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• Difference between performSelectorInBackground and NSOperation Subclass

  - by AmitSri

  I have created one testing app for running deep counter loop. I run the loop fuction in background thread using performSelectorInBackground and also NSOperation subclass separately. I am also using performSelectorOnMainThread to notify main thread within backgroundthread method and [NSNotificationCenter defaultCenter] postNotificationName within NSOperation subclass to notify main thread for updating UI. Initially both the implementation giving me same result and i am able to update UI without having any problem. The only difference i found is the Thread count between two implementations. The performSelectorInBackground implementation created one thread and got terminated after loop finished and my app thread count again goes to 1. The NSOperation subclass implementation created two new threads and keep exists in the application and i can see 3 threads after loop got finished in main() function. So, my question is why two threads created by NSOperation and why it didn't get terminated just like the first background thread implementation? I am little bit confuse and unable to decide which implementation is best in-terms of performance and memory management. Thanks

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• iphone Dev - activity indicator with NSThread not working on Nav controller table view

  - by Frames84

  I really can't get this to work, basically when my JSON feeds loads I want the indicator to show, then hide when it's stopped. It loads top level menu items 1st "Publishing, Broadcasting, Marketing Services", then when Broadcasting is selected it loads a feed using the JSON framework hosted on Google. Round this load I call startIndicator and stopIndicator using the NSThread. Have I missed something? @implementation GeneralNewsTableViewController @synthesize dataList; @synthesize generalNewsDetailViewController; @synthesize atLevel; -(void) startIndicator { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc ] init ]; [(UIActivityIndicatorView *)[self navigationItem].rightBarButtonItem.customView startAnimating]; [pool release]; } -(void) stopIndicator { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc ] init ]; [(UIActivityIndicatorView *)[self navigationItem].rightBarButtonItem.customView stopAnimating]; [pool release]; } - (void)viewDidLoad { NSMutableArray *checker = self.dataList; if(checker == nil) { self.title = NSLocalizedString(@"General1",@"General News"); NSMutableArray *array = [[NSArray alloc] initWithObjects:@"Publishing", @"Broadcasting",@"Marketing Services",nil]; self.dataList = [array retain]; self.atLevel = @"level1"; [array release]; } UIActivityIndicatorView * activityIndicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(0, 0, 20, 20)]; //set the initial property [activityIndicator stopAnimating]; [activityIndicator hidesWhenStopped]; //Create an instance of Bar button item with custome view which is of activity indicator UIBarButtonItem * barButton = [[UIBarButtonItem alloc] initWithCustomView:activityIndicator]; //Set the bar button the navigation bar [self navigationItem].rightBarButtonItem = barButton; //Memory clean up [activityIndicator release]; [barButton release]; [super viewDidLoad]; } - (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath { NSString *level = self.atLevel; if([level isEqualToString:@"level2"]) { return 70.0f; } else { return 40.0f; } } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *FirstLevelCell = @"FirstLevelCell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:FirstLevelCell]; if(cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:FirstLevelCell] autorelease]; } NSInteger row = [indexPath row]; NSString *level = self.atLevel; if([level isEqualToString:@"level2"]) { NSMutableArray *stream = [self.dataList objectAtIndex:row]; NSString *newsTitle = [stream valueForKey:@"title"]; if( ![newsTitle isKindOfClass:[NSString class]] ) { cell.textLabel.text = @""; } else { cell.textLabel.text = [stream valueForKey:@"title"]; } cell.textLabel.numberOfLines = 2; cell.textLabel.font =[UIFont systemFontOfSize:10]; cell.detailTextLabel.numberOfLines = 1; cell.detailTextLabel.font= [UIFont systemFontOfSize:8]; cell.detailTextLabel.text = [stream valueForKey:@"created"]; NSData *imageURL = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:@"http://www.how-do.co.uk/images/stories/Cimex.jpg"]]; UIImage *newsImage = [[UIImage alloc] initWithData:imageURL]; cell.imageView.image = newsImage; [imageURL release]; [newsImage release]; } else { cell.textLabel.text = [dataList objectAtIndex:row]; } return cell; } - (void) tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { NSUInteger row = [indexPath row]; NSMutableString *levelType = (NSMutableString *) [dataList objectAtIndex:row]; if(![levelType isKindOfClass:[NSString class]]) { if(self.generalNewsDetailViewController == nil) { GeneralNewsDetailViewController *generalDetail = [[GeneralNewsDetailViewController alloc] initWithNibName:@"GeneralNewsDetailView" bundle:nil]; self.generalNewsDetailViewController = generalDetail; [generalDetail release]; } NSDictionary *stream = [self.dataList objectAtIndex:row]; NSString *newsTitle = [stream valueForKey:@"title"]; if( ![newsTitle isKindOfClass:[NSString class]] ) { generalNewsDetailViewController.newsTitle = @""; } else { generalNewsDetailViewController.newsTitle =[stream valueForKey:@"title"]; } generalNewsDetailViewController.newsId = [stream valueForKey:@"id"]; generalNewsDetailViewController.fullText = [stream valueForKey:@"fulltext"]; generalNewsDetailViewController.newsImage = [stream valueForKey:@"images"]; generalNewsDetailViewController.created = [stream valueForKey:@"created"]; HowDo_v1AppDelegate *delegate = [[UIApplication sharedApplication] delegate]; [delegate.generalNewsNavController pushViewController:self.generalNewsDetailViewController animated:YES]; } else { GeneralNewsTableViewController *generalSubDetail = [[GeneralNewsTableViewController alloc] initWithNibName:@"GeneralNewsTableView" bundle:nil]; NSMutableArray *array; NSString *titleSelected = (NSString *) [dataList objectAtIndex:row]; if([titleSelected isEqualToString:@"Publishing"]) { generalSubDetail.title = @"Publishing news detail"; array = [[NSArray alloc] initWithObjects:@"pub News1", @"pub News2",@"pub News3",nil]; generalSubDetail.atLevel = @"level1"; } else if ([titleSelected isEqualToString:@"Broadcasting"]) { generalSubDetail.title = @"Broadcasting news detail"; /// START [self performSelectorOnMainThread:@selector(startIndicator) withObject:nil waitUntilDone:YES]; if(jSONDataAccessWrapper == nil) { jSONDataAccessWrapper = [JSON_DataAccess_Wrapper alloc]; } array = [jSONDataAccessWrapper downloadJSONFeed]; [self performSelectorOnMainThread:@selector(stopIndicator) withObject:nil waitUntilDone:YES]; generalSubDetail.atLevel = @"level2"; } else if ([titleSelected isEqualToString:@"Marketing Services"]) { generalSubDetail.title = @"Marketing Services news detail"; array = [[NSArray alloc] initWithObjects:@"Marketing News1", @"Marketing News2",@"Marketing News3",nil]; generalSubDetail.atLevel = @"level1"; } generalSubDetail.dataList = array; [self.navigationController pushViewController:generalSubDetail animated:YES]; [titleSelected release]; } } - (NSInteger)tableView:(UITableView *)table numberOfRowsInSection:(NSInteger)section //- (NSInteger) tableView:(UITableView *)tableView numberOfRowsInSection:(NSIndexPath *) section { return [self.dataList count]; } Cheers for any feedback Frames

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• Loading a dll from a dll ?

  - by Quandary

  What's the best way for loading a dll from a dll ? My problem is I can't load a dll on process_attach, and I cannot load the dll from the main program, because I don't control the main program source. And therefore I cannot call a non-dllmain function, too.

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• Spawning BackgroundWorkers

  - by washtik

  We have a business case that would be perfect for multiple BackgroundWorkers. As an example, we have a form with a "Save" button on it. Normally we would run all the save commands (Save is an example) synchronously and then close the form. We would like to now split the work onto separate threads using backgroundworker. We will loop through each "Save" required (could be many and/or different number of commands that need executing) creating a BackgroundWorker for each command required. The question is ... how do we wait for ALL the BackgroundWorkers to complete before we close the form. We understand how to wait for a single BackgroundWorker to complete but when we have X number of BackgroundWorkers operating, how do we wait until all are complete before closing the UI form?

