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  • C# Spawn Multiple Threads for work then wait until all finished

    - by pharoc
    just want some advice on "best practice" regarding multi-threading tasks. as an example, we have a C# application that upon startup reads data from various "type" table in our database and stores the information in a collection which we pass around the application. this prevents us from hitting the database each time this information is required. at the moment the application is reading data from 10 tables synchronously. i would really like to have the application read from each table in a different thread all running in parallel. the application would wait for all the threads to complete before continuing with the startup of the application. i have looked into BackGroundWorker but just want some advice on accomplishing the above. Does the method sound logical in order to speed up the startup time of our application How can we best handle all the threads keeping in mind that each thread's work is independent of one another, we just need to wait for all the threads to complete before continuing. i look forward to some answers

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  • Why should I use a thread vs using a process?

    - by danmine
    I'm a newbie at this so please forgive me for my ignorance. Separating different parts of a program into different processes seems (to me) to make a more elegant program then just threading everything. In what scenario would it make sense to make things run on a thread vs separating the program into different processes? When should I use a thread? Edit: Anything on how (or if) they act differently with single core and multi core would also be helpful.

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  • C++: is it safe to read an integer variable that's being concurrently modified without locking?

    - by Hongli
    Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect reads too? I've heard that there are some hardware architectures on which, if one thread modifies a variable, and another thread reads it, then the read result will be garbage; in this case I do need to protect reads. I've never seen such architectures though. This question assumes that a single transaction only consists of updating a single integer variable so I'm not worried about the states of any other variables that might also be involved in a transaction.

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  • Cocoa multhithreads, locks don't work

    - by Igor
    I have a threadMethod which shows in console robotMotorsStatus every 0.5 sec. But when I try to change robotMotorsStatus in changeRobotStatus method I receive an exception. Where I need to put locks in that program. #import "AppController.h" @implementation AppController extern char *robotMotorsStatus; - (IBAction)runThread:(id)sender { [self performSelectorInBackground:@selector(threadMethod) withObject:nil]; } - (void)threadMethod { char string_to_send[]="QFF001100\r"; //String prepared to the port sending (first inintialization) string_to_send[7] = robotMotorsStatus[0]; string_to_send[8] = robotMotorsStatus[1]; while(1){ [theLock lock]; usleep(500000); NSLog (@"Robot status %s", robotMotorsStatus); [theLock unlock]; } } - (IBAction)changeRobotStatus:(id)sender { robotMotorsStatus[0]='1'; }

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  • C++ WIN32: Short multitasking example

    - by Con Current
    I searched for examples on how to create a simple multithreaded app that does something similar to this: #include <iostream> using namespace std; int myConcurrentFunction( ) { while( 1 ) { cout << "b" << endl; } } int main( ) { // Start a new thread for myConcurrentFunction while( 1 ) { cout << "a" << endl; } } How can I get the above to output a and b "randomly" by starting a new thread instead of just calling myConcurrentFunction normally? I mean: What is the minimal code for it? Is it really only one function I have to call? What files do I need to include? I use MSVC 2010, Win32

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  • How do I best write my own background-working and communicatible (sending progress updates and getti

    - by Ivan
    I have to develop a class which can run it's own hard-coded task in a background thread and communicate with container class sending him progress updates and taking messages from it. I believe I am going to extend BackgroundWorker class but it looks a bit weird to extend and I haven't managed to find a good example wit Google. Can you share a link to a good example of solving such a task? Please don't offer placing a BackgroundWorker visually on a form and reading the standard tutorial, it's not for my case. Maybe I'd better not extend but encapsulate a BackgroundWorker, but I hardly understand how to use it outide WinForms designer either :-(

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  • Do I need to using locking against integers in c++ threads

    - by Shane MacLaughlin
    The title says it all really. If I am accessing a single integer type (e.g. long, int, bool, etc...) in multiple threads, do I need to use a synchronisation mechanism such as a mutex to lock them. My understanding is that as atomic types, I don't need to lock access to a single thread, but I see a lot of code out there that does use locking. Profiling such code shows that there is a significant performance hit for using locks, so I'd rather not. So if the item I'm accessing corresponds to a bus width integer (e.g. 4 bytes on a 32 bit processor) do I need to lock access to it when it is being used across multiple threads? Put another way, if thread A is writing to integer variable X at the same time as thread B is reading from the same variable, is it possible that thread B could end up a few bytes of the previous value mixed in with a few bytes of the value being written? Is this architecture dependent, e.g. ok for 4 byte integers on 32 bit systems but unsafe on 8 byte integers on 64 bit systems? Edit: Just saw this related post which helps a fair bit.

