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  • Need help understanding .net ThreadPool

    - by Meredith
    I am trying to understand what ThreadPool does, I have this .NET example: class Program { static void Main() { int c = 2; // Use AutoResetEvent for thread management AutoResetEvent[] arr = new AutoResetEvent[50]; for (int i = 0; i < arr.Length; ++i) { arr[i] = new AutoResetEvent(false); } // Set the number of minimum threads ThreadPool.SetMinThreads(c, 4); // Enqueue 50 work items that run the code in this delegate function for (int i = 0; i < arr.Length; i++) { ThreadPool.QueueUserWorkItem(delegate(object o) { Thread.Sleep(100); arr[(int)o].Set(); // Signals completion }, i); } // Wait for all tasks to complete WaitHandle.WaitAll(arr); } } Does this run 50 "tasks", in groups of 2 (int c) until they all finish? Or I am not understanding what it really does.

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  • Asynchronous database update in Django?

    - by Mark
    I have a big form on my site. When the users fill it out and submit it, most of the data just gets dumped to the database, and then they get redirected to a new page. However, I'd also like to use the data to query another site, and then parse the results. That might take a bit longer. It's not essential that the user sees these results right away, so I was wondering if it's possible to asynchronously call a function that will handle this, and then return an HttpResponse from my view like usual without making them wait? If so... how? Any particular libraries I should look at?

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  • How to prevent the other threads from accessing a method when one thread is accessing a method?

    - by geeta
    I want to search for a string in 10 files and write the matching lines to a single file. I wrote the matching lines from each file to 10 output files(o/p file1,o/p file2...) and then copied those to a single file using 10 threads. But the output single file has mixed output(one line from o/p file1,another line from o/p file 2 etc...) because its accessed simultaneously by many threads. If I wait for all threads to complete and then write the single file it will be much slower. I want the output file to be written by one thread at a time. What should i do? My source code:(only writing to single file method) public void WriteSingle(File output_file,File final_output) throws IOException { synchronized(output_file){ System.out.println("Writing Single file"); FileOutputStream fo = new FileOutputStream(final_output,true); FileChannel fi = fo.getChannel(); FileInputStream fs = new FileInputStream(output_file); FileChannel fc = fs.getChannel(); int maxCount = (64 * 1024 * 1024) - (32 * 1024); long size = fc.size(); long position = 0; while (position < size) { position += fc.transferTo(position, maxCount, fi); } } }

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  • Clarification on Threads and Run Loops In Cocoa

    - by dubbeat
    I'm trying to learn about threading and I'm thoroughly confused. I'm sure all the answers are there in the apple docs but I just found it really hard to breakdown and digest. Maybe somebody could clear a thing or 2 up for me. 1)performSelectorOnMainThread Does the above simply register an event in the main run loop or is it somehow a new thread even though the method says "mainThread"? If the purpose of threads is to relieve processing on the main thread how does this help? 2) RunLoops Is it true that if I want to create a completely seperate thread I use "detachNewThreadSelector"? Does calling start on this initiate a default run loop for the thread that has been created? If so where do run loops come into it? 3) And Finally , I've seen examples using NSOperationQueue. Is it true to say that If you use performSelectorOnMainThread the threads are in a queue anyway so NSOperation is not needed? 4) Should I forget about all of this and just use the Grand Central Dispatch instead?

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  • Is there any class in the .NET Framework to represent a holding container for objects?

    - by Charles Prakash Dasari
    I am looking for a class that defines a holding structure for an object. The value for this object could be set at a later time than when this container is created. It is useful to pass such a structure in lambdas or in callback functions etc. Say: class HoldObject<T> { public T Value { get; set; } public bool IsValueSet(); public void WaitUntilHasValue(); } // and then we could use it like so ... HoldObject<byte[]> downloadedBytes = new HoldObject<byte[]>(); DownloadBytes("http://www.stackoverflow.com", sender => downloadedBytes.Value = sender.GetBytes()); It is rather easy to define this structure, but I am trying to see if one is available in FCL. I also want this to be an efficient structure that has all needed features like thread safety, efficient waiting etc. Any help is greatly appreciated.

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  • Caveats to be aware of when using threading in Python?

    - by knorv
    I'm quite new to threading in Python and have a couple of beginner questions. When starting more than say fifty threads using the Python threading module I start getting MemoryError. The threads themselves are very slim and not very memory hungry, so it seems like it is the overhead of the threading that causes the memory issues. Is there something I can do to increase the memory capacity or otherwise make Python allow for a larger number of threads? What is the maximum number of threads you've been able to run in your Python code using the threading module? Did you do any tricks to achieve that number? Are there any other caveats to be aware of when using the threading module?

