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  • Can threads safely read variables set by VCL events?

    - by Tom1952
    Is it safe for a thread to READ a variable set by a Delphi VCL event? When a user clicks on a VCL TCheckbox, the main thread sets a boolean to the checkbox's Checked state. CheckboxState := CheckBox1.Checked; At any time, a thread reads that variable if CheckBoxState then ... It doesn't matter if the thread "misses" a change to the boolean, because the thread checks the variable in a loop as it does other things. So it will see the state change eventually... Is this safe? Or do I need special code? Is surrounding the read and write of the variable (in the thread and main thread respectively) with critical code calls necessary and sufficient? As I said, it doesn't matter if the thread gets the "wrong" value, but I keep thinking that there might be a low-level problem if one thread tries to read a variable while the main thread is in the middle of writing it, or vice versa. My question is similar to this one: http://stackoverflow.com/questions/1353096/cross-thread-reading-of-a-variable. (Also related to my previous question: http://stackoverflow.com/questions/2449183/using-entercriticalsection-in-thread-to-update-vcl-label)

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  • Long running operations (threads) in a web (asp.net) environment

    - by rrejc
    I have an asp.net (mvc) web site. As the part of the functions I will have to support some long running operations, for example: Initiated from user: User can upload (xml) file to the server. On the server I need to extract file, do some manipulation (insert into the db) etc... This can take from one minute to ten minutes (or even more - depends on file size). Of course I don't want to block the request when the import is running , but I want to redirect user to some progress page where he will have a chance to watch the status, errors or even cancel the import. This operation will not be frequently used, but it may happen that two users at the same time will try to import the data. It would be nice to run the imports in parallel. At the beginning I was thinking to create a new thread in the iis (controller action) and run the import in a new thread. But I am not sure if this is a good idea (to create working threads on a web server). Should I use windows services or any other approach? Initiated from system: - I will have to periodically update lucene index with the new data. - I will have to send mass emails (in the future). Should I implement this as a job in the site and run the job via Quartz.net or should I also create a windows service or something? What are the best practices when it comes to running site "jobs"? Thanks!

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  • Python C API from C++ app - know when to lock

    - by Alex
    Hi Everyone, I am trying to write a C++ class that calls Python methods of a class that does some I/O operations (file, stdout) at once. The problem I have ran into is that my class is called from different threads: sometimes main thread, sometimes different others. Obviously I tried to apply the approach for Python calls in multi-threaded native applications. Basically everything starts from PyEval_AcquireLock and PyEval_ReleaseLock or just global locks. According to the documentation here when a thread is already locked a deadlock ensues. When my class is called from the main thread or other one that blocks Python execution I have a deadlock. Python Cfunc1() - C++ func that creates threads internally which lead to calls in "my class", It stuck on PyEval_AcquireLock, obviously the Python is already locked, i.e. waiting for C++ Cfunc1 call to complete... It completes fine if I omit those locks. Also it completes fine when Python interpreter is ready for the next user command, i.e. when thread is calling funcs in the background - not inside of a native call I am looking for a workaround. I need to distinguish whether or not the global lock is allowed, i.e. Python is not locked and ready to receive the next command... I tried PyGIL_Ensure, unfortunately I see hang. Any known API or solution for this ? (Python 2.4)

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  • Create a Task list, with tasks without executing

    - by Ernesto Araya Eguren
    I have an async method private async Task DoSomething(CancellationToken token) a list of Tasks private List<Task> workers = new List<Task>(); and I have to create N threads that runs that method public void CreateThreads(int n) { tokenSource = new CancellationTokenSource(); token = tokenSource.Token; for (int i = 0; i < n; i++) { workers.Add(DoSomething(token)); } } but the problem is that those have to run at a given time public async Task StartAllWorkers() { if (0 < workers.Count) { try { while (0 < workers.Count) { Task finishedWorker = await Task.WhenAny(workers.ToArray()); workers.Remove(finishedWorker); finishedWorker.Dispose(); } if (workers.Count == 0) { tokenSource = null; } } catch (OperationCanceledException) { throw; } } } but actually they run when i call the CreateThreads Method (before the StartAllWorkers). I searched for keywords and problems like mine but couldn't find anything about stopping the task from running. I've tried a lot of different aproaches but anything that could solve my problem entirely. For example, moving the code from DoSomething into a workers.Add(new Task(async () => { }, token)); would run the StartAllWorkers(), but the threads will never actually start. There is another method for calling the tokenSource.Cancel().