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• Android AsyncTask context problem, help!

  - by dnkoutso

  I've been working with AsyncTasks in Android and I am dealing with a strange issue. Take a simple example, an Activity with one AsyncTask. The task on the background does not do anything spectacular, it just sleeps for 8 seconds. At the end of the AsyncTask in the onPostExecute() method I am just setting a button visibility status to View.VISIBLE, only to verify my results. Now, this works great until the user decides to change his phones orientation while the AsyncTask is working (within the 8 second sleep window). I understand the Android activity life cycle and I know the activity gets destroyed and recreated. This is where the problem comes in. The AsyncTask is referring to a button and apparently holds a reference to the context that started the AsyncTask in the first place. I would expect, that this old context (since the user caused an orientation change) to either become null and the AsyncTask to throw an NPE for the reference to the button it is trying to make visible. Instead, no NPE is thrown, the asynctask thinks that the button reference is not null, sets it to visible. The result? Nothing is happening on the screen! I have tackled this by keeping and updating the context reference into the AsyncTask. This is cumbersome and prone to leaks. Here's the code: public class Main extends Activity { private Button mButton = null; private Button mTestButton = null; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mButton = (Button) findViewById(R.id.btnStart); mButton.setOnClickListener(new OnClickListener () { @Override public void onClick(View v) { new taskDoSomething().execute(0l); } }); mTestButton = (Button) findViewById(R.id.btnTest); } private class taskDoSomething extends AsyncTask<Long, Integer, Integer> { @Override protected Integer doInBackground(Long... params) { Log.i("LOGGER", "Starting..."); try { Thread.sleep(8000); } catch (InterruptedException e) { e.printStackTrace(); } return 0; } @Override protected void onPostExecute(Integer result) { Log.i("LOGGER", "...Done"); mTestButton.setVisibility(View.VISIBLE); } } } Try executing and while the AsyncTask is working change your phones orientation.

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• Accessing UI context from asynch task

  - by cdonner

  I came across this android example that runs an AsyncTask from a UI thread. The class ExportDatabaseTask is declared and instantiated in the Activity, and apparently it is possible to reference the activity's UI context from the onPreExecute and onPostExecute events, like this: public class ManageData extends Activity { private ExportDatabaseTask exportDatabaseTask; [...] @Override public void onCreate(final Bundle savedInstanceState) { [...] ManageData.this.exportDatabaseTask = new ExportDatabaseTask(); ManageData.this.exportDatabaseTask.execute(); [...] } private class ExportDatabaseTask extends AsyncTask<String, Void, Boolean> { private final ProgressDialog dialog = new ProgressDialog(ManageData.this); protected void onPreExecute() { this.dialog.setMessage("Exporting database..."); this.dialog.show(); } protected Boolean doInBackground(final String... args) { [...] } protected void onPostExecute(final Boolean success) { if (this.dialog.isShowing()) { this.dialog.dismiss(); } } } I am trying to refactor this so that the ExportDatabaseTask is declared in another class that is not the Activity, for various reasons, and I can't quite figure out how to make it work. I am lacking some basic Java concepts here, which I readily admit. Specifically, myActivity is null in onPreExecute(). Why is that? public void onClick(View v) { Exporter ex = new Exporter(getApplicationContext(), ActivityMain.this); ex.exportDatabaseTask.execute(); } public class Exporter { public ExportDatabaseTask exportDatabaseTask; public Exporter(Context ctx, ActivityMain act) { myContext = ctx; myActivity = act; this.exportDatabaseTask = new ExportDatabaseTask(); } public class ExportDatabaseTask extends AsyncTask<Void, Void, Boolean> { private final ProgressDialog dialog = new ProgressDialog(myContext); // can use UI thread here? protected void onPreExecute() { // ====> this throws a Nullpointer exception: myActivity.dialog.setMessage("Exporting database..."); myActivity.dialog.show(); } protected Boolean doInBackground(final Void... args) { } protected void onPostExecute(final Boolean success) { if (myActivity.dialog.isShowing()) { myActivity.dialog.dismiss(); } } } }

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• Delegate, BeginInvoke. EndInvoke - How to clean up multiple Async threat calls to the same delegate?