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  • Is it multitasking?

    - by Newbie
    Consider the below program myThread = new Thread( new ThreadStart( delegate { Method1(); Method2(); } ) ); Is it that 2 threads are getting called parallely(multitasking) or a single thread is calling the methods sequentially? It's urgent.

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  • Thread synchronization and aborting.

    - by kubal5003
    Hello, I've got a little problem with ending the work of one of my threads. First things first so here's the app "layout": Thread 1 - worker thread (C++/CLI) - runs and terminates as expected for(...) { try { if(TabuStop) return; System::Threading::Monitor::Enter("Lock1"); //some work, unmanaged code } finally { if(stop) { System::Threading::Monitor::Pulse("Lock1"); } else { System::Threading::Monitor::Pulse("Lock1"); System::Threading::Monitor::Wait("Lock1"); } } } Thread 2 - display results thread (C#) while (WorkerThread.IsAlive) { lock ("Lock1") { if (TabuEngine.TabuStop) { Monitor.Pulse("Lock1"); } else { Dispatcher.BeginInvoke(RefreshAction); Monitor.Pulse("Lock1"); Monitor.Wait("Lock1", 5000); } } // Thread.Sleep(5000); } I'm trying to shut the whole thing down from app main thread like this: TabuEngine.TabuStop = true; //terminates nicely the worker thread and if (DisplayThread.IsAlive) { DisplayThread.Abort(); } I also tried using DisplayThread.Interrupt, but it always blocks on Monitor.Wait("Lock1", 5000); and I can't get rid of it. What is wrong here? How am I supposed to perform the synchronization and let it do the work that it is supposed to do? //edit I'm not even sure now if the trick with using "Lock1" string is really working and locks are placed on the same object..

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  • Various way to stop a thread - which is the correct way

    - by Yan Cheng CHEOK
    I had came across different suggestion of stopping a thread. May I know, which is the correct way? Or it depends? Using Thread Variable http://download.oracle.com/javase/1.4.2/docs/guide/misc/threadPrimitiveDeprecation.html private volatile Thread blinker; public void stop() { blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using boolean flag private volatile boolean flag; public void stop() { flag = false; } public void run() { while (flag) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } } Using Thread Variable together with interrupt private volatile Thread blinker; public void stop() { blinker.interrupt(); blinker = null; } public void run() { Thread thisThread = Thread.currentThread(); while (!thisThread.isInterrupted() && blinker == thisThread) { try { thisThread.sleep(interval); } catch (InterruptedException e){ } repaint(); } }

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  • Implement a threading to prevent UI block on a bug in an async function

    - by Marcx
    I think I ran up againt a bug in an async function... Precisely the getDirectoryListingAsync() of the File class... This method is supposted to return an object containing the lists of files in a specified folder. I found that calling this method on a direcory with a lot of files (in my tests more than 20k files), after few seconds there is a block on the UI until the process is completed... I think that this method is separated in two main block: 1) get the list of files 2) create the array with the details of the files The point 1 seems to be async (for a few second the ui is responsive), then when the process pass from point 1 to point 2 the block of the UI occurs until the complete event is dispathed... Here's some (simple) code: private function checkFiles(dir:File):void { if (dir.exists) { dir.addEventListener( FileListEvent.DIRECTORY_LISTING, listaImmaginiLocale); dir.getDirectoryListingAsync(); // after this point, for the firsts seconds the UI respond well (point 1), // few seconds later (point 2) the UI is frozen } } private function listaImmaginiLocale( event:FileListEvent ):void { // from this point on the UI is responsive again... } Actually in my projects there are some function that perform an heavy cpu usage and to prevent the UI block I implemented a simple function that after some iteration will wait giving time to UI to be refreshed. private var maxIteration:int = 150000; private function sampleFunct(offset:int = 0) :void { if (offset < maxIteration) { // do something // call the recursive function using a timeout.. // if the offset in multiple by 1000 the function will wait 15 millisec, // otherwise it will be called immediately // 1000 is a random number for the pourpose of this example, but I usually change the // value based on how much heavy is the function itself... setTimeout(function():void{aaa(++offset);}, (offset%1000?15:0)); } } Using this method I got a good responsive UI without afflicting performance... I'd like to implement it into the getDirectoryListingAsync method but I don't know if it's possibile how can I do it where is the file to edit or extend.. Any suggestion???

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  • Why does System.Threading.Timer callback successfully update UI?

    - by Geo P
    I have several System.Threading.Timers on my form application with callbacks that update the UI...successfully - i.e. without throwing errors. I had built these earlier, before I knew that UI should not be updated on any thread other than the UI thread. Now I am confused as to why it does not throw cross-thread exceptions when I am updating UI on these separate threading.timer threads? I will be changing these callbacks so that the UI updates are invoked on UI thread, but I am curious as to why this works. Edit: My application is a WinForms Application.