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  • lock shared data using c#

    - by menacheb
    Hi, I have a program (C#) with a list of tests to do. Also, I have two thread. one to add task into the list, and one to read and remove from it the performed tasks. I'm using the 'lock' function each time one of the threads want to access to the list. Another thing I want to do is, if the list is empty, the thread who need to read from the list will sleep. and wake up when the first thread add a task to the list. Here is the code I wrote: ... List<String> myList = new List(); Thread writeThread, readThread; writeThread = new Thread(write); writeThread.Start(); readThraed = new Thread(read); readThread.Start(); ... private void write() { while(...) { ... lock(myList) { myList.Add(...); } ... if (!readThread.IsAlive) { readThraed = new Thread(read); readThread.Start(); } ... } ... } private void read() { bool noMoreTasks = false; while (!noMoreTasks) { lock (MyList)//syncronize with the ADD func. { if (dataFromClientList.Count > 0) { String task = myList.First(); myList.Remove(task); } else { noMoreTasks = true; } } ... } readThread.Abort(); } Apparently I did it wrong, and it's not performed as expected (The readTread does't read from the list). Does anyone know what is my problem, and how to make it right? Many thanks,

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  • How to implement blocking request-reply using Java concurrency primitives?

    - by Uri
    My system consists of a "proxy" class that receives "request" packets, marshals them and sends them over the network to a server, which unmarshals them, processes, and returns some "response packet". My "submit" method on the proxy side should block until a reply is received to the request (packets have ids for identification and referencing purposes) or until a timeout is reached. If I was building this in early versions of Java, I would likely implement in my proxy a collection of "pending messages ids", where I would submit a message, and wait() on the corresponding id (with a timeout). When a reply was received, the handling thread would notify() on the corresponding id. Is there a better way to achieve this using an existing library class, perhaps in java.util.concurrency? If I went with the solution described above, what is the correct way to deal with the potential race condition where a reply arrives before wait() is invoked?

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  • Cocoa multiple threads, 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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  • STA threads with SQLXMLBULKLOAD

    - by Christopher
    If I have N STA .NET Threads each performing an independent bulk load operation on a different database using the SQLXMLBulkLoad dll (which requires calling threads to be STA), is it possible for all bulk loads to be happening at the same time, or are they implicitly serialized due to the STA COM configuration? Thanks!

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  • Rails running multiple delayed_job - lock tables

    - by pepernik
    Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

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  • Message queue proxy in Python + Twisted

    - by gasper_k
    Hi, I want to implement a lightweight Message Queue proxy. It's job is to receive messages from a web application (PHP) and send them to the Message Queue server asynchronously. The reason for this proxy is that the MQ isn't always avaliable and is sometimes lagging, or even down, but I want to make sure the messages are delivered, and the web application returns immediately. So, PHP would send the message to the MQ proxy running on the same host. That proxy would save the messages to SQLite for persistence, in case of crashes. At the same time it would send the messages from SQLite to the MQ in batches when the connection is available, and delete them from SQLite. Now, the way I understand, there are these components in this service: message listener (listens to the messages from PHP and writes them to a Incoming Queue) DB flusher (reads messages from the Incoming Queue and saves them to a database; due to SQLite single-threadedness) MQ connection handler (keeps the connection to the MQ server online by reconnecting) message sender (collects messages from SQlite db and sends them to the MQ server, then removes them from db) I was thinking of using Twisted for #1 (TCPServer), but I'm having problem with integrating it with other points, which aren't event-driven. Intuition tells me that each of these points should be running in a separate thread, because all are IO-bound and independent of each other, but I could easily put them in a single thread. Even though, I couldn't find any good and clear (to me) examples on how to implement this worker thread aside of Twisted's main loop. The example I've started with is the chatserver.py, which uses service.Application and internet.TCPServer objects. If I start my own thread prior to creating TCPServer service, it runs a few times, but the it stops and never runs again. I'm not sure, why this is happening, but it's probably because I don't use threads with Twisted correctly. Any suggestions on how to implement a separate worker thread and keep Twisted? Do you have any alternative architectures in mind?