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  • VB.net SyncLock Object

    - by Budius
    I always seen on SyncLock examples people using Private Lock1 As New Object ' declaration SyncLock Lock1 ' usage but why? In my specific case I'm locking a Queue to avoid problems on mult-threading Enqueueing and Dequeueing my data. Can I lock the Queue object itself, like this? Private cmdQueue As New Queue(Of QueueItem) ' declaration SyncLock cmdQueue ' usage Any help appreciated. Thanks.

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  • Threads syncronization with ThreadPoolExecutor

    - by justme1
    I'm trying to implement some logic when I create main(father) thread witch executes several other threads. Then it waits for some condition which child threads creates. After condition is meet the father executes some more child threads. The problem that when I use wait/notify I have java.lang.IllegalMonitorStateException exception. Here is the code: public class MyExecutor { final static ArrayBlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(10); final static ExecutorService svc = Executors.newFixedThreadPool(1); static final ThreadPoolExecutor threadPool = new ThreadPoolExecutor(5, 8, 10, TimeUnit.SECONDS, queue); public static void main(String[] args) throws InterruptedException { final MyExecutor me = new MyExecutor(); svc.execute(new Runnable() { public void run() { try { System.out.println("Main Thread"); me.execute(threadPool, 1); System.out.println("Main Thread waiting"); wait(); System.out.println("Main Thread notified"); me.execute(threadPool, 2); Thread.sleep(100); threadPool.shutdown(); threadPool.awaitTermination(20000, TimeUnit.SECONDS); } catch (InterruptedException e) { e.printStackTrace(); } } }); svc.shutdown(); svc.awaitTermination(10000, TimeUnit.SECONDS); System.out.println("Main Thread finished"); } public void execute(ThreadPoolExecutor tpe, final int id) { tpe.execute(new Runnable() { public void run() { try { System.out.println("Child Thread " + id); Thread.sleep(2000); System.out.println("Child Thread " + id + " finished"); notify(); } catch (InterruptedException e) { e.printStackTrace(); } } }); } } When I comment wait and notify line I have the following output: Main Thread Main Thread waiting Main Thread notified Child Thread 1 Child Thread 2 Child Thread 1 finished Child Thread 2 finished Main Thread finished

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  • Lua operations, that works in mutitheaded environment

    - by SBKarr
    My application uses Lua in multithreaded environment with global mutex. It implemented like this: Thread locks mutex, Call lua_newthread Perform some initialization on coroutine Run lua_resume on coroutine Unlocks mutex lua_lock/unlock is not implemented, GC is stopped, when lua works with coroutine. My question is, can I perform steps 2 and 3 without locking, if initialisation process does not requires any global Lua structs? Can i perform all this process without locking at all, if coroutine does not requires globals too? In what case I generally can use Lua functions without locking?

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  • Can I have multiple instance of the mandlebrot example in one program?

    - by yan bellavance
    Basically what I did is I took the Mandlebrot example and have 3 instances of it in my program. So the program would look like a mainwindow that has 3 mandlebrot widgets in it, one besides the other. Is it possible that GDB doesnt support debugging multiple intances of a classe that derives from qthread or is it thread-unsafe to do so? I don't have any problems at run-time but when I put breakpoints in a function called by the QThread run() function I get a segmentation fault. I can clearly see that the function doesn't complete before returning to the breakpoint ie I the program stops at the breakpoint, I step into the lines of codes one by one but after a couple of instructions another thread startS using the function(even though they are different instances).

