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• A circular character buffer

  A circular, thread-safe read/write character buffer

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• Web Service Example - Part 3: Asynchronous

  - by Denis T

  In this edition of the ADF Mobile blog we'll tackle part 3 of our Web Service examples.  In this posting we'll take a look at firing the web service asynchronously and then filling in the UI when it completes.  This can be useful when you have data on the device in a local store and want to show that to the user while the application uses lazy loading from a web service to load more data. Getting the sample code: Just click here to download a zip of the entire project.  You can unzip it and load it into JDeveloper and deploy it either to iOS or Android.  Please follow the previous blog posts if you need help getting JDeveloper or ADF Mobile installed.  Note: This is a different workspace than WS-Part2 What's different? In this example, when you click the Search button on the Forecast By Zip option, now it takes you directly to the results page, which is initially blank.  When the web service returns a second or two later the data pops into the UI.  If you go back to the search page and hit Search it will again clear the results and invoke the web service asynchronously.  This isn't really that useful for this particular example but it shows an important technique that can be used for other use cases. How it was done 1)  First we created a new class, ForecastWorker, that implements the Runnable interface.  This is used as our worker class that we create an instance of and pass to a new thread that we create when the Search button is pressed inside the retrieveForecast actionListener handler.  Once the thread is started, the retrieveForecast returns immediately.  2)  The rest of the code that we had previously in the retrieveForecast method has now been moved to the retrieveForecastAsync.  Note that we've also added synchronized specifiers on both these methods so they are protected from re-entrancy. 3)  The run method of the ForecastWorker class then calls the retrieveForecastAsync method.  This executes the web service code that we had previously, but now on a separate thread so the UI is not locked.  If we had already shown data on the screen it would have appeared before this was invoked.  Note that you do not see a loading indicator either because this is on a separate thread and nothing is blocked. 4)  The last but very important aspect of this method is that once we update data in the collections from the data we retrieve from the web service, we call AdfmfJavaUtilities.flushDataChangeEvents().   We need this because as data is updated in the background thread, those data change events are not propagated to the main thread until you explicitly flush them.  As soon as you do this, the UI will get updated if any changes have been queued. Summary of Fundamental Changes In This Application The most fundamental change is that we are invoking and handling our web services in a background thread and updating the UI when the data returns.  This allows an application to provide a better user experience in many cases because data that is already available locally is displayed while lengthy queries or web service calls can be done in the background and the UI updated when they return.  There are many different use cases for background threads and this is just one example of optimizing the user experience and generating a better mobile application. 

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• Do threads delete themselves?

  - by Prog

  Let's say I was working on a Swing application. Most of it is run on the EDT using SwingUtilities.invokeLater() inside the main method, because I heard (please correct me if I'm wrong) that that's what you need to do with Swing. However, some parts of it shouldn't run on the EDT. These parts are parts that take long to complete (I assume that this is because long tasks on the EDT will interfere with GUI stuff the EDT should be doing, and thus these kinds of tasks should be run on parallel, on a different thread. Is this assumption correct?) To do this, when I need to perform a task that takes long to complete and thus can't be run on the EDT like the rest of the program, I create a new thread and run that task inside it. My question is: When the run() method of that new thread finishes, aka the thread finished it's job. Does it delete itself? Or does it keep existing in the memory?

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• Threads slowing down application and not working properly