  - by Dan

  I've created a Delegate that I intend to call Async. Module Level Delegate Sub GetPartListDataFromServer(ByVal dvOriginal As DataView, ByVal ProgramID As Integer) Dim dlgGetPartList As GetPartListDataFromServer The following code I use in a method Dim dlgGetPartList As New GetPartListDataFromServer(AddressOf AsyncThreadMethod_GetPartListDataFromServer) dlgGetPartList.BeginInvoke(ucboPart.DataSource, ucboProgram.Value, AddressOf AsyncCallback_GetPartListDataFromServer, Nothing) The method runs and does what it needs to The Asyn callback is fired upon completion where I do an EndInvoke Sub AsyncCallback_GetPartListDataFromServer(ByVal ar As IAsyncResult) dlgGetPartList.EndInvoke(Nothing) End Sub It works as long as the method that starts the BeginInvoke on the delegate only ever runs while there is not a BeginInvoke/Thread operation already running. Problem is that the a new thread could be invoked while another thread on the delegate is still running and hasnt yet been EndInvoke'd. The program needs to be able to have the delegate run in more than one instance at a time if necessary and they all need to complete and have EndInvoke called. Once I start another BeginInvoke I lose the reference to the first BeginInvoke so I am unable to clean up the new thread with an EndInvoke. What is a clean solution and best practice to overcome this problem?

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• Cross-thread Winforms control editing

  - by Motig

  Hey, how can I edit the text in a windows form element if the code that is editing the text 'belongs' to a seperate thread from the one that contains the windows form? I get the exception: Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on. Thank you.

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• Calculate time of method execution and send to WCF service async

  - by Tim

  I need to implement time calculation for repository methods in my asp .net mvc project classes. The problem is that i need to send time calculation data to WCF Service which is time consuming. I think about threads which can help to cal WCF service asynchronously. But I have very little experience with it. Do I need to create new thread each time or I can create a global thread, if so then how? I have something like that: StopWatch class public class StopWatch { private DateTime _startTime; private DateTime _endTime; public void Start() { _startTime = DateTime.Now; } protected void StopTimerAndWriteStatistics() { _endTime = DateTime.Now; TimeSpan timeResult = _endTime - _startTime; //WCF proxy object var reporting = AppServerUtility.GetProxy<IReporting>(); //Send data to server reporting.WriteStatistics(_startTime, _endTime, timeResult, "some information"); } public void Stop() { //Here is the thread I have question with var thread = new Thread(StopTimerAndWriteStatistics); thread.Start(); } } Using of StopWatch class in Repository public class SomeRepository { public List<ObjectInfo> List() { StopWatch sw = new StopWatch(); sw.Start(); //performing long time operation sw.Stop(); } } What am I doing wrong with threads?

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• No output from exception

  - by Grasper

  Why does this code not print an exception stack trace? import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; public class Playground { /** * @param args */ public static void main(String[] args) { startThread(); } private static void startThread() { ScheduledExecutorService timer = Executors .newSingleThreadScheduledExecutor(); Runnable r = new Runnable() { int dummyInt = 0; boolean dummyBoolean = false; @Override public void run() { dummyInt = Integer.parseInt("AAAA"); if (dummyBoolean) { dummyBoolean= false; } else { dummyBoolean= true; } } }; timer.scheduleAtFixedRate(r, 0, 100, TimeUnit.MILLISECONDS); } } How can I get it to? I would expect to see this: java.lang.NumberFormatException: For input string: "AAAA" at java.lang.NumberFormatException.forInputString(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at java.lang.Integer.parseInt(Unknown Source) at Playground$1.run(Playground.java:25) at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.util.concurrent.FutureTask$Sync.innerRunAndReset(Unknown Source) at java.util.concurrent.FutureTask.runAndReset(Unknown Source) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$101(Unknown Source) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.runPeriodic(Unknown Source) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source)

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• Is there a way to synchronize Silverlight Child Window (make it like MessageBox)?