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  • Swing: How do I run a job from AWT thread, but after a window was layed out?

    - by java.is.for.desktop
    My complete GUI runs inside the AWT thread, because I start the main window using SwingUtilities.invokeAndWait(...). Now I have a JDialog which has just to display a JLabel, which indicates that a certain job is in progress, and close that dialog after the job was finished. The problem is: the label is not displayed. That job seems to be started before JDialog was fully layed-out. When I just let the dialog open without waiting for a job and closing, the label is displayed. The last thing the dialog does in its ctor is setVisible(true). Things such as revalidate(), repaint(), ... don't help either. Even when I start a thread for the monitored job, and wait for it using someThread.join() it doesn't help, because the current thread (which is the AWT thread) is blocked by join, I guess. Replacing JDialog with JFrame doesn't help either. So, is the concept wrong in general? Or can I manage it to do certain job after it is ensured that a JDialog (or JFrame) is fully layed-out? Simplified algorithm of what I'm trying to achieve: Create a subclass of JDialog Ensure that it and its contents are fully layed-out Start a process and wait for it to finish (threaded or not, doesn't matter) Close the dialog I managed to write a reproducible test case: EDIT Problem from an answer is now addressed: This use case does display the label, but it fails to close after the "simulated process", because of dialog's modality. import java.awt.*; import javax.swing.*; public class _DialogTest2 { public static void main(String[] args) throws Exception { SwingUtilities.invokeAndWait(new Runnable() { final JLabel jLabel = new JLabel("Please wait..."); @Override public void run() { JFrame myFrame = new JFrame("Main frame"); myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); myFrame.setSize(750, 500); myFrame.setLocationRelativeTo(null); myFrame.setVisible(true); JDialog d = new JDialog(myFrame, "I'm waiting"); d.setModalityType(Dialog.ModalityType.APPLICATION_MODAL); d.add(jLabel); d.setSize(300, 200); d.setLocationRelativeTo(null); d.setVisible(true); SwingUtilities.invokeLater(new Runnable() { @Override public void run() { try { Thread.sleep(3000); // simulate process jLabel.setText("Done"); } catch (InterruptedException ex) { } } }); d.setVisible(false); d.dispose(); myFrame.setVisible(false); myFrame.dispose(); } }); } }

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  • Is this a valid, lazy, thread-safe Singleton implementation for C#?

    - by Matthew
    I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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  • Why aren't my threads start at the same time? Java

    - by Ada
    Hi, I have variable number of threads which are used for parallel downloading. I used this, for(int i = 0; i< sth; i++){ thrList.add(new myThread (parameters)); thrList.get(i).start(); thrList.get(i).join(); } I don't know why but they wait for each other to complete. When using threads, I am supposed get mixed print outs, since right then there are several threads running that code. However, when I print them out, they are always in order and one thread waits for the previous one to finish first. I only want them to join the main thread, not wait for each other. I noticed that when I measured time while downloading in parallel. How can I fix this? Why are they doing it in order? In my .java, there is MyThread class with run and there is Downloader class with static methods and variables. Would they be the cause of this? The static methods and variables? How can I fix this problem?

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  • [Android] Thread Button sleep

    - by user557475
    Hello For my project,i´am trying to execute a Method every 10 seconds when i click a button "A" and it should stop when i click the button again (kind of on/off). this is what i reached :-/ : ButtonA.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Handler handler = new Handler(); handler.postDelayed(new Runnable() { public void run() { showCurrentLocation(); Methodexecute(); } }, 10000); } } }); how can i repeat executing this method every 10 seconds until the button is clicked again. thanks

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  • Delphi - Is there any equivalent to C# lock?

