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• Multithreading: Read from / write to a pipe

  - by Tero Jokinen

  I write some data to a pipe - possibly lots of data and at random intervals. How to read the data from the pipe? Is this ok: in the main thread (current process) create two more threads (2, 3) the second thread writes sometimes to the pipe (and flush-es the pipe?) the 3rd thread has infinite loop which reads the pipe (and then sleeps for some time) Is this so far correct? Now, there are a few thing I don't understand: do I have to lock (mutex?) the pipe on write? IIRC, when writing to pipe and its buffer gets full, the write end will block until I read the already written data, right? How to check for read data in the pipe, not too often, not too rarely? So that the second thread wont block? Is there something like select for pipes? It is possible to set the pipe to unbuffered more or I have to flush it regularly - which one is better? Should I create one more thread, just for flushing the pipe after write? Because flush blocks as well, when the buffer is full, right? I just don't want the 1st and 2nd thread to block.... [Edit] Sorry, I thought the question is platform agnostic but just in case: I'm looking at this from Win32 perspective, possibly MinGW C...

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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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• 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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• Core Data Errors vs Exceptions Part 3

  - by John Gallagher

  My question is similar to this one. Background I'm creating a large number of objects in a core data store using NSOperations to speed things up. I've followed all the Core Data multithreading rules - I've got a single persistent store coordinator and a managed object context per thread that on save is merging back to the main managed object context. The Problem When the number of threads running at once is more than 1, I get the exception logged on save of my core data store: NSExceptionHandler has recorded the following exception: NSInternalInconsistencyException -- optimistic locking failure What I've Tried My code that creates new entities is quite complex - it makes entities that have relationships with other entities that could be being created in a separate thread. If I replace my object creation routine with some very simple code just making non-related entries, everything works perfectly. Initially, as well as the exceptions, I was getting a save error saying core data couldn't save due to the merge failing. I read the docs and realised I needed a merge policy on the Managed Object Context I was saving to. I set this up and as this question states, the save error goes away, but the exception remains. My Question Do I need to worry about these exceptions? If I do need to get rid of the exceptions, any ideas on how I do it?

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• Handling exceptions in Prism 4 modules

  - by marcellscarlett

  I've gone through a number of threads here about this topic with no success. It seems that in the App.xaml.cs of our WPF application, handling DispatcherUnhandledExceptions and AppDomain.CurrentDomain.UnhandledException don't catch everything. In this specific instance we have 7 prism modules. My exception handling code is below (almost identical for UnhandledException): private void OnDispatcherUnhandledException(object sender, DispatcherUnhandledExceptionEventArgs e) { try { var ex = e.Exception.InnerException ?? e.Exception; var logManager = new LogManager(); logManager.Error(ex); if (!EventLog.SourceExists(ex.Source)) EventLog.CreateEventSource(ex.Source, "AppName"); EventLog.WriteEntry(ex.Source, ex.InnerException.ToString()); var emb = new ExceptionMessageBox(ex); emb.ShowDialog(); e.Handled = true; } catch (Exception) { } } The problem seems to be the unhandled exceptions occurring in the modules. They aren't caught by the code above and they cause the application to crash without logging or displaying any sort of message. Does anyone have experience with this?

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• Implementing deadlock condition

  - by Bhaskar

  I am trying to implementing deadlock condition but somehow I am not able to get it working. Both the threads Thread1 and Thread2 are entering in the run function but only one of them enters in Sub/Sum depending on who entered run first. Example : if Thread2 entered run first the it will call sub() and Thread1 never calls sum(). I have also added sleep time so that Thread2 sleeps before calling sum() and Thread1 gets enough time to enter Sum() but Thread1 never enters. public class ExploringThreads { public static void main(String[] args) { // TODO Auto-generated method stub threadexample a1 = new threadexample(); Thread t1 = new Thread(a1, "Thread1"); Thread t2 = new Thread(a1,"Thread2"); t1.start(); t2.start(); } } class threadexample implements Runnable{ public int a = 10; public void run(){ if(Thread.currentThread().getName().equals("Thread1")) sum(); else if(Thread.currentThread().getName().equals("Thread2")) sub(); } public synchronized void sum() { try { Thread.sleep(2000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"In Sum"); sub(); } public synchronized void sub() { try { Thread.sleep(2000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } System.out.println(Thread.currentThread().getName()+"In Sub"); sum(); } }

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• How to properly cast a global memory array using the uint4 vector in CUDA to increase memory throughput?