  - by Dmitriy

  ChildWindow1 wnd1 = new ChildWindow1(); ChildWindow2 wnd2 = new ChildWindow2(); wnd1.Show(); //**Is there a way to pause thread here until wnd1 is closed???** wnd2.Show();

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• Trace/BPT trap when running feedparser inside a Thread object

  - by simao

  Hello, I am trying to run a Thread to parse a list of links using the universal feed parser, but when I start the thread I get a Trace/BPT trap. Here's the code I am using: class parseRssFiles(Thread): def __init__ (self,rssLinks): Thread.__init__(self) self.rssLinks = rssLinks def run(self): self.rssContents = [ feedparser.parse(link) for link in rssLinks] Is there any other way to do this? Link to the report generated by Mac OS X 10.6.2: http://simaom.com/trace.txt Thanks

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• Changing html <-> ajax <-> php/mysql to threaded approach

  - by Saif Bechan

  I have an application that needs to be updated real-time. There are various counters and other information that have to come from the database and the system needs to be up to date for the user. My approach now is just a normal ajax request every second to get the new values from the database. There is a JavaScript which loops every second getting the values trough ajax. This works fine but I think its very inefficient. The problem There is an ajax script that loops every second requesting data from php # On the server it has to load the PHP interpeter The PHP file has to get the data and format it correctly # PHP has to make a connection with the mysql database Work with the database(reads,never writes) Format the data so it can be send Send the data back to the browser # Close the database connection, and close the php interpeter Last the browser has to read these values and update the various html parts Now with this approach it has to load the interpreter and make a db connection every second. I was thinking of a way to make this more efficient, and maybe use a threaded approach to this. Threaded aprouch Do a post to the PHP when you enter the page and keep the connection alive In PHP only load the interpreter once, and make a connection to the DB ones Every second send an ajax response to the javascript listener The javascript listener than just changes values as the response from php arrives. I think this approach will be a great optimization to the server load and overall performance. But I can spot some weak point in the system and i need some help with these. Problems with the approach PHP execution time limit I don't think PHP is designed for such a setup. I know there is a time limit on php script execution. I don't know if an everlasting loop in PHP will cause any serious cpu/memory problems. Sending ajax request without breaking I don't know if it is possible to have just one ajax post action and have open and accepting data. user exists the page What will happen when the user exists the page and the PHP script is still going. Will it go on forever. security issues so far i can't think of any security issues. Almost every setup you use have some security issues. Maybe there are some with this solution I do not know of. Open to other solution I really want to change the setup as it is now and move to a threaded approach or better. If someone has a better approach to tackle this I definitely want to hear that. Maybe the usage of some other scripts is better suited for having an ongoing runtime. I only know php and java so any suggestions are welcome and I am willing to dig trough. I know there are things like perl, python etcetera that are used for this type of threaded but i don't know which one is best suited. When using other script If the best way is to go with other type of script like perl,python etcetera I do have some critera. The script has to be accessible via ajax post If it accepts some kind of json encode/decode it would be nice The script has to be able to access the session file This is essential because I need to know if the user is logged in The script has to be able to easily talk to MySQL All comments are welcome, and I hope this question is helpful to other also. Cheers!

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• iPhone: NSOperationQueue running operations serially

  - by Greg Maletic

  I have a singleton NSOperationQueue that handles all of my network requests. I'm noticing, however, that when I have one particularly long operation running (this particular operation takes at least 25 seconds), my other operations don't run until it completes. maxConcurrentOperationCount is set to NSOperationQueueDefaultMaxConcurrentOperationCount, so I don't believe that's the issue. Any reason why this would be happening? Besides spawning multiple NSOperationQueues (a solution that I'm not sure would work, nor am I sure it's a good idea), what's the best way to fix this problem? Thanks.

