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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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  • 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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  • Windows App. Thread Aborting Issue

    - by Patrick
    I'm working on an application that has to make specific decisions based on files that are placed into a folder being watched by a file watcher. Part of this decision making process involves renaming files before moving them off to another folder to be processed. Since I'm working with files of all different sizes I created an object that checks the file in a seperate thread to verify that it is "available" and when it is it fires an event. When I run the rename code from inside this available event it works. public void RenameFile_Test() { string psFilePath = @"C:\File1.xlsx"; tgt_File target = new FileObject(psFilePath); target.FileAvailable += new FileEventHandler(OnFileAvailable); target.FileUnAvailable += new FileEventHandler(OnFileUnavailable); } private void OnFileAvailable(object source, FileEventArgs e) { ((FileObject)source).RenameFile(@"C:\File2.xlsx"); } The problem I'm running into is that when the extensions are different from the source file and the rename to file I am making a call to a conversion factory that returns a factory object based on the type of conversion and then converts the file accordingly before doing the rename. When I run that particular piece of code in unit test it works, the factory object is returned, and the conversion happens correctly. But when I run it within the process I get up to the... moExcelApp = new Application(); part of converting an .xls or .xlsx to a .csv and i get a "Thread was being Aborted" error. Any thoughts? Update: There is a bit more information and a bit of map of how the application works currently. Client Application running FSW On File Created event Creates a FileObject passing in the path of the file. On construction the file is validated: if file exists is true then, Thread toAvailableCheck = new Thread(new ThreadStart(AvailableCheck)); toAvailableCheck.Start(); The AvailableCheck Method repeatedly tries to open a streamreader to the file until the reader is either created or the number of attempts times out. If the reader is opened, it fires the FileAvailable event, if not it fires the FileUnAvailable event, passing back itself in the event. The client application is wired to catch those events from inside the Oncreated event of the FSW. the OnFileAvailable method then calls the rename functionality which contains the excel interop call. If the file is being renamed (not converted, extensions stay the same) it does a move to change the name from the old file name to the new, and if its a conversion it runs a conversion factory object which returns the correct type of conversion based on the extensions of the source file and the destination file name. If it is a simple rename it works w/o a problem. If its a conversion (which is the XLS to CSV object that is returned as a part of the factory) the very first thing it does is create a new application object. That is where the application bombs. When i test the factory and conversion/rename process outside of the thread and in its own unit test the process works w/o a problem. Update: I tested the Excel Interop inside a thread by doing this: [TestMethod()] public void ExcelInteropTest() { Thread toExcelInteropThreadTest = new Thread(new ThreadStart(Instantiate_App)); toExcelInteropThreadTest.Start(); } private void Instantiate_App() { Application moExcelApp = new Application(); moExcelApp.Quit(); } And on the line where the application is instatntiated I got the 'A first chance exception of type 'System.Threading.ThreadAbortException' error. So I added; toExcelInteropThreadTest.SetApartmentState(ApartmentState.MTA); after the thread instantiation and before the thread start call and still got the same error. I'm getting the notion that I'm going to have to reconsider the design.

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  • How solve consumer/producer task using semaphores

    - by user1074896
    I have SimpleProducerConsumer class that illustrate consumer/producer problem (I am not sure that it's correct). public class SimpleProducerConsumer { private Stack<Object> stack = new Stack<Object>(); private static final int STACK_MAX_SIZE = 10; public static void main(String[] args) { SimpleProducerConsumer pc = new SimpleProducerConsumer(); new Thread(pc.new Producer(), "p1").start(); new Thread(pc.new Producer(), "p2").start(); new Thread(pc.new Consumer(), "c1").start(); new Thread(pc.new Consumer(), "c2").start(); new Thread(pc.new Consumer(), "c3").start(); } public synchronized void push(Object d) { while (stack.size() >= STACK_MAX_SIZE) try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } stack.push(new Object()); System.out.println("push " + Thread.currentThread().getName() + " " + stack.size()); notify(); } public synchronized Object pop() { while (stack.size() == 0) try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } try { Thread.sleep(50); } catch (InterruptedException e) { e.printStackTrace(); } stack.pop(); System.out.println("pop " + Thread.currentThread().getName() + " " + stack.size()); notify(); return null; } class Consumer implements Runnable { @Override public void run() { while (true) { pop(); } } } class Producer implements Runnable { @Override public void run() { while (true) { push(new Object()); } } } } I found simple realization of semaphore(here:http://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html I know that there is concurrency package) How I need to change code to exchange java objects monitors to my custom semaphore. (To illustrate C/P problem using semaphores) Semaphore: class Semaphore { private int counter; public Semaphore() { this(0); } public Semaphore(int i) { if (i < 0) throw new IllegalArgumentException(i + " < 0"); counter = i; } public synchronized void release() { if (counter == 0) { notify(); } counter++; } public synchronized void acquire() throws InterruptedException { while (counter == 0) { wait(); } counter--; } }