  - by Belgin

  I'm making a software renderer which does per-polygon rasterization using a floating point digital differential analyzer algorithm. My idea was to create two threads for rasterization and have them work like so: one thread draws each even scanline in a polygon and the other thread draws each odd scanline, and they both start working at the same time, but the main application waits for both of them to finish and then pauses them before continuing with other computations. As this is the first time I'm making a threaded application, I'm not sure if the following method for thread synchronization is correct: First of all, I use two global variables to control the two threads, if a global variable is set to 1, that means the thread can start working, otherwise it must not work. This is checked by the thread running an infinite loop and if it detects that the global variable has changed its value, it does its job and then sets the variable back to 0 again. The main program also uses an empty while to check when both variables become 0 after setting them to 1. Second, each thread is assigned a global structure which contains information about the triangle that is about to be rasterized. The structures are filled in by the main program before setting the global variables to 1. My dilemma is that, while this process works under some conditions, it slows down the program considerably, and also it fails to run properly when compiled for Release in Visual Studio, or when compiled with any sort of -O optimization with gcc (i.e. nothing on screen, even SEGFAULTs). The program isn't much faster by default without threads, which you can see for yourself by commenting out the #define THREADS directive, but if I apply optimizations, it becomes much faster (especially with gcc -Ofast -march=native). N.B. It might not compile with gcc because of fscanf_s calls, but you can replace those with the usual fscanf, if you wish to use gcc. Because there is a lot of code, too much for here or pastebin, I created a git repository where you can view it. My questions are: Why does adding these two threads slow down my application? Why doesn't it work when compiling for Release or with optimizations? Can I speed up the application with threads? If so, how? Thanks in advance.

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• Issues with time slicing

  - by user12331

  I was trying to see the effect of time slicing. And how it can consume significant amount of time. Actually, I was trying to divide a certain work into number of threads and see the effect. I have a two core processor. So two threads can run in parallel. I was trying to see if I have a work w that is done by 2 threads, and if I have the same work done by t threads with each thread doing w/t of the work. How much does time slicing play a role in it As time slicing is time consuming process, I was expecting that when I do the same work using a two thread process or by a t thread process, the amount of time taken by the t thread process will be more Any suggestions?

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• Can't open display: :0

  - by empec

  I'm trying to get Nexus Mod Manager (Beta yet) working on wine, but after the configuration of NMM it crashes with an error. During the startup it spams alot of terminal stuff and at the end I find this error. ###!!! ABORT: Main-thread-only object used off the main thread: file /build/wine-mozilla-1.8/xpcom/base/nsCycleCollector.cpp, line 1166 ###!!! ABORT: Main-thread-only object used off the main thread: file /build/wine-mozilla-1.8/xpcom/base/nsCycleCollector.cpp, line 1166 Maximum number of clients reachederr:winediag:x11drv_init_thread_data x11drv: Can't open display: :0. Please ensure that your X server is running and that $DISPLAY is set correctly. Any suggestions? Thanks!

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• How should I implement multiple threads in a game? [duplicate]

  - by xerwin

  This question already has an answer here: Multi-threaded games best practices. One thread for 'logic', one for rendering, or more? 6 answers So I recently started learning Java, and having a interest in playing games as well as developing them, naturally I want to create game in Java. I have experience with games in C# and C++ but all of them were single-threaded simple games. But now, I learned how easy it is to make threads in Java, I want to take things to the next level. I started thinking about how would I actually implement threading in a game. I read couple of articles that say the same thing "Usually you have thread for rendering, for updating game logic, for AI, ..." but I haven't (or didn't look hard enough) found example of implementation. My idea how to make implementation is something like this (example for AI) public class AIThread implements Runnable{ private List<AI> ai; private Player player; /*...*/ public void run() { for (int i = 0; i < ai.size(); i++){ ai.get(i).update(player); } Thread.sleep(/* sleep until the next game "tick" */); } } I think this could work. If I also had a rendering and updating thread list of AI in both those threads, since I need to draw the AI and I need to calculate the logic between player and AI(But that could be moved to AIThread, but as an example) . Coming from C++ I'm used to do thing elegantly and efficiently, and this seems like neither of those. So what would be the correct way to handle this? Should I just keep multiple copies of resources in each thread or should I have the resources on one spot, declared with synchronized keyword? I'm afraid that could cause deadlocks, but I'm not yet qualified enough to know when a code will produce deadlock.