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• Subclassing a window from a thread in c#

  - by user258651

  I'm creating a thread that looks for a window. When it finds the window, it overrides its windowproc, and handles WM_COMMAND and WM_CLOSE. Here's the code that looks for the window and subclasses it: public void DetectFileDialogProc() { Window fileDialog = null; // try to find the dialog twice, with a delay of 500 ms each time for (int attempts = 0; fileDialog == null && attempts < 2; attempts++) { // FindDialogs enumerates all windows of class #32770 via an EnumWindowProc foreach (Window wnd in FindDialogs(500)) { IntPtr parent = NativeMethods.User32.GetParent(wnd.Handle); if (parent != IntPtr.Zero) { // we're looking for a dialog whose parent is a dialog as well Window parentWindow = new Window(parent); if (parentWindow.ClassName == NativeMethods.SystemWindowClasses.Dialog) { fileDialog = wnd; break; } } } } // if we found the dialog if (fileDialog != null) { OldWinProc = NativeMethods.User32.GetWindowLong(fileDialog.Handle, NativeMethods.GWL_WNDPROC); NativeMethods.User32.SetWindowLong(fileDialog.Handle, NativeMethods.GWL_WNDPROC, Marshal.GetFunctionPointerForDelegate(new WindowProc(WndProc)).ToInt32()); } } And the windowproc: public IntPtr WndProc(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam) { lock (this) { if (!handled) { if (msg == NativeMethods.WM_COMMAND || msg == NativeMethods.WM_CLOSE) { // adding to a list. i never access the window via the hwnd from this list, i just treat it as a number _addDescriptor(hWnd); handled = true; } } } return NativeMethods.User32.CallWindowProc(OldWinProc, hWnd, msg, wParam, lParam); } This all works well under normal conditions. But I am seeing two instances of bad behavior in order of badness: If I do not close the dialog within a minute or so, the app crashes. Is this because the thread is getting garbage collected? This would kind of make sense, as far as GC can tell the thread is done? If this is the case, (and I don't know that it is), how can I make the thread stay around as long as the dialog is around? If I immediately close the dialog with the 'X' button (WM_CLOSE) the app crashes. I believe its crashing in the windowproc, but I can't get a breakpoint in there. I'm getting an AccessViolationException, The exception says "Attempted to read or write protected memory. This is often an indication that other memory is corrupt." Its a race condition, but of what I don't know. FYI, I had been reseting the old windowproc once I processed the commands, but that was crashing even more often! Any ideas on how I can solve these issues?

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• [C++] Producer/Consumer Implementation -- Feedback Wanted

  - by bobber205

  I'm preparing for an interview in a few weeks and I thougth I would give threads in boost a go, as well as do the simple producer/consumer problem I learned in school. Haven't done it quite awhile so I was curious what you guys think of this? What should I add to make it a better example etc. Thanks for the feedback! :) ////////////////////////////////////////////////////////////////////////// boost::mutex bufferMutex; deque<int> buffer; const int maxBufferSize = 5; ////////////////////////////////////////////////////////////////////////// bool AddToBuffer(int i) { if (buffer.size() < maxBufferSize) { buffer.push_back(i); return true; } else { return false; } } bool GetFromBuffer(int& toReturn) { if (buffer.size() == 0) { return false; } else { toReturn = buffer[buffer.size()-1]; buffer.pop_back(); return true; } } struct Producer { int ID; void operator()() { while (true) { boost::mutex::scoped_lock lock(bufferMutex); int num = dice(); bool result = AddToBuffer(num); lock.unlock(); //safe area done if (result) { cout << "Producer " << this->ID << " Added " << num << endl; } else { cout << "!!Buffer was Full!!" << endl; } //Added //Now wait boost::xtime xt; xtime_get( &xt, boost::TIME_UTC); xt.nsec += 1000000 + 100000 * (rand() % 1000); boost::thread::sleep(xt); } } }; struct Consumer { int ID; void operator()() { while (true) { int returnedInt = 0; boost::mutex::scoped_lock lock(bufferMutex); bool result = GetFromBuffer(returnedInt); lock.unlock(); //safe area done if (result) { cout << "\tConsumer " << this->ID << " Took Out " << returnedInt << endl; } else { cout << "!!Buffer was Empty!!" << endl; } //Added //Now wait boost::xtime xt; xtime_get( &xt, boost::TIME_UTC); xt.nsec += 1000000 + 100000 * (rand() % 1000); boost::thread::sleep(xt); } } }; void main() { Producer p, p2; Consumer c, c2; p.ID = 1; p2.ID = 2; c.ID = 1; c2.ID = 2; boost::thread thread1(boost::ref(p)); boost::thread thread2(boost::ref(c)); boost::thread thread3(boost::ref(p2)); boost::thread thread4(boost::ref(c2)); int x; cin >> x; }