    - by CaldonCZE
    I'm writing a multi-threaded application in Delphi and need to use something to protect shared resources. In C# I'd use the "lock" keyword: private someMethod() { lock(mySharedObj) { //...do something with mySharedObj } } In Delphi I couldn't find anything similar, I found just TThread.Synchronize(someMethod) method, which prevents potential conflicts by calling someMethod in main VCL thread, but it isn't exactly what I want to do.... Edit: I'm using Delphi 6

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  • Turn based synchronization between threads

    - by Amarus
    I'm trying to find a way to synchronize multiple threads having the following conditions: * There are two types of threads: 1. A single "cyclic" thread executing an infinite loop to do cyclic calculations 2. Multiple short-lived threads not started by the main thread * The cyclic thread has a sleep duration between each cycle/loop iteration * The other threads are allowed execute during the inter-cycle sleep of the cyclic thread: - Any other thread that attempts to execute during an active cycle should be blocked - The cyclic thread will wait until all other threads that are already executing to be finished Here's a basic example of what I was thinking of doing: // Somewhere in the code: ManualResetEvent manualResetEvent = new ManualResetEvent(true); // Allow Externally call CountdownEvent countdownEvent = new CountdownEvent(1); // Can't AddCount a CountdownEvent with CurrentCount = 0 void ExternallyCalled() { manualResetEvent.WaitOne(); // Wait until CyclicCalculations is having its beauty sleep countdownEvent.AddCount(); // Notify CyclicCalculations that it should wait for this method call to finish before starting the next cycle Thread.Sleep(1000); // TODO: Replace with actual method logic countdownEvent.Signal(); // Notify CyclicCalculations that this call is finished } void CyclicCalculations() { while (!stopCyclicCalculations) { manualResetEvent.Reset(); // Block all incoming calls to ExternallyCalled from this point forward countdownEvent.Signal(); // Dirty workaround for the issue with AddCount and CurrentCount = 0 countdownEvent.Wait(); // Wait until all of the already executing calls to ExternallyCalled are finished countdownEvent.Reset(); // Reset the CountdownEvent for next cycle. Thread.Sleep(2000); // TODO: Replace with actual method logic manualResetEvent.Set(); // Unblock all threads executing ExternallyCalled Thread.Sleep(1000); // Inter-cycles delay } } Obviously, this doesn't work. There's no guarantee that there won't be any threads executing ExternallyCalled that are in between manualResetEvent.WaitOne(); and countdownEvent.AddCount(); at the time the main thread gets released by the CountdownEvent. I can't figure out a simple way of doing what I'm after, and almost everything that I've found after a lengthy search is related to producer/consumer synchronization which I can't apply here.

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  • executorservice to read data from database in chuncks and run process on them

    - by TazMan
    I'm trying to write a process that would read data from a database and upload it onto a cloud datastore. How can I decide the partition strategy of the data? I want to query the table in chunks and process each chunk in 10 threads. Each thread basically will send the data to an individual node on a 10 node cluster on the cloud.. Where in the below multi threading code will the dataquery to extract and send 10 concurrent requests for uploading data to cloud would be? public class Caller { public static void main(String[] args) { ExecutorService executor = Executors.newFixedThreadPool(10); for (int i = 0; i < 10; i++) { Runnable worker = new DomainCDCProcessor(i); executor.execute(worker); } executor.shutdown(); while (!executor.isTerminated()) { } System.out.println("Finished all threads"); } }

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  • Thread is being killed by the OS

    - by Or.Ron
    I'm currently programming an app that extracts frames from a movie clip. I designed it so that the extraction will be done on a separate thread to prevent the application from freezing. The extraction process itself is taking a lot of resources, but works fine when used in the simulator. However, there are problems when building it for the iPad. When I perform another action (I'm telling my AV player to play while I extract frames), the thread unexpectedly stops working, and I believe it's being killed. I assume it's becauase I'm using a lot of resources, but not entirely sure. Here are my questions: 1. How can I tell if/why my thread stopping? 2. If it's really from over processing what should I do? I really need this action to be implemented. Heres some code im using: To create the thread: [NSThread detachNewThreadSelector:@selector(startReading) toTarget:self withObject:nil]; I'll post any information you need, Thanks so much! Update I'm using GCD now and it populates the threads for me. However the OS still kills the threads. I know exactly when is it happening. when i tell my [AVplayer play]; it kills the thread. This issue is only happening in the actual iPad and not on the simulator