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• c# opennetCF background worker - e.result gives a ObjectDisposedException

  - by ikky

  Hi! I'm new working with background worker in C#. Here is a class, and under it, you will find the instansiation of it, and under there i will define my problem for you: I have the class Drawing: class Drawing { BackgroundWorker bgWorker; ProgressBar progressBar; Panel panelHolder; public Drawing(ref ProgressBar pgbar, ref Panel panelBig) // Progressbar and panelBig as reference { this.panelHolder = panelBig; this.progressBar = pgbar; bgWorker = new BackgroundWorker(); bgWorker.WorkerReportsProgress = true; bgWorker.WorkerSupportsCancellation = true; bgWorker.DoWork += new OpenNETCF.ComponentModel.DoWorkEventHandler(this.bgWorker_DoWork); bgWorker.RunWorkerCompleted += new OpenNETCF.ComponentModel.RunWorkerCompletedEventHandler(this.bgWorker_RunWorkerCompleted); bgWorker.ProgressChanged += new OpenNETCF.ComponentModel.ProgressChangedEventHandler(this.bgWorker_ProgressChanged); } public void createDrawing() { bgWorker.RunWorkerAsync(); } private void bgWorker_DoWork(object sender, DoWorkEventArgs e) { Panel panelContainer = new Panel(); // Adding panels to the panelContainer for(i=0; i<100; i++) { Panel panelSubpanel = new Panel(); // Setting size, color, name etc.... panelContainer.Controls.Add(panelSubpanel); // Adding the subpanel to the panelContainer //Report the progress bgWorker.ReportProgress(0, i); // Reporting number of panels loaded } e.Result = imagePanel; // Send the result(a panel with lots of subpanels) as an argument } private void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e) { this.progressBar.Value = (int)e.UserState; this.progressBar.Update(); } private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { if (e.Error == null) { this.panelHolder = (Panel)e.Result; } else { MessageBox.Show("An error occured, please try again"); } } } Instansiating an object of this class: public partial class Draw: Form { public Draw() { ProgressBar progressBarLoading = new ProgressBar(); // Set lots of properties on progressBarLoading Panel panelBigPanelContainer = new Panel(); Drawing drawer = new Drawing(ref progressBarLoading, ref panelBigPanelContainer); drawer.createDrawing(); // this makes the object start a new thread, loading all the panels into a panel container, while also sending the progress to this progressbar. } } Here is my problem: In the private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) i don't get the e.Result as it should be. When i debug and look at the e.Result, the panel's properties have this exception message: '((System.Windows.Forms.Control)(e.Result)).ClientSize' threw an exception of type 'System.ObjectDisposedException' So the object gets disposed, but "why" is my question, and how can i fix this? I hope someone will answer me, this is making me crazy. Another question i have: Is it allowed to use "ref" with arguments? is it bad programming? Thanks in advance. I have also written how i understand the Background worker below here: This is what i think is the "rules" for background workers: bgWorker.RunWorkerAsync(); => starts a new thread. bgWorker_DoWork cannot reach the main thread without delegates - private void bgWorker_DoWork(object sender, DoWorkEventArgs e) { // The work happens here, this is a thread that is not reachable by the main thread e.Result => This is an argument which can be reached by bgWorker_RunWorkerCompleted() bgWorker.ReportProgress(progressVar); => Reports the progress to the bgWorker_ProgressChanged() } - private void bgWorker_ProgressChanged(object sender, ProgressChangedEventArgs e) { // I get the progress here, and can do stuff to the main thread from here (e.g update a control) this.ProgressBar.Value = e.ProgressPercentage; } - private void bgWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e) { // This is where the thread is completed. // Here i can get e.Result from the bgWorker thread // From here i can reach controls in my main thread, and use e.Result in my main thread if (e.Error == null) { this.panelTileHolder = (Panel)e.Result; } else { MessageBox.Show("There was an error"); } }

