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• Please tell me what is wrong with my threading!!!

  - by kiddo

  I have a function where I will compress a bunch of files into a single compressed file..it is taking a long time(to compress),so I tried implementing threading in my application..Say if I have 20 files for compression,I separated that as 5*4=20,inorder to do that I have separate variables(which are used for compression) for all 4 threads in order to avoid locks and I will wait until the 4 thread finishes..Now..the threads are working but i see no improvement in their performance..normally it will take 1 min for 20 files(for example) after implementing threading ...there is only 5 or 3 sec difference., sometimes the same. here i will show the code for 1 thread(so it is for other3 threads) //main thread myClassObject->thread1 = AfxBeginThread((AFX_THREADPROC)MyThreadFunction1,myClassObject); .... HANDLE threadHandles[4]; threadHandles[0] = myClassObject->thread1->m_hThread; .... WaitForSingleObject(myClassObject->thread1->m_hThread,INFINITE); UINT MyThreadFunction(LPARAM lparam) { CMerger* myClassObject = (CMerger*)lparam; CString outputPath = myClassObject->compressedFilePath.GetAt(0);//contains the o/p path wchar_t* compressInputData[] = {myClassObject->thread1outPath, COMPRESS,(wchar_t*)(LPCTSTR)(outputPath)}; HINSTANCE loadmyDll; loadmydll = LoadLibrary(myClassObject->thread1outPath); fp_Decompress callCompressAction = NULL; int getCompressResult=0; myClassObject->MyCompressFunction(compressInputData,loadClient7zdll,callCompressAction,myClassObject->thread1outPath, getCompressResult,minIndex,myClassObject->firstThread,myClassObject); return 0; }

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• BlackBerry threading model

  - by Rory Fitzpatrick

  I've read a lot of comments mention in passing that the BlackBerry threading model deviates from the Java standard and can cause issues, but no amount of googling has enlightened me on what this means exactly. I've been developing a fairly large business application for the BlackBerry and, although I don't really have any previous experience with Java multi-threaded applications, haven't come across any issue that we've been able to blame on threading, other than what we caused ourselves. Can someone describe exactly how the BlackBerry threading model is different, and how I as a developer should take that into account? Obviously any links on the topic would also be great.

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• C# Threading in a method

  - by user177883

  I have the following method : public List<string> someMethod() { // populate list of strings // dump them to csv file //return to output } Question is: i dont want the user to wait for csv dump, which might take a while. If i use a thread for csvdump, will it complete? before or after the return of output?

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• Interrupt a thread in DatagramSocket.receive

  - by SEK

  I'm building an application that listens on both TCP and UDP, and I've run into some trouble with my shutdown mechanism. When I call Thread.interrupt() on each of the listening threads, the TCP thread is interrupted from listening, whereas the UDP listener isn't. To be specific, the TCP thread uses Socket.accept(), which simply returns (without actually connecting). Whereas the UDP thread uses DatagramSocket.receive, and doesn't exit that method. Is this an issue in my JRE, my OS, or should I just switch to (Datagram)Socket.close()?

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• passing variables when calling methon in new thread (iphone)

  - by Mouhamad Lamaa

  dear stacks i need to pass variables to the thread method when creating a new thread my code is the follwing //generating thread [NSThread detachNewThreadSelector:@selector(startThread) toTarget:self withObject:nil]; thread job - (void)startThread:(NSInteger *)var img:(UIImageView *) Img{ NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; [NSThread sleepForTimeInterval:var]; [self performSelectorOnMainThread:@selector(threadMethod) withObject:nil waitUntilDone:NO]; //i need to pass Img to threadMethod: [pool release]; } thread Method - (void)threadMethod:(UIImageView *) Img { //do some coding. } so how i can do this (pass parameter to both of methods

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• Can one thread open a socket and other thread close it?