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  • Multithreaded Delegates/Events

    - by Matt
    I am trying to disable parts of the UI in a .NET app based on polling done on a background thread. The background thread checks to see if the global database connection the app uses is still open and operable. What I need to do, and would prefer to do it without polling on the UI thread, is to add an event handler that can be raised by the background thread if the connection status changes. That way, any form can have a handler that will disable those parts of the UI that require the connection to function. Attempting to use a straight event declaration in the class that holds the thread sub, and raising the event in the background thread causing cross-thread execution errors regarding accessing UI controls from other threads. Obviously, there is a correct way to do this, but we have limited experience with events (single threaded apps mainly), and almost none with delegates. I've read through documentation and examples for delegates, and it seems to be closer to what we need, but I'm not sure how to make it work in this instance. The app is written mainly in VB.NET, but an example or help in C# is fine too.

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  • Problems with Threading in Python 2.5, KeyError: 51, Help debugging?

    - by vignesh-k
    I have a python script which runs a particular script large number of times (for monte carlo purpose) and the way I have scripted it is that, I queue up the script the desired number of times it should be run then I spawn threads and each thread runs the script once and again when its done. Once the script in a particular thread is finished, the output is written to a file by accessing a lock (so my guess was that only one thread accesses the lock at a given time). Once the lock is released by one thread, the next thread accesses it and adds its output to the previously written file and rewrites it. I am not facing a problem when the number of iterations is small like 10 or 20 but when its large like 50 or 150, python returns a KeyError: 51 telling me element doesn't exist and the error it points out to is within the lock which puzzles me since only one thread should access the lock at once and I do not expect an error. This is the class I use: class errorclass(threading.Thread): def __init__(self, queue): self.__queue=queue threading.Thread.__init__(self) def run(self): while 1: item = self.__queue.get() if item is None: break result = myfunction() lock = threading.RLock() lock.acquire() ADD entries from current thread to entries in file and REWRITE FILE lock.release() queue = Queue.Queue() for i in range(threads): errorclass(queue).start() for i in range(desired iterations): queue.put(i) for i in range(threads): queue.put(None) Python returns with KeyError: 51 for large number of desired iterations during the adding/write file operation after lock access, I am wondering if this is the correct way to use the lock since every thread has a lock operation rather than every thread accessing a shared lock? What would be the way to rectify this?

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  • C++ - how does Sleep() and cin work?

    - by quano
    Just curious. How does actually the function Sleep() work (declared in windows.h)? Maybe not just that implementation, but anyone. With that I mean - how is it implemented? How can it make the code "stop" for a specific time? Also curious about how cin and those actually work. What do they do exactly? The only way I know how to "block" something from continuing to run is with a while loop, but considering that that takes a huge amount of processing power in comparison to what's happening when you're invoking methods to read from stdin (just compare a while (true) to a read from stdin), I'm guessing that isn't what they do.

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  • Explicit call of Runnable.run

    - by klaudio
    Hi, I have a question. Somebody, who was working on my code before me, created some method and passed Runnable as parameter, more likely: void myMethod(Runnable runnable){ runnable.run(); } Then calling myMethod out of main looks like: public static void main(String args[]) { try { myMethod(new Runnable(){ public void run() { //do something...; }}); } catch (Throwable t) { } } So, to supply parameter to myMethod I need to instantiate object of (in this case anonymous) class implementing Runnable. My question is: is it necessary to use Runnable in this example? Can I use any different interface? I mean I can create new interface with single method i.e. interface MyInterface{ void doThis(); } then change look of myMethod: void myMethod(MyInterface myObject){ myObject.doThis(); } And of course client too: public static void main(String args[]) { try { myMethod(new MyInterface (){ public void doThis() { //do something...; }}); } catch (Throwable t) { } } Or maybe something is about Runnable?!

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  • ReaderWriterLockSlim question.

    - by Kamarey
    There are lots written about the ReaderWriterLockSlim class which allows multiple read and a single write. All of these (at least that I had found) tell how to use it without much explanation why and how it works. The standard code sample is: lock.EnterUpgradeableReadLock(); try { if (test if write is required) { lock.EnterWriteLock(); try { change the resourse here. } finally { lock.ExitWriteLock(); } } } finally { lock.ExitUpgradeableReadLock(); } The question is: if upgradeable lock permits only a single thread to enter its section, why I should call EnterWriteLock method within? What will happen if I don't? Or what will happen if instead of EnterUpgradeableReadLock I will call EnterWriteLock and will write to a resource without using upgradeable lock at all?