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  • Thread in android

    - by ravi adhikari
    Hi experts, I need some help as i am just calling a method in a thread. now what i want is wait for reply form getData() method only for 15 seconds. If it reply before 15 seconds it should be terminated otherwise after 15 seconds it should be terminated. The code is given below: boolean networkStatus; private Runnable runnable; private ProgressDialog m_ProgressDialog = null; private Runnable returnRes = new Runnable() { @Override public void run() { if(networkStatus){ setData(); m_ProgressDialog.dismiss(); } }; private void callGetdata(){ runnable = new Runnable() { @Override public void run() { networkStatus = getData(); runOnUiThread(returnRes); } }; Thread thread = new Thread(null, runnable, "MovetoBackground"); thread.start(); m_ProgressDialog = ProgressDialog.show(this, "", getString(R.string.loadMsg), true); }

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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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  • 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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  • Is this use of PreparedStatements in a Thread in JAVA correct?

    - by Gormcito
    I'm still an undergrad just working part time and so I'm always trying to be aware of better ways to do things. Recently I had to write a program for work where the main thread of the program would spawn "task" threads (for each db "task" record) which would perform some operations and then update the record to say that it has finished. Therefore I needed a database connection object and PreparedStatement objects in or available to the ThreadedTask objects. This is roughly what I ended up writing, is creating a PreparedStatement object per thread a waste? I thought static PreparedStatments could create race conditions... Thread A stmt.setInt(); Thread B stmt.setInt(); Thread A stmt.execute(); Thread B stmt.execute(); A´s version never gets execed.. Is this thread safe? Is creating and destroying PreparedStatement objects that are always the same not a huge waste? public class ThreadedTask implements runnable { private final PreparedStatement taskCompleteStmt; public ThreadedTask() { //... taskCompleteStmt = Main.db.prepareStatement(...); } public run() { //... taskCompleteStmt.executeUpdate(); } } public class Main { public static final db = DriverManager.getConnection(...); }

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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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  • .NET: Start a thread as suspended

    - by Ikaso
    In unmanaged code you can create a thread in suspended state. In .NET Framework I can't find this option. Is it because the Thread constructor puts the thread in a suspended state? Is there other reasons why this is not supported?

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  • LINQ Changeset multi-threading

    - by Xodarap
    I'm using LINQ to SQL and after I submit some changes I want to spawn a thread which looks through all the changes and updates our lucene index as necessary. My code looks vaguely like: (new Thread(() => { UpdateIndex(context.GetChangeSet()); }).Start(); Sometimes though I get an InvalidOperationException, which I think is because context.GetChangeSet() is not thread-safe, and so if the change set is modified in one thread while another thread is enumerating through it, problems arise. Is there a "thread-safe" version of GetChangeSet()? Or some way I can do ChangeSet.clone() or something?