  - by charis

  There are generally two techniques to increase the memory throughput of the global memory on a CUDA kernel; memory accesses coalescence and accessing words of at least 4 bytes. With the first technique accesses to the same memory segment by threads of the same half-warp are coalesced to fewer transactions while be accessing words of at least 4 bytes this memory segment is effectively increased from 32 bytes to 128. To access 16-byte instead of 1-byte words when there are unsigned chars stored in the global memory, the uint4 vector is commonly used by casting the memory array to uint4: uint4 *text4 = ( uint4 * ) d_text; var = text4[i]; In order to extract the 16 chars from var, i am currently using bitwise operations. For example: s_array[j * 16 + 0] = var.x & 0x000000FF; s_array[j * 16 + 1] = (var.x >> 8) & 0x000000FF; s_array[j * 16 + 2] = (var.x >> 16) & 0x000000FF; s_array[j * 16 + 3] = (var.x >> 24) & 0x000000FF; My question is, is it possible to recast var (or for that matter *text4) to unsigned char in order to avoid the additional overhead of the bitwise operations?

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• Thread-Safe lazy instantiating using MEF

  - by Xaqron

  // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Lazy load images in UITableViewCell

  - by lostInTransit

  Hi I have some 50 custom cells in my UITableView. I want to display an image and a label in the cells where I get the images from URLs. I want to do a lazy load of images so the UI does not freeze up while the images are being loaded. I tried getting the images in separate threads but I have to load each image every time a cell becomes visible again (Otherwise reuse of cells shows old images) Apps like Facebook load images only for cells currently visible and once the images are loaded, they are not loaded again. Can someone please tell me how to duplicate this behavior. Thanks. Edit Trying to cache images in an NSMutableDictionary object creates problems when the user scrolls fast. I am getting images only when scrolling completely stops and clearing out the cache on memory warning. But the app invariably gets a memory warning (due to size of images being cached) and clears the cache before reloading. If scrolling is very fast, it crashes. Any other suggestions are welcome

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• Peculiar JRE behaviour running RMI server under load, should I worry?

  - by darri

  I've been developing a minimalistic Java rich client CRUD application framework for the past few years, mostly as a hobby but also actively using it to write applications for my current employer. The framework provides database access to clients either via a local JDBC based connection or a lightweight RMI server. Last night I started a load testing application, which ran 100 headless clients, bombarding the server with requests, each client waiting only 1 - 2 seconds between running simple use cases, consisting of selecting records along with associated detail records from a simple e-store database (Chinook). This morning when I looked at the telemetry results from the server profiling session I noticed something which to me seemed strange (and made me keep the setup running for the remainder of the day), I don't really know what conclusions to draw from it. Here are the results: Memory GC activity Threads CPU load Interesting, right? So the question is, is this normal or erratic? Is this simply the JRE (1.6.0_03 on Windows XP) doing it's thing (perhaps related to the JRE configuration) or is my framework design somehow causing this? Running the server against MySQL as opposed to an embedded H2 database does not affect the pattern. I am leaving out the details of my server design, but I'll be happy to elaborate if this behaviour is deemed erratic.

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• Making Extension method Generic

  - by Ian

  In this post there's a very interesting way of updating UI threads using a static extension method. public static void InvokeIfRequired(this Control c, Action<Control> action) { if(c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } What I want to do, is to make a generic version, so I'm not constrained by a control. This would allow me to do the following for example (because I'm no longer constrained to just being a Control) this.progressBar1.InvokeIfRequired(pb => pb.Value = e.Progress); I've tried the following: public static void InvokeIfRequired<T>(this T c, Action<T> action) where T : Control { if (c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } But I get the following error that I'm not sure how to fix. Anyone any suggestions? Error 5 Cannot convert lambda expression to type 'System.Delegate' because it is not a delegate type