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  • Java Random Slowdowns on Mac OS cont'd

    - by javajustice
    I asked this question a few weeks ago, but I'm still having the problem and I have some new hints. The original question is here: http://stackoverflow.com/questions/1651887/java-random-slowdowns-on-mac-os Basically, I have a java application that splits a job into independent pieces and runs them in separate threads. The threads have no synchronization or shared memory items. The only resources they do share are data files on the hard disk, with each thread having an open file channel. Most of the time it runs very fast, but occasionally it will run very slow for no apparent reason. If I attach a CPU profiler to it, then it will start running quickly again. If I take a CPU snapshot, it says its spending most of its time in "self time" in a function that doesn't do anything except check a few (unshared unsynchronized) booleans. I don't know how this could be accurate because 1, it makes no sense, and 2, attaching the profiler seems to knock the threads out of whatever mode they're in and fix the problem. Also, regardless of whether it runs fast or slow, it always finishes and gives the same output, and it never dips in total cpu usage (in this case ~1500%), implying that the threads aren't getting blocked. I have tried different garbage collectors, different sizings the parts of the memory space, writing data output to non-raid drives, and putting all data output in threads separate the main worker threads. Does anyone have any idea what kind of problem this could be? Could it be the operating system (OS X 10.6.2) ? I have not been able to duplicate it on a windows machine, but I don't have one with a similar hardware configuration.

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  • Will creating a background thread in a WCF service during a call, take up a thread in the ASP .NET t