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  • Limiting object allocation over multiple threads

    - by John
    I have an application which retrieves and caches the results of a clients query. The client then requests different chunks of data and the application sends the relevant results and removes them from the cache. A new requirement for this application is that there needs to be a run-time configurable maximum number of results which may be cached. I've taken the naive approach and implemented this by using a counter under a lock which is incremented every time a result is cached and decremented whenever a result is removed from the cache. Unfortunately, this has drastically reduced the applications performance when processing a large number of concurrent requests. I have tried both a critical section lock and spin-lock; the performance improves a bit with a spin-lock, but is still unacceptably slow. Is there a better way to solve this problem which may improve performance? Right now I have a thread pool that services requests and each request is tied to a Request object which stores that cached results for that particular request. Here is a simplified pseudo code version of my current implementation: void ResultCallback( Result result, Request *request ) { lock totalResultsCached lock cachedLimit if( totalResultsCached + 1 > cachedLimit ) { unlock cachedLimit unlock totalResultsCached //cancel the request return; } ++totalResultsCached; unlock cachedLimit unlock totalResultsCached request.add(result) } void SendResults( int resultsToSend, Request *request ) { while ( resultsToSend > 0 ) { send(request.remove()) lock totalResultsCached --totalResultsCached unlock totalResultsCached --resultsToSend; } }

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  • How to implement a multi-threaded asynchronous operation?

    - by drowneath
    Here's how my current approach looks like: // Somewhere in a UI class // Called when a button called "Start" clicked MyWindow::OnStartClicked(Event &sender) { _thread = new boost::thread(boost::bind(&MyWindow::WorkToDo, this)); } MyWindow::WorkToDo() { for(int i = 1; i < 10000000; i++) { int percentage = (int)((float)i / 100000000.f); _progressBar->SetValue(percentage); _statusText->SetText("Working... %d%%", percentage); printf("Pretend to do something useful...\n"); } } // Called on every frame MyWindow::OnUpdate() { if(_thread != 0 && _thread->timed_join(boost::posix_time::seconds(0)) { _progressBar->SetValue(100); _statusText->SetText("Completed!"); delete _thread; _thread = 0; } } But I'm afraid this is far from safe since I keep getting unhandled exception at the end of the program execution. I basically want to separate a heavy task into another thread without blocking the GUI part.

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  • Threadpool with pasistant worker instances

    - by Matt Smokey-waters Holmes
    So basically what im trying to do is queue up tasks in a thread pool to be executed as soon as a worker becomes free, i have found various examples of this but in all cases the examples have been setup to use a new Worker instance for each job, i want persistent workers. Im trying to make a ftp backup tool, i have it working but because of the limitations of a single connection it is slow. What i ideally want to do is have a single connection for scanning directories and building up a file list then four workers to download said files. Here is an example of my worker /** * FTP Worker */ public class Worker implements Runnable { protected FTPClient _ftp; // Connection details protected String _host = ""; protected String _user = ""; protected String _pass = ""; // worker status protected boolean _working = false; public Worker(String host, String user, String pass) { this._host = host; this._user = user; this._pass = pass; } // Check if the worker is in use public boolean inUse() { return this._working; } @Override public void run() { this._ftp = new FTPClient(); this._connect(); } // Download a file from the ftp server public boolean download(String base, String path, String file) { this._working = true; boolean outcome = true; //create directory if not exists File pathDir = new File(base + path); if (!pathDir.exists()) { pathDir.mkdirs(); } //download file try { OutputStream output = new FileOutputStream(base + path + file); this._ftp.retrieveFile(file, output); output.close(); } catch (Exception e) { outcome = false; } finally { this._working = false; return outcome; } } // Connect to the server protected boolean _connect() { try { this._ftp.connect(this._host); this._ftp.login(this._user, this._pass); } catch (Exception e) { return false; } return this._ftp.isConnected(); } // Disconnect from the server protected void _disconnect() { try { this._ftp.disconnect(); } catch (Exception e) { /* do nothing */ } } } and basically i want to be able to call Worker.download(...) for each task in a queue whenever a worker becomes available without having to create a new connection to the ftp server for each download Any help would be appreciated as iv'e never used threads before and I'm going round in circles at the moment

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  • MonoTouch Load image in background

    - by user1058951
    I am having a problem trying to load an image and display it using System.Threading.Task My Code is as follows Task DownloadTask { get; set; } public string Instrument { get; set; } public PriceChartViewController(string Instrument) { this.Instrument = Instrument; DownloadTask = Task.Factory.StartNew(() => { }); } private void LoadChart(ChartType chartType) { NSData data = new NSData(); DownloadTask = DownloadTask.ContinueWith(prevTask => { try { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); data = NSData.FromUrl(nsUrl); } finally { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } }); DownloadTask = DownloadTask.ContinueWith(t => { UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; }, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.FromCurrentSynchronizationContext()); } The second Continue with does not seem to be being called? Initially my code looked like the following without the background processing and it worked perfectly. private void oldLoadChart(ChartType chartType) { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); NSData data = NSData.FromUrl(nsUrl); UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } Does anyone know what I am doing wrong?