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• Java - A better to run code for a period of time

  - by mhollander38

  I need to run some code for a predefined length of time, when the time is up it needs to stop. Currently I am using a TimerTask to allow the code to execute for a set amount of time but this is causing endless threads to be created by the code and is just simply not efficient. Is there a better alternative? Current code; // Calculate the new lines to draw Timer timer3 = new Timer(); timer3.schedule(new TimerTask(){ public void run(){ ArrayList<String> Coords = new ArrayList<String>(); int x = Float.valueOf(lastFour[0]).intValue(); int y = Float.valueOf(lastFour[1]).intValue(); int x1 = Float.valueOf(lastFour[2]).intValue(); int y1 = Float.valueOf(lastFour[3]).intValue(); //Could be the wrong way round (x1,y1,x,y)? Coords = CoordFiller.coordFillCalc(x, y, x1, y1); String newCoOrds = ""; for (int j = 0; j < Coords.size(); j++) { newCoOrds += Coords.get(j) + " "; } newCoOrds.trim(); ClientStorage.storeAmmendedMotion(newCoOrds); } } ,time);

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• Another thread safe queue implementation

  - by jensph

  I have a class, Queue, that I tried to make thread safe. It has these three member variables: std::queue<T> m_queue; pthread_mutex_t m_mutex; pthread_cond_t m_condition; and a push and pop implemented as: template<class T> void Queue<T>::push(T value) { pthread_mutex_lock( &m_mutex ); m_queue.push(value); if( !m_queue.empty() ) { pthread_cond_signal( &m_condition ); } pthread_mutex_unlock( &m_mutex ); } template<class T> bool Queue<T>::pop(T& value, bool block) { bool rtn = false; pthread_mutex_lock( &m_mutex ); if( block ) { while( m_queue.empty() ) { pthread_cond_wait( &m_condition, &m_mutex ); } } if( !m_queue.empty() ) { value = m_queue.front(); m_queue.pop(); rtn = true; } pthread_mutex_unlock( &m_mutex ); return rtn; } Unfortunately there are occasional issues that may be the fault of this code. That is, there are two threads and sometimes thread 1 never comes out of push() and at other times thread 2 never comes out of pop() (the block parameter is true) though the queue isn't empty. I understand there are other implementations available, but I'd like to try to fix this code, if needed. Anyone see any issues? The constructor has the appropriate initializations: Queue() { pthread_mutex_init( &mMutex, NULL ); pthread_cond_init( &mCondition, NULL ); } and the destructor, the corresponding 'destroy' calls.

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• New to J2EE; architecture suggestions for a service/daemon?

  - by Kate

  I am brand new to the J2EE world. As an exercise to try and familiarize myself with J2EE, I'm trying to create a tiered web-app, but I'm getting a little stuck on what the best way is to spin up a service in the background that does work. Paramters of the service: It must open and hold a socket connection and receive information from the connected server. There is a 1-to-1 correlation between a user and a new socket connection. So the idea is the user presses a button on the web-page, and somewhere on the server a socket connection is opened. For the remainder of the users session (or until the user presses some sort of disconnect button) the socket remains open and pushes received information to some sort of centralized store that servlets can query and return to the user via AJAX. Is there a J2EE type way to handle this situation? Naturally what I would think to do is to just write a Java application that listens on a port that the servlets can connect to and spawns new threads that open these sockets, but that seems very ad-hoc to me. (PS: I am also new to Stack Overflow, so forgive me if it takes me some time to figure the site out!)

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• .NET Best Way to move many files to and from various directories??

  - by Dan

  I've created a program that moves files to and from various directories. An issue I've come across is when you're trying to move a file and some other program is still using it. And you get an error. Leaving it there isn't an option, so I can only think of having to keep trying to move it over and over again. This though slows the entire program down, so I create a new thread and let it deal with the problem file and move on to the next. The bigger problem is when you have too many of these problem files and the program now has so many threads trying to move these files, that it just crashes with some kernel.dll error. Here's a sample of the code I use to move the files: Public Sub MoveIt() Try File.Move(_FileName, _CopyToFileName) Catch ex As Exception Threading.Thread.Sleep(5000) MoveIt() End Try End Sub As you can see.. I try to move the file, and if it errors, I wait and move it again.. over and over again.. I've tried using FileInfo as well, but that crashes WAY sooner than just using the File object. So has anyone found a fool proof way of moving files without it ever erroring? Note: it takes a lot of files to make it crash. It'll be fine on the weekend, but by the end of the day on monday, it's done.