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• iPhone Crash Report

  - by skywalker168

  My iPhone app is crashing for certain users in UK. I tried using UK timezone and their region format but couldn't reproduce the crash on my iPhone or emulator. Eventually got a crash report and I was able to symbolicate it. However, I have a hard time understanding the results. It appears thread 0 crashed in a system library. The only call from my app is main.m. Thread 4 has something familiar. It was at: My App 0x00004cca -[TocTableController parser:didEndElement:namespaceURI:qualifiedName:] (TocTableController.m:1369) Code is: NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease]; It crashed doing alloc/init? Out of memory, only in UK? Any one has idea what might be cause? Thanks in advance! Date/Time: 2010-04-06 21:41:17.629 +0100 OS Version: iPhone OS 3.1.3 (7E18) Report Version: 104 Exception Type: EXC_CRASH (SIGABRT) Exception Codes: 0x00000000, 0x00000000 Crashed Thread: 0 Thread 0 Crashed: 0 libSystem.B.dylib 0x00090b2c __kill + 8 1 libSystem.B.dylib 0x00090b1a kill + 4 2 libSystem.B.dylib 0x00090b0e raise + 10 3 libSystem.B.dylib 0x000a7e34 abort + 36 4 libstdc++.6.dylib 0x00066390 __gnu_cxx::__verbose_terminate_handler() + 588 5 libobjc.A.dylib 0x00008898 _objc_terminate + 160 6 libstdc++.6.dylib 0x00063a84 __cxxabiv1::__terminate(void (*)()) + 76 7 libstdc++.6.dylib 0x00063afc std::terminate() + 16 8 libstdc++.6.dylib 0x00063c24 __cxa_throw + 100 9 libobjc.A.dylib 0x00006e54 objc_exception_throw + 104 10 Foundation 0x0000202a __NSThreadPerformPerform + 574 11 CoreFoundation 0x000573a0 CFRunLoopRunSpecific + 1908 12 CoreFoundation 0x00056c18 CFRunLoopRunInMode + 44 13 GraphicsServices 0x000041c0 GSEventRunModal + 188 14 UIKit 0x00003c28 -[UIApplication _run] + 552 15 UIKit 0x00002228 UIApplicationMain + 960 16 My App 0x00002414 main (main.m:14) 17 My App 0x000023e4 start + 32 Thread 1: 0 libSystem.B.dylib 0x00001488 mach_msg_trap + 20 1 libSystem.B.dylib 0x00004064 mach_msg + 60 2 CoreFoundation 0x00057002 CFRunLoopRunSpecific + 982 3 CoreFoundation 0x00056c18 CFRunLoopRunInMode + 44 4 WebCore 0x000841d4 RunWebThread(void*) + 412 5 libSystem.B.dylib 0x0002b780 _pthread_body + 20 Thread 2: 0 libSystem.B.dylib 0x00001488 mach_msg_trap + 20 1 libSystem.B.dylib 0x00004064 mach_msg + 60 2 CoreFoundation 0x00057002 CFRunLoopRunSpecific + 982 3 CoreFoundation 0x00056c18 CFRunLoopRunInMode + 44 4 Foundation 0x0005a998 +[NSURLConnection(NSURLConnectionReallyInternal) _resourceLoadLoop:] + 172 5 Foundation 