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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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  • 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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  • Faking a Single Address Space

    - by dsimcha
    I have a large scientific computing task that parallelizes very well with SMP, but at too fine grained a level to be easily parallelized via explicit message passing. I'd like to parallelize it across address spaces and physical machines. Is it feasible to create a scheduler that would parallelize already multithreaded code across multiple physical computers under the following conditions: The code is already multithreaded and can scale pretty well on SMP configurations. The fact that not all of the threads are running in the same address space or on the same physical machine must be transparent to the program, even if this comes at a significant performance penalty in some use cases. You may assume that all of the physical machines involved are running operating systems and CPU architectures that are binary compatible. Things like locks and atomic operations may be slow (having network latency to deal with and all) but must "just work".

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  • "pseudo-atomic" operations in C++

    - by dan
    So I'm aware that nothing is atomic in C++. But I'm trying to figure out if there are any "pseudo-atomic" assumptions I can make. The reason is that I want to avoid using mutexes in some simple situations where I only need very weak guarantees. 1) Suppose I have globally defined volatile bool b, which initially I set true. Then I launch a thread which executes a loop while(b) doSomething(); Meanwhile, in another thread, I execute b=true. Can I assume that the first thread will continue to execute? In other words, if b starts out as true, and the first thread checks the value of b at the same time as the second thread assigns b=true, can I assume that the first thread will read the value of b as true? Or is it possible that at some intermediate point of the assignment b=true, the value of b might be read as false? 2) Now suppose that b is initially false. Then the first thread executes bool b1=b; bool b2=b; if(b1 && !b2) bad(); while the second thread executes b=true. Can I assume that bad() never gets called? 3) What about an int or other builtin types: suppose I have volatile int i, which is initially (say) 7, and then I assign i=7. Can I assume that, at any time during this operation, from any thread, the value of i will be equal to 7? 4) I have volatile int i=7, and then I execute i++ from some thread, and all other threads only read the value of i. Can I assume that i never has any value, in any thread, except for either 7 or 8? 5) I have volatile int i, from one thread I execute i=7, and from another I execute i=8. Afterwards, is i guaranteed to be either 7 or 8 (or whatever two values I have chosen to assign)?

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  • boost scoped_lock mutex crashes

    - by JahSumbar
    hello, I have protected a std::queue's access functions, push, pop, size, with boost::mutexes and boost::mutex::scoped_lock in these functions from time to time it crashes in a scoped lock the call stack is this: 0 0x0040f005 boost::detail::win32::interlocked_bit_test_and_set include/boost/thread/win32/thread_primitives.hpp 361 1 0x0040e879 boost::detail::basic_timed_mutex::timed_lock include/boost/thread/win32/basic_timed_mutex.hpp 68 2 0x0040e9d3 boost::detail::basic_timed_mutex::lock include/boost/thread/win32/basic_timed_mutex.hpp 64 3 0x0040b96b boost::unique_lock<boost::mutex>::lock include/boost/thread/locks.hpp 349 4 0x0040b998 unique_lock include/boost/thread/locks.hpp 227 5 0x00403837 MyClass::inboxSize - this is my inboxSize function that uses this code: MyClass::inboxSize () { boost::mutex::scoped_lock scoped_lock(m_inboxMutex); return m_inbox.size(); } and the mutex is declared like this: boost::mutex m_inboxMutex; it crashes at the last pasted line in this function: inline bool interlocked_bit_test_and_set(long* x,long bit) { long const value=1<<bit; long old=*x; and x has this value: 0xababac17 Thanks for the help

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