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• Chat app vs REST app - use a thread in an Activity or a thread in a Service?

  - by synic

  In Virgil Dobjanschi's talk, "Developing Android REST client applications" (link here), he said a few things that took me by surprise. Including: Don't run http queries in threads spawned by your activities. Instead, communicate with a service to do them, and store the information in a ContentProvider. Use a ContentObserver to be notified of changes. Always perform long running tasks in a Service, never in your Activity. Stop your Service when you're done with it. I understand that he was talking about a REST API, but I'm trying to make it fit with some other ideas I've had for apps. One of APIs I've been using uses long-polling for their chat interface. There is a loop http queries, most of which will time out. This means that, as long as the app hasn't been killed by the OS, or the user hasn't specifically turned off the chat feature, I'll never be done with the Service, and it will stay open forever. This seems less than optimal. Long question short: For a chat application that uses long polling to simulate push and immediate response, is it still best practice to use a Service to perform the HTTP queries, and store the information in a ContentProvider?

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• JSON to display text -- Freezes UI

  - by Adam Storr

  Hi everyone, I currently have a very simple view which displays info from a JSON feed. The problem I'm facing is the few second pause I encounter once I press this tab. How can I make this view load instantly and then have the label.text areas load after? Preferable with an activity indicator? Should I use threads? Thanks in advance! Code: - (NSString *)stringWithUrl:(NSURL *)url { NSURLRequest *urlRequest = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReloadRevalidatingCacheData timeoutInterval:30]; NSData *urlData; NSURLResponse *response; NSError *error; urlData = [NSURLConnection sendSynchronousRequest:urlRequest returningResponse:&response error:&error]; return [[NSString alloc] initWithData:urlData encoding:NSUTF8StringEncoding]; } - (id)objectWithUrl:(NSURL *)url { SBJsonParser *jsonParser = [SBJsonParser new]; NSString *jsonString = [self stringWithUrl:url]; return [jsonParser objectWithString:jsonString error:NULL]; } - (NSDictionary *)downloadStats { id response = [self objectWithUrl:[NSURL URLWithString:@"http://www.example.com/JSON"]]; NSDictionary *feed = (NSDictionary *)response; return feed; [feed release]; } - (void)viewDidLoad { [super viewDidLoad]; [GlobalStatsScrollView setScrollEnabled:YES]; [GlobalStatsScrollView setContentSize:CGSizeMake(320, 360)]; } - (void)viewWillAppear:(BOOL)animated { NSLog(@"View appears"); // Download JSON Feed NSDictionary *feed = [self downloadStats]; totalproduced.text = [feed valueForKey:@"Produced"]; totalno.text = [feed valueForKey:@"Total"]; mostcommon.text = [feed valueForKey:@"Most Common"]; }

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• Why doesn't Win Forms application update label immediately?

  - by rosscj2533

  I am doing some experimenting with threads, and made a 'control' method to compare against where all the processing happens in the UI thread. It should run a method, which will update a label at the end. This method runs four times, but the labels are not updated until all 4 have completed. I expected one label to get updated about every 2 seconds. Here's the code: private void button1_Click(object sender, EventArgs e) { Stopwatch watch = new Stopwatch(); watch.Start(); UIThreadMethod(lblOne); UIThreadMethod(lblTwo); UIThreadMethod(lblThree); UIThreadMethod(lblFour); watch.Stop(); lblTotal.Text = "Total Time (ms): " + watch.ElapsedMilliseconds.ToString(); } private void UIThreadMethod(Label label) { Stopwatch watch = new Stopwatch(); watch.Start(); for (int i = 0; i < 10; i++) { Thread.Sleep(200); } watch.Stop(); // this doesn't set text right away label.Text = "Done, Time taken (ms): " + watch.ElapsedMilliseconds; } Maybe I'm just missing something basic, but I'm stuck. Any ideas? Thanks.