0x00053ac6 -[NSThread main] + 42 6 Foundation 0x00001d0e __NSThread__main__ + 852 7 libSystem.B.dylib 0x0002b780 _pthread_body + 20 Thread 3: 0 libSystem.B.dylib 0x000262c0 select$DARWIN_EXTSN + 20 1 CoreFoundation 0x000207e2 __CFSocketManager + 342 2 libSystem.B.dylib 0x0002b780 _pthread_body + 20 Thread 4: 0 libSystem.B.dylib 0x00015764 fegetenv + 0 1 libSystem.B.dylib 0x0002a160 time + 8 2 libicucore.A.dylib 0x00009280 uprv_getUTCtime + 6 3 libicucore.A.dylib 0x0000a492 icu::Calendar::getNow() + 2 4 libicucore.A.dylib 0x0000a2a0 icu::GregorianCalendar::GregorianCalendar(icu::Locale const&, UErrorCode&) + 86 5 libicucore.A.dylib 0x0000a242 icu::GregorianCalendar::GregorianCalendar(icu::Locale const&, UErrorCode&) + 2 6 libicucore.A.dylib 0x000098ec icu::Calendar::createInstance(icu::TimeZone*, icu::Locale const&, UErrorCode&) + 160 7 libicucore.A.dylib 0x00008762 icu::SimpleDateFormat::initializeCalendar(icu::TimeZone*, icu::Locale const&, UErrorCode&) + 28 8 libicucore.A.dylib 0x0000bd2c icu::SimpleDateFormat::SimpleDateFormat(icu::Locale const&, UErrorCode&) + 82 9 libicucore.A.dylib 0x0000bcd2 icu::SimpleDateFormat::SimpleDateFormat(icu::Locale const&, UErrorCode&) + 2 10 libicucore.A.dylib 0x000084aa icu::DateFormat::create(icu::DateFormat::EStyle, icu::DateFormat::EStyle, icu::Locale const&) + 148 11 libicucore.A.dylib 0x0000840e icu::DateFormat::createDateTimeInstance(icu::DateFormat::EStyle, icu::DateFormat::EStyle, icu::Locale const&) + 14 12 libicucore.A.dylib 0x00008336 udat_open + 70 13 CoreFoundation 0x0006c2e0 CFDateFormatterCreate + 252 14 Foundation 0x00019fd2 -[NSDateFormatter _regenerateFormatter] + 198 15 Foundation 0x00019ebe -[NSDateFormatter init] + 150 16 My App 0x00004cca -[TocTableController parser:didEndElement:namespaceURI:qualifiedName:] (TocTableController.m:1369) 17 Foundation 0x000380e6 _endElementNs + 442 18 libxml2.2.dylib 0x00011d2c xmlParseXMLDecl + 1808 19 libxml2.2.dylib 0x0001ef08 xmlParseChunk + 3300 20 Foundation 0x0003772a -[NSXMLParser parse] + 178 21 My App 0x000055e2 -[TocTableController parseTocData:] (TocTableController.m:1120) 22 Foundation 0x00053ac6 -[NSThread main] + 42 23 Foundation 0x00001d0e __NSThread__main__ + 852 24 libSystem.B.dylib 0x0002b780 _pthread_body + 20 Thread 0 crashed with ARM Thread State: r0: 0x00000000 r1: 0x00000000 r2: 0x00000001 r3: 0x384e83cc r4: 0x00000006 r5: 0x001d813c r6: 0x2ffff2b8 r7: 0x2ffff2c8 r8: 0x38385cac r9: 0x0000000a r10: 0x0002c528 r11: 0x0012be50 ip: 0x00000025 sp: 0x2ffff2c8 lr: 0x33b3db21 pc: 0x33b3db2c cpsr: 0x00070010