    - by Nate Pinchot
    The following code is part of a WCF service. Will eventWatcher take up a thread in the ASP .NET thread pool, even if it is set IsBackground = true? /// <summary> /// Provides methods to work with the PhoneSystem web services SDK. /// This is a singleton since we need to keep track of what lines (extensions) are open. /// </summary> public sealed class PhoneSystemWebServiceFactory : IDisposable { // singleton instance reference private static readonly PhoneSystemWebServiceFactory instance = new PhoneSystemWebServiceFactory(); private static readonly object l = new object(); private static volatile Hashtable monitoredExtensions = new Hashtable(); private static readonly PhoneSystemWebServiceClient webServiceClient = CreateWebServiceClient(); private static volatile bool isClientRegistered; private static volatile string clientHandle; private static readonly Thread eventWatcherThread = new Thread(EventPoller) {IsBackground = true}; #region Constructor // these constructors are hacks to make the C# compiler not mark beforefieldinit // more info: http://www.yoda.arachsys.com/csharp/singleton.html static PhoneSystemWebServiceFactory() { } PhoneSystemWebServiceFactory() { } #endregion #region Properties /// <summary> /// Gets a thread safe instance of PhoneSystemWebServiceFactory /// </summary> public static PhoneSystemWebServiceFactory Instance { get { return instance; } } #endregion #region Private methods /// <summary> /// Create and configure a PhoneSystemWebServiceClient with basic http binding and endpoint from app settings. /// </summary> /// <returns>PhoneSystemWebServiceClient</returns> private static PhoneSystemWebServiceClient CreateWebServiceClient() { string url = ConfigurationManager.AppSettings["PhoneSystemWebService_Url"]; if (string.IsNullOrEmpty(url)) { throw new ConfigurationErrorsException( "The AppSetting \"PhoneSystemWebService_Url\" could not be found. Check the application configuration and ensure that the element exists. Example: <appSettings><add key=\"PhoneSystemWebService_Url\" value=\"http://xyz\" /></appSettings>"); } return new PhoneSystemWebServiceClient(new BasicHttpBinding(), new EndpointAddress(url)); } #endregion #region Event poller public static void EventPoller() { while (true) { if (Thread.CurrentThread.ThreadState == ThreadState.Aborted || Thread.CurrentThread.ThreadState == ThreadState.AbortRequested || Thread.CurrentThread.ThreadState == ThreadState.Stopped || Thread.CurrentThread.ThreadState == ThreadState.StopRequested) break; // get events //webServiceClient.GetEvents(clientHandle, 30, 100); } Thread.Sleep(5000); } #endregion #region Client registration methods private static void RegisterClientIfNeeded() { if (isClientRegistered) { return; } lock (l) { // double lock check if (isClientRegistered) { return; } //clientHandle = webServiceClient.RegisterClient("PhoneSystemWebServiceFactoryInternal", null); isClientRegistered = true; } } private static void UnregisterClient() { if (!isClientRegistered) { return; } lock (l) { // double lock check if (!isClientRegistered) { return; } //webServiceClient.UnegisterClient(clientHandle); } } #endregion #region Phone extension methods public bool SubscribeToEventsForExtension(string extension) { if (monitoredExtensions.Contains(extension)) { return false; } lock (monitoredExtensions.SyncRoot) { // double lock check if (monitoredExtensions.Contains(extension)) { return false; } RegisterClientIfNeeded(); // open line so we receive events for extension LineInfo lineInfo; try { //lineInfo = webServiceClient.OpenLine(clientHandle, extension); } catch (FaultException<PhoneSystemWebSDKErrorDetail>) { // TODO: log error return false; } // add extension to list of monitored extensions //monitoredExtensions.Add(extension, lineInfo.lineID); monitoredExtensions.Add(extension, 1); // start event poller thread if not already started if (eventWatcherThread.ThreadState == ThreadState.Stopped || eventWatcherThread.ThreadState == ThreadState.Unstarted) { eventWatcherThread.Start(); } return true; } } public bool UnsubscribeFromEventsForExtension(string extension) { if (!monitoredExtensions.Contains(extension)) { return false; } lock (monitoredExtensions.SyncRoot) { if (!monitoredExtensions.Contains(extension)) { return false; } // close line try { //webServiceClient.CloseLine(clientHandle, (int) monitoredExtensions[extension]); } catch (FaultException<PhoneSystemWebSDKErrorDetail>) { // TODO: log error return false; } // remove extension from list of monitored extensions monitoredExtensions.Remove(extension); // if we are not monitoring anything else, stop the poller and unregister the client if (monitoredExtensions.Count == 0) { eventWatcherThread.Abort(); UnregisterClient(); } return true; } } public bool IsExtensionMonitored(string extension) { lock (monitoredExtensions.SyncRoot) { return monitoredExtensions.Contains(extension); } } #endregion #region Dispose public void Dispose() { lock (l) { // close any open lines var extensions = monitoredExtensions.Keys.Cast<string>().ToList(); while (extensions.Count > 0) { UnsubscribeFromEventsForExtension(extensions[0]); extensions.RemoveAt(0); } if (!isClientRegistered) { return; } // unregister web service client UnregisterClient(); } } #endregion }

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  • Why AutoResetEvent and ManualResetEvent does not support name in the constructor?

    - by Ikaso
    On .NET Framework 2.0 AutoResetEvent and ManualResetEvent inherit from EventWaitHandle. The EventWaitHandle class has 4 different constructors. 3 of the constructors support giving a name to the event. On the other hand both ManualResetEvent and AutoResetEvent do not support naming and provide a single constructor that receives the initialState. I can simply inherit from EventWaitHandle and write my own implementation of those classes that support all the constructor overloads, but I don't like to re-invent the wheel if I do not have to. My questions are: Is there a special problem in naming events? Do you have any idea why Microsoft did not support it? Do you have a proposal better than inheriting from the EventWaitHandle class and calling the appropriate constructor as in the following example? public class MyAutoResetEvent: EventWaitHandle { public MyAutoResetEvent(bool initialState) : base(initialState, EventResetMode.AutoReset) { } public MyAutoResetEvent(bool initialState, string name) : base(initialState, EventResetMode.AutoReset, name) { } public MyAutoResetEvent(bool initialState, string name, out bool createdNew) : base(initialState, EventResetMode.AutoReset, name, out createdNew) { } public MyAutoResetEvent(bool initialState, string name, out bool createdNew, EventWaitHandleSecurity eventSecurity) : base(initialState, EventResetMode.AutoReset, string.Empty, out createdNew, eventSecurity) { } }

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  • Python: Script works, but seems to deadlock after some time