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• Are there concurrency problems when using -performSelector:withObject:afterDelay: ?

  - by mystify

  For example, I often use this: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:someDelay]; Now, lets say I call this 10 times to perform at the exact same delay, like: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; - (void)doSomethingAfterDelay:(id)someObject { /* access an array, read stuff, write stuff, do different things that would suffer in multithreaded environments .... all operations are nonatomic! */ } I have observed pretty strange behavior when doing things like this. For my understanding, this method schedules a timer to fire on the current thread, so in this case the main thread. But since it doesn't create new threads, it actually should not be possible to run into concurrency problems, right?

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• Are there concurrency problems when using -performSelector:withObject:afterDelay: ?

  - by mystify

  For example, I often use this: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:someDelay]; Now, lets say I call this 10 times to perform at the exact same delay, like: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; - (void)doSomethingAfterDelay:(id)someObject { /* access an array, read stuff, write stuff, do different things that would suffer in multithreaded environments .... all operations are nonatomic! */ } I have observed pretty strange behavior when doing things like this. For my understanding, this method schedules a timer to fire on the current thread, so in this case the main thread. But since it doesn't create new threads, it actually should not be possible to run into concurrency problems, right?

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• On-Demand Python Thread Start/Join Freezing Up from wxPython GUI

  - by HokieTux

  I'm attempting to build a very simple wxPython GUI that monitors and displays external data. There is a button that turns the monitoring on/off. When monitoring is turned on, the GUI updates a couple of wx StaticLabels with real-time data. When monitoring is turned off, the GUI idles. The way I tried to build it was with a fairly simple Python Thread layout. When the 'Start Monitoring' button is clicked, the program spawns a thread that updates the labels with real-time information. When the 'Stop Monitoring' button is clicked, thread.join() is called, and it should stop. The start function works and the real-time data updating works great, but when I click 'Stop', the whole program freezes. I'm running this on Windows 7 64-bit, so I get the usual "This Program has Stopped Responding" Windows dialog. Here is the relevant code: class MonGUI(wx.Panel): def __init__(self, parent): wx.Panel.__init__(self, parent) ... ... other code for the GUI here ... ... # Create the thread that will update the VFO information self.monThread = Thread(None, target=self.monThreadWork) self.monThread.daemon = True self.runThread = False def monThreadWork(self): while self.runThread: ... ... Update the StaticLabels with info ... (This part working) ... # Turn monitoring on/off when the button is pressed. def OnClick(self, event): if self.isMonitoring: self.button.SetLabel("Start Monitoring") self.isMonitoring = False self.runThread = False self.monThread.join() else: self.button.SetLabel("Stop Monitoring") self.isMonitoring = True # Start the monitor thread! self.runThread = True self.monThread.start() I'm sure there is a better way to do this, but I'm fairly new to GUI programming and Python threads, and this was the first thing I came up with. So, why does clicking the button to stop the thread make the whole thing freeze up?

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• How can I use SQL Server's full text search across multiple rows at once?

  - by Morbo

  I'm trying to improve the search functionality on my web forums. I've got a table of posts, and each post has (among other less interesting things): PostID, a unique ID for the individual post. ThreadID, an ID of the thread the post belongs to. There can be any number of posts per thread. Text, because a forum would be really boring without it. I want to write an efficient query that will search the threads in the forum for a series of words, and it should return a hit for any ThreadID for which there are posts that include all of the search words. For example, let's say that thread 9 has post 1001 with the word "cat" in it, and also post 1027 with the word "hat" in it. I want a search for cat hat to return a hit for thread 9. This seems like a straightforward requirement, but I don't know of an efficient way to do it. Using the regular FREETEXT and CONTAINS capabilities for N'cat AND hat' won't return any hits in the above example because the words exist in different posts, even though those posts are in the same thread. (As far as I can tell, when using CREATE FULLTEXT INDEX I have to give it my index on the primary key PostID, and can't tell it to index all posts with the same ThreadID together.) The solution that I currently have in place works, but sucks: maintain a separate table that contains the entire concatenated post text of every thread, and make a full text index on THAT. I'm looking for a solution that doesn't require me to keep a duplicate copy of the entire text of every thread in my forums. Any ideas? Am I missing something obvious?