  - by Pkp

  I have some kernel threads in Linux kernel, inside my KLM. I have a server thread, that listens to the channel, Once it sees there is an incoming connection, it creates an accept socket, accepts the connection and spawns a child thread. It also passes the accepted socket to the child kernel thread as the (void *) argument. The code is working fine. I had a design question. Suppose now the threads have to be terminated, main and the child threads, what would be the best way to close the accept socket. I can see two ways, 1] The main thread waits for all the child threads to exit, each of the child threads close the accept sockets while exiting, the last child thread passes a signal to the main thread for it to exit . Here even though the main thread was the one that created the accept socket, the child threads close that socket, and they do this before the main thread exits. So is this acceptable? Any problems you guys forsee here? 2] Second is the main thread closes all the accept sockets it created before it exits. But there may be a possibility(corner case) that the main thread gets an exception and will have to close, so if it closes the accept sockets before exiting, the child threads using that socket will be in danger. Hence i am using the first case i mentioned.Let me know what you guys think?

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• C: Making golbal static variables multithread safe

  - by giladsah

  I have global static variables in a C library, which generate exceptions in a multithread run. I need to make them safe in some way (i.e. - each thread should relate to a different instance of these variables). Any recommended methods? 10x

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• lock statement not working when there is a loop inside it?

  - by Ngu Soon Hui

  See this code: public class multiply { public Thread myThread; public int Counter { get; private set; } public string name { get; private set; } public void RunConsolePrint() { lock(this) { RunLockCode("lock"); } } private void RunLockCode(string lockCode) { Console.WriteLine("Now thread "+lockCode+" " + name + " has started"); for (int i = 1; i <= Counter; i++) { Console.WriteLine(lockCode+" "+name + ": count has reached " + i + ": total count is " + Counter); } Console.WriteLine("Thread " + lockCode + " " + name + " has finished"); } public multiply(string pname, int pCounter) { name = pname; Counter = pCounter; myThread = new Thread(new ThreadStart(RunConsolePrint)); } } And this is the test run code: static void Main(string[] args) { int counter = 50; multiply m2 = new multiply("Second", counter); multiply m1 = new multiply("First", counter); m1.myThread.Start(); m2.myThread.Start(); Console.ReadLine(); } I would expect that m2 must execute from start to finish before m1 starts executing, or vice versa, because of the lock statement. But the result I found was the call to lock first and lock second was intermingled together, i.e., something like this Now thread lock First has started Now thread lock Second has started lock First: Count has reached 1: total count is 50 lock First: Count has reached 2: total count is 50 lock Second: Count has reached 1: total count is 50 What did I do wrong?

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• What the best multi-thread application debugger for C++ apps.

  - by Coredumped

  I'm looking for a good multi-thread-aware debugger, capable of showing performance charts of application threads on Linux, don't know if such a thing exists, perhaps as a Eclipse plugin. The idea would be to track per thread memory allocation a CPU usage as well as being able to interrupt a thread and examine its stack trace, local vars, etc. It does not have to be an eclipse plugin or a free tool, do any of you have heard of something similar?

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• Is there a straightforward way to have a ThreadStatic instance member?

  - by Dan Tao

  With the ThreadStatic attribute I can have a static member of a class with one instance of the object per thread. This is really handy for achieving thread safety using types of objects that don't guarantee thread-safe instance methods (e.g., System.Random). It only works for static members, though. Is there some corresponding attribute that provides the same functionality, but for instance members? In other words, that allows me to have one instance of the object, per thread, per instance of the containing class?

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• How to identify deadlock conditions in a third-party application?

  - by Imhotep is Invisible

  I am using a third-party application to handle batch CD audio extraction via multiple FireWire attached devices, but the application frequently (though non-deterministically) hangs during the extraction. I suspect that the multithreaded application is deadlocking over some shared resource. The developer, however, suspects the problem lies elsewhere but is not addressing the problem at this time. I would like to be able to do some legwork on my end to a) prove the condition exists and b) ideally point him in the right direction. The problems: while I used to be a programmer, it's been awhile and I need to shake off the dust (last work I did was back in '99 and it was under Solaris, while the application runs under XP). Rather than there being a dearth of information online, there's almost too much to digest. Are there any suggested guides or tutorials that might help me get back up to speed sufficient enough to help identify and/or diagnose the deadlock, or are there tools or approaches that I should study up on to aid me in my task? Many thanks for all suggestions!

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• C++ thread to seperate process

  - by silverbandit91

  Is there any way i can have a thread branch off into it's own independent process? I know there's the CreateProcess function but as far as I can tell, you can only run external applications with it. Is what I'm asking for at all possible?