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• Python Socket Getting Connection Reset

  - by Ian

  I created a threaded socket listener that stores newly accepted connections in a queue. The socket threads then read from the queue and respond. For some reason, when doing benchmarking with 'ab' (apache benchmark) using a concurrency of 2 or more, I always get a connection reset before it's able to complete the benchmark (this is taking place locally, so there's no external connection issue). class server: _ip = '' _port = 8888 def __init__(self, ip=None, port=None): if ip is not None: self._ip = ip if port is not None: self._port = port self.server_listener(self._ip, self._port) def now(self): return time.ctime(time.time()) def http_responder(self, conn, addr): httpobj = http_builder() httpobj.header('HTTP/1.1 200 OK') httpobj.header('Content-Type: text/html; charset=UTF-8') httpobj.header('Connection: close') httpobj.body("Everything looks good") data = httpobj.generate() sent = conn.sendall(data) def http_thread(self, id): self.log("THREAD %d: Starting Up..." % id) while True: conn, addr = self.q.get() ip, port = addr self.log("THREAD %d: responding to request: %s:%s - %s" % (id, ip, port, self.now())) self.http_responder(conn, addr) self.q.task_done() conn.close() def server_listener(self, host, port): self.q = Queue.Queue(0) sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.bind( (host, port) ) sock.listen(5) for i in xrange(4): #thread count thread.start_new(self.http_thread, (i+1, )) while True: self.q.put(sock.accept()) sock.close() server('', 9999) When running the benchmark, I get totally random numbers of good requests before it errors out, usually between 4 and 500. Edit: Took me a while to figure it out, but the problem was in sock.listen(5). Because I was using apache benchmark with a higher concurrency (5 and up) it was causing the backlog of connections to pile up, at which point the connections started getting dropped by the socket.

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• Python MD5 Hash Faster Calculation

  - by balgan

  Hi everyone. I will try my best to explain my problem and my line of thought on how I think I can solve it. I use this code for root, dirs, files in os.walk(downloaddir): for infile in files: f = open(os.path.join(root,infile),'rb') filehash = hashlib.md5() while True: data = f.read(10240) if len(data) == 0: break filehash.update(data) print "FILENAME: " , infile print "FILE HASH: " , filehash.hexdigest() and using start = time.time() elapsed = time.time() - start I measure how long it takes to calculate an hash. Pointing my code to a file with 653megs this is the result: root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.624 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.373 root@Mars:/home/tiago# python algorithm-timer.py FILENAME: freebsd.iso FILE HASH: ace0afedfa7c6e0ad12c77b6652b02ab 12.540 Ok now 12 seconds +- on a 653mb file, my problem is I intend to use this code on a program that will run through multiple files, some of them might be 4/5/6Gb and it will take wayy longer to calculate. What am wondering is if there is a faster way for me to calculate the hash of the file? Maybe by doing some multithreading? I used a another script to check the use of the CPU second by second and I see that my code is only using 1 out of my 2 CPUs and only at 25% max, any way I can change this? Thank you all in advance for the given help.

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• Unreferenced Thread object dispose

  - by Benny

  If i use thread like this: void foo() { new Thread().Start(); } since the Thread object is not referenced, will it be disposed by GC before the designated work is done?