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• VB.NET Program Locks Up with Internet Explorer Opened

  - by aaronsj

  I'm using Visual Studio 2008 and developing a VB.NET application. I'm having strange lockup problems with my program, but only when Internet explorer 8 is opened. When I cover my form with another window and then uncover it, I find that it has locked up. My program has no references to IE and the only thing it even has to do with IE is using Process.Start with a web address. My program works fine and exactly as it should, but only when IE is not opened. Does anyone know why a program would lock up only while IE is running? Edit: I've done some digging and I've found the offending thread in my program. I don't know what starts this thread or what it does, but when I kill it, my program no longer freezes. The thread is one of the CreateApplicationContext threads, here is the last few items in the stack trace of that thread. 6 ntkrnlpa.exe+0x897bc 7 ntdll.dll!KiFastSystemCallRet 8 mscorwrks.dll!LogHelp_TerminateOnAssert+0x61 9 mscorwrks.dll!DllUnregisterServerInternal+0x10523 10 mscorwrks.dll!DllUnregisterServerInternal+0x10542 11 mscorwrks.dll!StrongNameErrorInfo+0x34387 12 mscorwrks.dll!StrongNameErrorInfo+0x34815 13 mscorwrks.dll!CreateApplicationContext+0xbc35 14 KERNEL32.dll!GetModuleHandleA+0xdf Process explorer says my program is using no CPU nor throwing any exceptions while it is hung.

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• Separating code logic from the actual data structures. Best practices?

  - by Patrick

  I have an application that loads lots of data into memory (this is because it needs to perform some mathematical simulation on big data sets). This data comes from several database tables, that all refer to each other. The consistency rules on the data are rather complex, and looking up all the relevant data requires quite some hashes and other additional data structures on the data. Problem is that this data may also be changed interactively by the user in a dialog. When the user presses the OK button, I want to perform all the checks to see that he didn't introduce inconsistencies in the data. In practice all the data needs to be checked at once, so I cannot update my data set incrementally and perform the checks one by one. However, all the checking code work on the actual data set loaded in memory, and use the hashing and other data structures. This means I have to do the following: Take the user's changes from the dialog Apply them to the big data set Perform the checks on the big data set Undo all the changes if the checks fail I don't like this solution since other threads are also continuously using the data set, and I don't want to halt them while performing the checks. Also, the undo means that the old situation needs to be put aside, which is also not possible. An alternative is to separate the checking code from the data set (and let it work on explicitly given data, e.g. coming from the dialog) but this means that the checking code cannot use hashing and other additional data structures, because they only work on the big data set, making the checks much slower. What is a good practice to check user's changes on complex data before applying them to the 'application's' data set?

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• Create table class as a singleton

  - by Mark

  I got a class that I use as a table. This class got an array of 16 row classes. These row classes all have 6 double variables. The values of these rows are set once and never change. Would it be a good practice to make this table a singleton? The advantage is that it cost less memory, but the table will be called from multiple threads so I have to synchronize my code which way cause a bit slower application. However lookups in this table are probably a very small portion of the total code that is executed. EDIT: This is my code, are there better ways to do this or is this a good practice? Removed synchronized keyword according to recommendations in this question. final class HalfTimeTable { private HalfTimeRow[] table = new HalfTimeRow[16]; private static final HalfTimeTable instance = new HalfTimeTable(); private HalfTimeTable() { if (instance != null) { throw new IllegalStateException("Already instantiated"); } table[0] = new HalfTimeRow(4.0, 1.2599, 0.5050, 1.5, 1.7435, 0.1911); table[1] = new HalfTimeRow(8.0, 1.0000, 0.6514, 3.0, 1.3838, 0.4295); //etc } @Override @Deprecated public Object clone() throws CloneNotSupportedException { throw new CloneNotSupportedException(); } public static HalfTimeTable getInstance() { return instance; } public HalfTimeRow getRow(int rownumber) { return table[rownumber]; } }

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