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• Start and run a class member function in background, in QT/C++

  - by Regof

  Once a minute I want to run a task, not blocking other GUI functions. I heared somthing about QConcurent::run ... Or should I use signals and slots?

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• Keeping track of threads when creating them recursively

  - by 66replica

  I'm currently working on some code for my Programming Languages course. I can't post the code but I'm permitted to talk about some high level concepts that I'm struggling with and receive input on them. Basically the code is a recursive DFS on a undirected graph that I'm supposed to convert to a concurrent program. My professor already specified that I should create my threads in the recursive DFS method and then join them in another method. Basically, I'm having trouble thinking of how I should keep track of the threads I'm creating so I can join all of them in the other method. I'm thinking an array of Threads but I'm unsure how to add each new thread to the array or even if that's the right direction.

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• ConcurrenctBag(Of MyType) Vs List(Of MyType)

  - by Ben

  What is the advantage of using a ConcurrentBag(Of MyType) against just using a List(Of MyType)? The MSDN page on the CB (http://msdn.microsoft.com/en-us/library/dd381779(v=VS.100).aspx) states that ConcurrentBag(Of T) is a thread-safe bag implementation, optimized for scenarios where the same thread will be both producing and consuming data stored in the bag So what is the advantage? I can understand the advantage of the other collection types in the Concurrency namespace, but this one puzzled me. Thanks.

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• C++ boost thread reusing threads

  - by aaa

  hi. I am trying to accomplish something like this: thread t; // create/initialize thread t.launch(); // launch thread. t.wait(); // wait t.launch(); // relaunch the same thread How to go about implementing something like this using boost threads? in essence, I need persistent relaunch-able thread. Thanks

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• What are all the concurrent things [data structure, algorithm, locking mechanism] missing in .Net 3.

  - by user49767

  First time I am bit disappointed in StackOverflow cause my http://stackoverflow.com/questions/2571727/c-concurrency-vs-java-concurrency-which-is-neatly-designed-which-is-better question was closed. My intension was just trying to gather knowledge from programming guru's who worked in both the programming technologies. Rather closing this question, please help me by discussing what is good, bad, and ugly in multi-threading part in both the platforms. It is also welcome, if someone would like to compare with .Net 4.0 with JDK 6 (or JDK 7)

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• Multi-threading does not work correctly using std::thread (C++ 11)

  - by user1364743

  I coded a small c++ program to try to understand how multi-threading works using std::thread. Here's the step of my program execution : Initialization of a 5x5 matrix of integers with a unique value '42' contained in the class 'Toto' (initialized in the main). I print the initialized 5x5 matrix. Declaration of std::vector of 5 threads. I attach all threads respectively with their task (threadTask method). Each thread will manipulate a std::vector<int> instance. I join all threads. I print the new state of my 5x5 matrix. Here's the output : 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 It should be : 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 42 0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 Here's the code sample : #include <iostream> #include <vector> #include <thread> class Toto { public: /* ** Initialize a 5x5 matrix with the 42 value. */ void initData(void) { for (int y = 0; y < 5; y++) { std::vector<int> vec; for (int x = 0; x < 5; x++) { vec.push_back(42); } this->m_data.push_back(vec); } } /* ** Display the whole matrix. */ void printData(void) const { for (int y = 0; y < 5; y++) { for (int x = 0; x < 5; x++) { printf("%d ", this->m_data[y][x]); } printf("\n"); } printf("\n"); } /* ** Function attached to the thread (thread task). ** Replace the original '42' value by another one. */ void threadTask(std::vector<int> &list, int value) { for (int x = 0; x < 5; x++) { list[x] = value; } } /* ** Return the m_data instance propertie. */ std::vector<std::vector<int> > &getData(void) { return (this->m_data); } private: std::vector<std::vector<int> > m_data; }; int main(void) { Toto toto; toto.initData(); toto.printData(); //Display the original 5x5 matrix (first display). std::vector<std::thread> threadList(5); //Initialization of vector of 5 threads. for (int i = 0; i < 5; i++) { //Threads initializationss std::vector<int> vec = toto.getData()[i]; //Get each sub-vectors. threadList.at(i) = std::thread(&Toto::threadTask, toto, vec, i); //Each thread will be attached to a specific vector. } for (int j = 0; j < 5; j++) { threadList.at(j).join(); } toto.printData(); //Second display. getchar(); return (0); } However, in the method threadTask, if I print the variable list[x], the output is correct. I think I can't print the correct data in the main because the printData() call is in the main thread and the display in the threadTask function is correct because the method is executed in its own thread (not the main one). It's strange, it means that all threads created in a parent processes can't modified the data in this parent processes ? I think I forget something in my code. I'm really lost. Does anyone can help me, please ? Thank a lot in advance for your help.

