the right directions for my answers. I also found this topic in sun's forums, http://forums.sun.com/thread.jspa?forumID=513&threadID=472453, but that's not satisfatory. Can someone give me some directions, material, articles or suggestion about the JVM scheduling algorithm ? I am also looking for information about the default configurations of Java threads in the scheduler, like 'how long does it take for every thread' in case of time-slicing. And this stuff. I would appreciate any help ! Thank you !

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• [F#] Parallelize code in nested loops

  - by Juliet

  You always hear that functional code is inherently easier to parallelize than non-functional code, so I decided to write a function which does the following: Given a input of strings, total up the number of unique characters for each string. So, given the input [ "aaaaa"; "bbb"; "ccccccc"; "abbbc" ], our method will returns a: 6; b: 6; c: 8. Here's what I've written: (* seq<#seq<char>> -> Map<char,int> *) let wordFrequency input = input |> Seq.fold (fun acc text -> (* This inner loop can be processed on its own thread *) text |> Seq.choose (fun char -> if Char.IsLetter char then Some(char) else None) |> Seq.fold (fun (acc : Map<_,_>) item -> match acc.TryFind(item) with | Some(count) -> acc.Add(item, count + 1) | None -> acc.Add(item, 1)) acc ) Map.empty This code is ideally parallelizable, because each string in input can be processed on its own thread. Its not as straightforward as it looks since the innerloop adds items to a Map shared between all of the inputs. I'd like the inner loop factored out into its own thread, and I don't want to use any mutable state. How would I re-write this function using an Async workflow?

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• How to implement wait(); to wait for a notifyAll(); from enter button?

  - by Dakota Miller

  Sorry for the confusion I posted the Worng Logcat info. I updated the question. I want to click Start to start a thread then when enter is clicked i want the thad to continue and get the message and handle the message in the thread then output it to the main thread and update the text view. How would i start a thread to wait for enter to be pressed and get the bundle for the Handler? Here is my Code: public class MainActivity extends Activity implements OnClickListener { Handler mHandler; Button enter; Button start; TextView display; String dateString; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); enter = (Button) findViewById(R.id.enter); start = (Button) findViewById(R.id.start); display = (TextView) findViewById(R.id.Display); enter.setOnClickListener(this); start.setOnClickListener(this); mHandler = new Handler() { <=============================This is Line 31 public void handleMessage(Message msg) { // TODO Auto-generated method stub super.handleMessage(msg); Bundle bundle = msg.getData(); String string = bundle.getString("outKey"); display.setText(string); } }; } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } @Override public void onClick(View v) { // TODO Auto-generated method stub switch (v.getId()) { case R.id.enter: Message msgin = Message.obtain(); Bundle bundlein = new Bundle(); String in = "It Works!"; bundlein.putString("inKey", in); msgin.setData(bundlein); notifyAll(); break; case R.id.start: new myThread().hello.start(); break; } } public class myThread extends Thread { Thread hello = new Thread() { @Override public void run() { // TODO Auto-generated method stub super.run(); Looper.prepare(); try { wait(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Handler Mhandler = new Handler() { @Override public void handleMessage(Message msg) { // TODO Auto-generated method stub super.handleMessage(msg); Bundle bundle = msg.getData(); dateString = bundle.getString("inKey"); } }; Looper.loop(); Message msg = Message.obtain(); Bundle bundle = new Bundle(); bundle.putString("outKey", dateString); msg.setData(bundle); mHandler.sendMessage(msg); } }; } } Here is the logcat info: 06-27 00:00:24.832: E/AndroidRuntime(18513): FATAL EXCEPTION: Thread-1210 06-27 00:00:24.832: E/AndroidRuntime(18513): java.lang.IllegalMonitorStateException: object not locked by thread before wait() 06-27 00:00:24.832: E/AndroidRuntime(18513): at java.lang.Object.wait(Native Method) 06-27 00:00:24.832: E/AndroidRuntime(18513): at java.lang.Object.wait(Object.java:364) 06-27 00:00:24.832: E/AndroidRuntime(18513): at com .example.learninghandlers.MainActivity$myThread$1.run(MainActivity.java:77)

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• Does my Dictionary must use locking mechanism?

  - by theateist

  Many threads have access to summary. Each thread will have an unique key for accessing the dictionary; Dictionary<string, List<Result>> summary; Do I need locking for following operations? summary[key] = new List<Result>() summary[key].Add(new Result()); It seems that I don't need locking because each thread will access dictionary with different key, but won't the (1) be problematic because of adding concurrently new record to dictionary with other treads?

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• WCF threading - non-responsive UI

  - by Sphynx

  Hi everyone. I'm trying to configure some WCF stuff. Currently, I have a server which allows remote users to download files, and client. In the server, I use a ServiceHost class. I assume it should be running on a separate thread, however, the server UI (WinForms) becomes locked when someone downloads a file. Is there a way to manage the WCF threading model? Thank you!

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• asp.net Background Threads Exception Handling

  - by Chris

  In my 3.5 .net web application I have a background thread that does a lot of work (the application is similar to mint.com in that it does a lot of account aggregation on background threads). I do extensive exception handling within the thread performing the aggregation but there's always the chance an unhandled exception will be thrown and my entire application will die. I've read some articles about this topic but they all seem fairly outdated and none of them implement a standard approach. Is there a standard approach to this nowadays? Is there any nicer way to handle this in ASP.NET 4.0?

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• Is Stream.Write thread-safe?

  - by Mike Spross

  I'm working on a client/server library for a legacy RPC implementation and was running into issues where the client would sometimes hang when waiting to a receive a response message to an RPC request message. It turns out the real problem was in my message framing code (I wasn't handling message boundaries correctly when reading data off the underlying NetworkStream), but it also made me suspicious of the code I was using to send data across the network, specifically in the case where the RPC server sends a large amount of data to a client as the result of a client RPC request. My send code uses a BinaryWriter to write a complete "message" to the underlying NetworkStream. The RPC protocol also implements a heartbeat algorithm, where the RPC server sends out PING messages every 15 seconds. The pings are sent out by a separate thread, so, at least in theory, a ping can be sent while the server is in the middle of streaming a large response back to a client. Suppose I have a Send method as follows, where stream is a NetworkStream: public void Send(Message message) { //Write the message to a temporary stream so we can send it all-at-once MemoryStream tempStream = new MemoryStream(); message.WriteToStream(tempStream); //Write the serialized message to the stream. //The BinaryWriter is a little redundant in this //simplified example, but here because //the production code uses it. byte[] data = tempStream.ToArray(); BinaryWriter bw = new BinaryWriter(stream); bw.Write(data, 0, data.Length); bw.Flush(); } So the question I have is, is the call to bw.Write (and by implication the call to the underlying Stream's Write method) atomic? That is, if a lengthy Write is still in progress on the sending thread, and the heartbeat thread kicks in and sends a PING message, will that thread block until the original Write call finishes, or do I have to add explicit synchronization to the Send method to prevent the two Send calls from clobbering the stream?

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• Java Thread Example ?

  - by JavaUser

  Hi, Anyone give example program which explains Java Threads in a simpler way.For example,we have the following threads t1 , t2 and t3 . Here I want code that shows each thread is executing simultaneously not sequentially like non-threaded java programs. Thx

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• What is the difference between a process and a thread

  - by James Fassett

  What is the technical difference between a process and a thread? I get the feeling a word like 'process' is over used and there is also hardware and software threads. How about light-weight processes in languages like Erlang? Is there a definitive reason to use one term over the other?

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