    - by sberry2A
    I have the following script, which is working for the most part Link to PasteBin The script's job is to start a number of threads which in turn each start a subprocess with Popen. The output from each subprocess is as follows: 1 2 3 . . . n Done Bascially the subprocess is transferring 10M records from tables in one database to different tables in another db with a lot of data massaging/manipulation in between because of the different schemas. If the subprocess fails at any time in it's execution (bad records, duplicate primary keys, etc), or it completes successfully, it will output "Done\n". If there are no more records to select against for transfer then it will output "NO DATA\n" My intent was to create my script "tableTransfer.py" which would spawn a number of these processes, read their output, and in turn output information such as number of updates completed, time remaining, time elapsed, and number of transfers per second. I started running the process last night and checked in this morning to see it had deadlocked. There were not subprocceses running, there are still records to be updated, and the script had not exited. It was simply sitting there, no longer outputting the current information because no subprocces were running to update the total number complete which is what controls updates to the output. This is running on OS X. I am looking for three things: I would like to get rid of the possibility of this deadlock occurring so I don't need to check in on it as frequently. Is there some issue with locking? Am I doing this in a bad way (gThreading variable to control looping of spawning additional thread... etc.) I would appreciate some suggestions for improving my overall methodology. How should I handle ctrl-c exit? Right now I need to kill the process, but assume I should be able to use the signal module or other to catch the signal and kill the threads, is that right? I am not sure whether I should be pasting my entire script here, since I usually just paste snippets. Let me know if I should paste it here as well.

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  • How the simples GUI countdown is supposed to work?

    - by Roman
    I am trying to write the simples GUI countdown. I found in Internet some code but it is already too fancy for me. I am trying to keep it as simple as possible. So, I just want to have a window saying "You have 10 second left". The number of second should decrease every second from 10 to 0. I wrote a code. And I think I am close to the working solution. But I still missing something. Could you pleas help me to find out what is wrong? Here is my code: import javax.swing.*; public class Countdown { static JLabel label; // Method which defines the appearance of the window. private static void showGUI() { JFrame frame = new JFrame("Simple Countdown"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JLabel label = new JLabel("Some Text"); frame.add(label); frame.pack(); frame.setVisible(true); } // Define a new thread in which the countdown is counting down. static Thread counter = new Thread() { public void run() { for (int i=10; i>0; i=i-1) { updateGUI(i,label); try {Thread.sleep(1000);} catch(InterruptedException e) {}; } } }; // A method which updates GUI (sets a new value of JLabel). private static void updateGUI(final int i, final JLabel label) { SwingUtilities.invokeLater(new Runnable(i,label) { public Runnable(int i, JLabel label) { this.i = i; this.label = label; } public void run() { label.setText("You have " + i + " seconds."); } }); } // The main method (entry point). public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { showGUI(); //counter.start(); } }); //counter.start(); } } And I have several concrete question about this code: Where should I place the counter.start();? (In my code I put it on 2 places. Which one is correct?) Why compiler complains about the constructor for Runnable? It says that I have an invalid method declaration and I need to specify the returned type. ADDED: I made the suggested corrections. And then I execute the code and get: Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at Worker.run(Worker.java:12) In the Worker.java in the line 12 I have: label.setText("You have " + i + " seconds.");.

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  • CollectionChanged notification across threads?

    - by Mark
    I'm writing a download manager using C#/WPF, and I just encountered this error: This type of CollectionView does not support changes to its SourceCollection from a thread different from the Dispatcher thread. The basic flow of my program is that a few web pages/downloads are enqueued at the start, and then they're downloaded asynchronously. When an HTML page has completed downloading, I parse it and look for more stuff to download, then enqueue it directly from within the worker thread. I get that error when trying to send out the CollectionChanged event on my customized queue class. However, I need to fire that event so that the GUI can get updated. What are my options?