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• Look up values in a BDB for several files in parallel

  - by biznez

  What is the most efficient way to look up values in a BDB for several files in parallel? If I had a Perl script which did this for one file at a time, would forking/running the process in background with the ampersand in Linux work? How might Hadoop be used to solve this problem? Would threading be another solution?

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• Making global static variables multithread safe

  - by giladsah

  I have global static variables in a C library, which generate exceptions in a multithread run. I need to make them safe in some way (i.e., each thread should relate to a different instance of these variables). Any recommended methods?

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• Thread help with Android game

  - by Ciph3rzer0

  I need some help dealing with three Threads in Android One thread is the main thread, the other is the GLThread, and the other is a WorkerThread I created to update the game state. The problem I have is they all need to access the same LinkedList of game objects. Both the GLThread and my WorkerThread only read from the LinkedList, so no problem there, but occasionally I have the main thread adding in another game object to the list. How can I manage this? I tried using synchronized in front of the functions involved but it really slows down the application. For some reason, just catching the errors and not rendering or updating the game state that frame, causes it to start lagging permanently. Anyone have any great ideas?

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• Threading and iterating through changing collections

  - by adamjellyit

  In C# (console app) I want to hold a collection of objects. All objects are of same type. I want to iterate through the collection calling a method on each object. And then repeat the process continuously. However during iteration objects can be added or removed from the list. (The objects themselves will not be destroyed .. just removed from the list). Not sure what would happen with a foreach loop .. or other similar method. This has to have been done 1000 times before .. can you recommend a solid approach?

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• Android thread handler NullPointerException

  - by Realn0whereman

  So this null pointer is confusing me. I believe it is a scope issue. My main activity looks like this: public class App extends Activity { ProgressDialog progressDialog; ProgressThread progressThread; Then inside of the oncreate I do this: ProgressDialog progressDialog = new ProgressDialog(this); progressDialog.setProgressStyle(ProgressDialog.STYLE_SPINNER); progressDialog.setMessage("Fetching Images..."); ProgressThread progressThread = new ProgressThread(handler,mImageIds,mImages); progressThread.start(); progressDialog.show(); THEN inside progressThread which is a separate class I do mHandler.sendMessage(mHandler.obtainMessage()); Now up until this point i believe it behaves as it should. I have my handler hanging out in class scope right underneath my oncreate final Handler handler = new Handler() { public void handleMessage(Message msg){ progressDialog.hide(); progressThread.interrupt(); } }; The program thinks that progressDialog and progressThread are declared, but are null. Why would they be null if I instantiate in my oncreate.

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• C++ Win/Linux thread syncronization Event

  - by JP

  Hello I have some code that is cross-platform by unsing #ifdef OS, I have a Queue protected by a CriticalSection on Windows, and by a pthread_mutex_t on Linux. I would like to implement a Wait(timeout) call that would block a thread until something has been enqueued. I though about using WaitForSingleObject on windows but it don't seem to support CriticalSection. Which Win32 and which Linux functions should I use to Wait and Signal for a condition to happen. Thank

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• pthread_exit return value

  - by Manty

  This is surprising for me. void * thread_func(void *arg) { pthread_exit(&ret); } int main(void) { pthread_t thr; int *exit_status; pthread_create(&thr, NULL, thread_func, NULL); sleep(2); pthread_join(thr, (void **)&exit_status); printf("value of exit status - %d\n", *exit_status); ret = 20; pthread_join(thr, (void **)&exit_status); printf("value of exit status - %d\n", *exit_status); return 0; } The output is value of exit status - 50 value of exit status - 20 I was expecting both the times the exit_status would be the actual exit value(50 in my case) of the thread. Instead it is just returning the value of the global variable which I used for pthread_exit. Is it not a bug?

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