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• Matrix Multiplication with Threads: Why is it not faster?

  - by prelic

  Hey all, So I've been playing around with pthreads, specifically trying to calculate the product of two matrices. My code is extremely messy because it was just supposed to be a quick little fun project for myself, but the thread theory I used was very similar to: #include <pthread.h> #include <stdio.h> #include <stdlib.h> #define M 3 #define K 2 #define N 3 #define NUM_THREADS 10 int A [M][K] = { {1,4}, {2,5}, {3,6} }; int B [K][N] = { {8,7,6}, {5,4,3} }; int C [M][N]; struct v { int i; /* row */ int j; /* column */ }; void *runner(void *param); /* the thread */ int main(int argc, char *argv[]) { int i,j, count = 0; for(i = 0; i < M; i++) { for(j = 0; j < N; j++) { //Assign a row and column for each thread struct v *data = (struct v *) malloc(sizeof(struct v)); data->i = i; data->j = j; /* Now create the thread passing it data as a parameter */ pthread_t tid; //Thread ID pthread_attr_t attr; //Set of thread attributes //Get the default attributes pthread_attr_init(&attr); //Create the thread pthread_create(&tid,&attr,runner,data); //Make sure the parent waits for all thread to complete pthread_join(tid, NULL); count++; } } //Print out the resulting matrix for(i = 0; i < M; i++) { for(j = 0; j < N; j++) { printf("%d ", C[i][j]); } printf("\n"); } } //The thread will begin control in this function void *runner(void *param) { struct v *data = param; // the structure that holds our data int n, sum = 0; //the counter and sum //Row multiplied by column for(n = 0; n< K; n++){ sum += A[data->i][n] * B[n][data->j]; } //assign the sum to its coordinate C[data->i][data->j] = sum; //Exit the thread pthread_exit(0); } source: http://macboypro.com/blog/2009/06/29/matrix-multiplication-in-c-using-pthreads-on-linux/ For the non-threaded version, I used the same setup (3 2-d matrices, dynamically allocated structs to hold r/c), and added a timer. First trials indicated that the non-threaded version was faster. My first thought was that the dimensions were too small to notice a difference, and it was taking longer to create the threads. So I upped the dimensions to about 50x50, randomly filled, and ran it, and I'm still not seeing any performance upgrade with the threaded version. What am I missing here?

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• IOException during blocking network NIO in JDK 1.7

  - by Bass

  I'm just learning NIO, and here's the short example I've written to test how a blocking NIO can be interrupted: class TestBlockingNio { private static final boolean INTERRUPT_VIA_THREAD_INTERRUPT = true; /** * Prevent the socket from being GC'ed */ static Socket socket; private static SocketChannel connect(final int port) { while (true) { try { final SocketChannel channel = SocketChannel.open(new InetSocketAddress(port)); channel.configureBlocking(true); return channel; } catch (final IOException ioe) { try { Thread.sleep(1000); } catch (final InterruptedException ie) { } continue; } } } private static byte[] newBuffer(final int length) { final byte buffer[] = new byte[length]; for (int i = 0; i < length; i++) { buffer[i] = (byte) 'A'; } return buffer; } public static void main(final String args[]) throws IOException, InterruptedException { final int portNumber = 10000; new Thread("Reader") { public void run() { try { final ServerSocket serverSocket = new ServerSocket(portNumber); socket = serverSocket.accept(); /* * Fully ignore any input from the socket */ } catch (final IOException ioe) { ioe.printStackTrace(); } } }.start(); final SocketChannel channel = connect(portNumber); final Thread main = Thread.currentThread(); final Thread interruptor = new Thread("Inerruptor") { public void run() { System.out.println("Press Enter to interrupt I/O "); while (true) { try { System.in.read(); } catch (final IOException ioe) { ioe.printStackTrace(); } System.out.println("Interrupting..."); if (INTERRUPT_VIA_THREAD_INTERRUPT) { main.interrupt(); } else { try { channel.close(); } catch (final IOException ioe) { System.out.println(ioe.getMessage()); } } } } }; interruptor.setDaemon(true); interruptor.start(); final ByteBuffer buffer = ByteBuffer.allocate(32768); int i = 0; try { while (true) { buffer.clear(); buffer.put(newBuffer(buffer.capacity())); buffer.flip(); channel.write(buffer); System.out.print('X'); if (++i % 80 == 0) { System.out.println(); Thread.sleep(100); } } } catch (final ClosedByInterruptException cbie) { System.out.println("Closed via Thread.interrupt()"); } catch (final AsynchronousCloseException ace) { System.out.println("Closed via Channel.close()"); } } } In the above example, I'm writing to a SocketChannel, but noone is reading from the other side, so eventually the write operation hangs. This example works great when run by JDK-1.6, with the following output: Press Enter to interrupt I/O XXXX Interrupting... Closed via Thread.interrupt() — meaning that only 128k of data was written to the TCP socket's buffer. When run by JDK-1.7 (1.7.0_25-b15 and 1.7.0-u40-b37), however, the very same code bails out with an IOException: Press Enter to interrupt I/O XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX XXXXXXXXXXX Exception in thread "main" java.io.IOException: Broken pipe at sun.nio.ch.FileDispatcherImpl.write0(Native Method) at sun.nio.ch.SocketDispatcher.write(SocketDispatcher.java:47) at sun.nio.ch.IOUtil.writeFromNativeBuffer(IOUtil.java:93) at sun.nio.ch.IOUtil.write(IOUtil.java:65) at sun.nio.ch.SocketChannelImpl.write(SocketChannelImpl.java:487) at com.example.TestBlockingNio.main(TestBlockingNio.java:109) Can anyone explain this different behaviour?