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  • Thread Code...anything wrong with this, must use java 1.4

    - by bmw0128
    I have a servlet automatically firing up when the app server starts, and in its init(), I'm making another thread: init(){ new FooThread() } in FooThread(), i want to periodically check the status of a DB value, then depending on the value, make a web service call. When these two tasks complete, I want the thread to sleep to wait a certain period then repeat. This cycle would just continue forever. FooThread: public class FooThread implements Runnable{ Thread t; FooThread(){ t = new Thread(this, "BBSThread"); logger.info("*** about to start " + t.getName()); t.start(); logger.info("*** started: " + t); } public void run() { try{ while(true){ //do the db check, then conditionally do the web services call logger.info("*** calling sleep() ***"); Thread.sleep(50000); logger.info("*** now awake ***"); } } catch (InterruptedException e) { System.out.println("*** FooThread interrupted"); } } }

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  • Threaded Python port scanner

    - by Amnite
    I am having issues with a port scanner I'm editing to use threads. This is the basics for the original code: for i in range(0, 2000): s = socket(AF_INET, SOCK_STREAM) result = s.connect_ex((TargetIP, i)) if(result == 0) : c = "Port %d: OPEN\n" % (i,) s.close() This takes approx 33 minutes to complete. So I thought I'd thread it to make it run a little faster. This is my first threading project so it's nothing too extreme, but I've ran the following code for about an hour and get no exceptions yet no output. Am I just doing the threading wrong or what? import threading from socket import * import time a = 0 b = 0 c = "" d = "" def ScanLow(): global a global c for i in range(0, 1000): s = socket(AF_INET, SOCK_STREAM) result = s.connect_ex((TargetIP, i)) if(result == 0) : c = "Port %d: OPEN\n" % (i,) s.close() a += 1 def ScanHigh(): global b global d for i in range(1001, 2000): s = socket(AF_INET, SOCK_STREAM) result = s.connect_ex((TargetIP, i)) if(result == 0) : d = "Port %d: OPEN\n" % (i,) s.close() b += 1 Target = raw_input("Enter Host To Scan:") TargetIP = gethostbyname(Target) print "Start Scan On Host ", TargetIP Start = time.time() threading.Thread(target = ScanLow).start() threading.Thread(target = ScanHigh).start() e = a + b while e < 2000: f = raw_input() End = time.time() - Start print c print d print End g = raw_input()

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  • Qt: How to use QTimer to print a message to a QTextBrowser every 10 seconds?

    - by Aaron McKellar
    Hello, I have working at this for hours and cannot figure it out nor can I find any help online that works. Basically the gist of what I am trying to accomplish is to have a Qt GUI with a button and a QTextBrowser. When I push the button I want it to diplay a message and then keep printing this message every 10 seconds. I figured I would use QTimer because it makes sense to have a timer to diplay the message every 10 seconds. When I originally implemented this into my buttonClicked() SLOT it caused the program to freeze. I looked online for a solution and found QApplication::processEvents(). So basically in my function I had something like this: while(1) { QTimer *timer; connect(...) //omitted parameters for this example timer.start(10000); ui->diplay->append("Message"); while(timer.isActive()) { QApplication::processEvents() } } I figured it would break out of the timer.isActive() while loop but it won't it simply stays in there. So I figured this is a threading issue. So I figured out how to use QThreads but I still can't get it to work. Basically when I create a thread with a timer on it and the thread tells the timer to start, the program closes and the console says "The program has unexpectedly finished". There has to be an easy way to do this but my track record with Qt has always been that th

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  • Does async and await incease performance of an ASP.Net application

    - by Kerezo
    I recently read a article about c#-5 and new $ nice asynchronous programming. I see it works greate in windows application. The question came to me before is if this feature can increase ASP.Net performance? consider this code: public T GetData() { var d = GetSomeData(); return d; } and public async T GetData2() { var d = await GetSomeData(); return d; } Has in an ASP.Net appication that two codes difference? thanks

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