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  • In app purchase on iphone.: How to receive your available products *before* someone may be able to b

    - by Thorsten S.
    Currently I am loading my supported products from a plist and after that I send a SKProductsRequest to guarantee that my SKProducts are still valid. So I set up the request, start it and get the response in: (void)productsRequest:(SKProductsRequest *)request didReceiveResponse:(SKProductsResponse *)response Now, so far all functions correctly. Problem: From calling the request until receiving the response it may last several seconds. Until that my app is already loaded and the user may be able to choose and buy a product. But because no products have been received, the available products are not in sync with the validated products - unlikely, but possible error. So my idea is to wait until the data is loaded and only continue when the list is validated. (Just a few seconds waiting...). I have a singleton instance managing all products. + (MyClass *) sharedInstance { if (!sharedInstance) sharedInstance = [MyClass new]; // Now wait until we have our data [condition lock]; while (noEntriesYet) // is yes at begin [condition wait]; [condition unlock]; return sharedInstance; } - productsRequest: didReceiveResponse: { [condition lock]; // I have my data noEntriesYet = false; [condition signal]; [condition unlock]; } Problem: The app freezes. Everything works fine if didReceiveResponse is completed before the sharedInstance is queried. There are different threads, the lock is working if wait is reached during didReceiveResponse, everything fine. But if not, didReceiveResponse is never called even if the request was sent. The lock is released, everything looks ok. I have tried to send the product request in a separate NSThread, with NSOperationQueue...without avail. Why ? What is happening ? How to solve the problem ?

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  • cache-coherence MOESI protocol

    - by Yaron
    processor A owns a cache line which is shared with processor B. what happens when B tries to write to that line? also, if it was 'invalid' instead of 'shared' would it make any difference? thank you.

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  • Will Multi threading increase the speed of the calculation on Single Processor

    - by Harsha
    On a single processor, Will multi-threading increse the speed of the calculation. As we all know that, multi-threading is used for Increasing the User responsiveness and achieved by sepating UI thread and calculation thread. But lets talk about only console application. Will multi-threading increases the speed of the calculation. Do we get culculation result faster when we calculate through multi-threading. what about on multi cores, will multi threading increse the speed or not. Please help me. If you have any material to learn more about threading. please post. Thanks in advance, Harsha

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  • Is there an use case for non-blocking receive when I have threads?

    - by Gabriel Šcerbák
    I know non-blocking receive is not used as much in message passing, but still some intuition tells me, it is needed. Take for example GUI event driven applications, you need some way to wait for a message in a non-blocking way, so your program can execute some computations. One of the ways to solve this is to have a special thread with message queue. Is there some use case, where you would really need non-blocking receive even if you have threads?

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  • Non-blocking MySQL updates with java?

    - by justkevin
    For a multiplayer game I'm working on I'd like to record events to the mysql database without blocking the game update thread so that if the database is busy or a table is locked the game doesn't stop running while it waits for a write. What's the best way to accomplish this? I'm using c3p0 to manage the database connection pool. My best idea so far is to add query update strings to a synchronized list with an independent thread checking the list every 100ms and executing the queries it finds there.

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  • Using SetParent to steal the main window of another process but keeping the message loops separate

    - by insta
    Background: My coworker and I are maintaining a million-line legacy application we inherited. Its frontend is written in VB6, and as we're devoting almost all of our resources to converting it to C#, we are looking for quick & dirty solutions to our specific problem. The application behaves in a plugin-ish manner. There are up to 20ish separate ActiveX controls that can be loaded at once in a grid-style layout. The problem is that the ActiveX controls do all of their processing on their own UI thread, and as a lot of it is blocking waiting on network access, the UI gets very soupy. When our hosting C# app loads these controls, it becomes unresponsive because of how many controls are chewing up UI resources doing nothing. To top it off, the controls are fragile and will crash at the slightest provocation. When they are hosted in the main C# app, it creates serious instability. The best my coworker and I have come up with so far is starting a process per ActiveX control. This process, which we call the proxy, is another winforms app. It uses named pipes to communicate with the hosting process. The hosting process creates a window, loads an ActiveX control of our choice (via some reflections & AxHost magic), and tells the main process what its window handle is via the named pipe. The main process uses a combination of SetParent, and SetWindowPos to move the proxy application into itself to emulate a plugin. Size updates are sent via the named pipe. This works well enough until the ActiveX application does some sort of lengthy process and we click around on the main window while it's working. For awhile the main window is responsive, but eventually it becomes unresponsive as the child window waits for its UI thread. How can we keep the child windows on their own complete thread while still getting the benefits of SetParent? (please let me know if anything isn't clear!)

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