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• What are the differences between currently executing .NET thread and Win32 thread

  - by Ybbest

  I am reading the Asp.net security documentation on msdn.I come across these tow terms and get really confused. # WindowsIdentity = WindowsIdentity.GetCurrent() which returns the identity of the security context of the currently executing Win32 thread. # Thread = Thread.CurrentPrincipal which returns the principal of the currently executing .NET thread which rides on top of the Win32 thread.

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• Linux's thread local storage implementation

  - by anon

  __thread Foo foo; How is "foo" actually resolved? Does the compiler silently replace every instance of "foo" with a function call? Is "foo" stored somewhere relative to the bottom of the stack, and the compiler stores this as "hey, for each thread, have this space near the bottom of the stack, and foo is stored as 'offset x from bottom of stack'"?

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• objective-c : @synchronized how it works ?

  - by g.revolution

  Hi, i have two methods -(void) a { @synchronized(self) { // critical section 1 } } -(void) b { @synchronized(self) { // critical section 2 } } now my question is if a thread is in critical section 1. will the critical section 2 be locked for other threads or other threads can access critical section 2.

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• What's wrong with my cross-thread call in Windows Forms?

  - by MainMa

  Hi, I encounter a problem with a Windows Forms application. A form must be displayed from another thread. So in the form class, I have the following code: private delegate void DisplayDialogCallback(); public void DisplayDialog() { if (this.InvokeRequired) { this.Invoke(new DisplayDialogCallback(DisplayDialog)); } else { this.ShowDialog(); } } Now, every time I run this, an InvalidOperationException is thrown on the line this.ShowDialog();: "Cross-thread operation not valid: Control 'SampleForm' accessed from a thread other than the thread it was created on." What's wrong with this piece of code? Isn't it a valid way to make cross-thread calls? Is there something special with ShowDialog()?

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• UdpClient receiving and sending at the same time

  - by SoMoS

  Hello, I am maintaining other's code and its using the class UdpClient. The code declares one instance of UdpClient and receives data continuosly using the UdpClient.Receive(). When data is received it is processed in another thread and the UdpClient calls Receive() again. At the same time when the data is processed the same client is sending a response back. Question: Is this a bug? I think so because UdpClient is not thread safe so you can not call two methods at the same time. Anyways code is working fine but ...

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• Scala actors: receive vs react

  - by jqno

  Let me first say that I have quite a lot of Java experience, but have only recently become interested in functional languages. Recently I've started looking at Scala, which seems like a very nice language. However, I've been reading about Scala's Actor framework in Programming in Scala, and there's one thing I don't understand. In chapter 30.4 it says that using react instead of receive makes it possible to re-use threads, which is good for performance, since threads are expensive in the JVM. Does this mean that, as long as I remember to call react instead of receive, I can start as many Actors as I like? Before discovering Scala, I've been playing with Erlang, and the author of Programming Erlang boasts about spawning over 200,000 processes without breaking a sweat. I'd hate to do that with Java threads. What kind of limits am I looking at in Scala as compared to Erlang (and Java)? Also, how does this thread re-use work in Scala? Let's assume, for simplicity, that I have only one thread. Will all the actors that I start run sequentially in this thread, or will some sort of task-switching take place? For example, if I start two actors that ping-pong messages to each other, will I risk deadlock if they're started in the same thread? According to Programming in Scala, writing actors to use react is more difficult than with receive. This sounds plausible, since react doesn't return. However, the book goes on to show how you can put a react inside a loop using Actor.loop. As a result, you get loop { react { ... } } which, to me, seems pretty similar to while (true) { receive { ... } } which is used earlier in the book. Still, the book says that "in practice, programs will need at least a few receive's". So what am I missing here? What can receive do that react cannot, besides return? And why do I care? Finally, coming to the core of what I don't understand: the book keeps mentioning how using react makes it possible to discard the call stack to re-use the thread. How does that work? Why is it necessary to discard the call stack? And why can the call stack be discarded when a function terminates by throwing an exception (react), but not when it terminates by returning (receive)? I have the impression that Programming in Scala has been glossing over some of the key issues here, which is a shame, because otherwise it's a truly excellent book.

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