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  • Using lock(obj) inside a recursive call

    - by Amby
    As per my understanding a lock is not released until the runtime completes the code block of the lock(obj) ( because when the block completes it calls Monitor.Exit(obj). With this understanding i am not able to understand the reason behind the behaviour of the following code. private static string obj = ""; private static void RecurseSome(int number) { Console.WriteLine(number); lock (obj) { RecurseSome(++number); } } //Call: RecurseSome(0) //Output: 0 1 2 3...... stack overflow exception There must be some concept that i am missing. Please help.

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  • Parallel software?

    - by mavric
    What is the meaning of "parallel software" and what are the differences between "parallel software" and "regular software"? What are its advantages and disadvantages? Does writing "parallel software" require a specific hardware or programming language ?

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  • Boost threading/mutexs, why does this work?

    - by Flamewires
    Code: #include <iostream> #include "stdafx.h" #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> using namespace std; boost::mutex mut; double results[10]; void doubler(int x) { //boost::mutex::scoped_lock lck(mut); results[x] = x*2; } int _tmain(int argc, _TCHAR* argv[]) { boost::thread_group thds; for (int x = 10; x>0; x--) { boost::thread *Thread = new boost::thread(&doubler, x); thds.add_thread(Thread); } thds.join_all(); for (int x = 0; x<10; x++) { cout << results[x] << endl; } return 0; } Output: 0 2 4 6 8 10 12 14 16 18 Press any key to continue . . . So...my question is why does this work(as far as i can tell, i ran it about 20 times), producing the above output, even with the locking commented out? I thought the general idea was: in each thread: calculate 2*x copy results to CPU register(s) store calculation in correct part of array copy results back to main(shared) memory I would think that under all but perfect conditions this would result in some part of the results array having 0 values. Is it only copying the required double of the array to a cpu register? Or is it just too short of a calculation to get preempted before it writes the result back to ram? Thanks.

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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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  • Invoking different methods on threads

    - by Kraken
    I have a main process main. It creates 10 threads (say) and then what i want to do is the following: while(required){ Thread t= new Thread(new ClassImplementingRunnable()); t.start(); counter++; } Now i have the list of these threads, and for each thread i want to do a set of process, same for all, hence i put that implementation in the run method of ClassImplementingRunnable. Now after the threads have done their execution, i wan to wait for all of them to stop, and then evoke them again, but this time i want to do them serially not in parallel. for this I join each thread, to wait for them to finish execution but after that i am not sure how to evoke them again and run that piece of code serially. Can i do something like for(each thread){ t.reevoke(); //how can i do that. t.doThis(); // Also where does `dothis()` go, given that my ClassImplementingRunnable is an inner class. } Also, i want to use the same thread, i.e. i want the to continue from where they left off, but in a serial manner. I am not sure how to go about the last piece of pseudo code. Kindly help. Working with with java.

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  • VB.NET Two different approaches to generic cross-threaded operations; which is better?

    - by BASnappl
    VB.NET 2010, .NET 4 Hello, I recently read about using SynchronizationContext objects to control the execution thread for some code. I have been using a generic subroutine to handle (possibly) cross-thread calls for things like updating UI controls that utilizes Invoke. I'm an amateur and have a hard time understanding the pros and cons of any particular approach. I am looking for some insight on which approach might be preferable and why. Update: This question is motivated, in part, by statements such as the following from the MSDN page on Control.InvokeRequired. An even better solution is to use the SynchronizationContext returned by SynchronizationContext rather than a control for cross-thread marshaling. Method 1: Public Sub InvokeControl(Of T As Control)(ByVal Control As T, ByVal Action As Action(Of T)) If Control.InvokeRequired Then Control.Invoke(New Action(Of T, Action(Of T))(AddressOf InvokeControl), New Object() {Control, Action}) Else Action(Control) End If End Sub Method 2: Public Sub UIAction(Of T As Control)(ByVal Control As T, ByVal Action As Action(Of Control)) SyncContext.Send(New Threading.SendOrPostCallback(Sub() Action(Control)), Nothing) End Sub Where SyncContext is a Threading.SynchronizationContext object defined in the constructor of my UI form: Public Sub New() InitializeComponent() SyncContext = WindowsFormsSynchronizationContext.Current End Sub Then, if I wanted to update a control (e.g., Label1) on the UI form, I would do: InvokeControl(Label1, Sub(x) x.Text = "hello") or UIAction(Label1, Sub(x) x.Text = "hello") So, what do y'all think? Is one way preferred or does it depend on the context? If you have the time, verbosity would be appreciated! Thanks in advance, Brian

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