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• Async networking + threading problem

  - by randallmeadows

  I kick off a network request, assuming no login credentials are required to talk to the destination server. If they are required, then I get an authentication challenge, at which point I display a view requesting said credentials from the user. When they are supplied, I restart the network request, using those credentials. That's all fine and dandy, as long as I only do one request at a time. But I'm not, typically. When both requests are kicked off, I get the first challenge, and present the prompt (using -presentModalViewController:). Then the 2nd challenge comes in. And I crash when it tries to display the 2nd prompt. I have the bulk of this wrapped in an @synchronized() block, but this has no effect because these delegate methods are all being called on the same (main) thread. The docs say the delegate methods are called on the same thread in which the connection was started. OK, no problem; I'll just write a method that I run on a background thread using -performSelectorInBackground: NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO]; [connections addObject:connection]; [self performSelectorInBackground:@selector(startConnection:) withObject:connection]; [connection release]; - (void)startConnection:(NSURLConnection *)connection { NSAutoreleasePool *pool = [NSAutoreleasePool new]; [connection scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode]; [connection start]; [pool drain]; } which should put every network request, and its callbacks, on its own thread, and then my @synchronized() blocks will take effect. The docs for -initWithRequest:... state "Messages to the delegate will be sent on the thread that calls this method. By default, for the connection to work correctly the calling thread’s run loop must be operating in the default run loop mode." Ok, I'm doing that. They also state "If you pass NO [for startImmediately], you must schedule the connection in a run loop before starting it." OK, I'm doing that, too. Furthermore, the docs for NSRunLoop state "Each NSThread object, including the application’s main thread, has an NSRunLoop object automatically created for it as needed. If you need to access the current thread’s run loop, you do so with the class method currentRunLoop." I'm assuming this applies to the background thread created by the call -performSelectorInBackground... (which does appear to be the case, when I execute 'po [NSClassFromString(@"NSRunLoop") currentRunLoop]' in the -startConnection: method). The -startConnection: method is indeed being called. But after kicking off the connection, I now never get any callbacks on it. None of the -connectionDid… delegate methods. (I even tried explicitly starting the thread's run loop, but that made no difference; I've used threads like this before, and I've never had to start the run loop manually before--but I'm now grasping at straws...) I think I've come up with a workaround such that I only handle one request at a time, but it's kludgy and I'd like to do this the Right Way. But, what am I missing here? Thanks! randy

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• iPhone: how to use performSelector:onThread:withObject:waitUntilDone: method?

  - by Michael Kessler

  Hi all, I am trying to use a separate thread for working with some API. The problem is that I am not able to use performSelector:onThread:withObject:waitUntilDone: method with a thread that I' instantiated for this. My code: @interface MyObject : NSObject { NSThread *_myThread; } @property(nonatomic, retain) NSThread *myThread; @end @implementation MyObject @synthesize myThread = _myThread; - (NSThread *)myThread { if (_myThread == nil) { NSThread *myThreadTemp = [[NSThread alloc] init]; [myThreadTemp start]; self. myThread = myThreadTemp; [myThreadTemp release]; } return _myThread; } - (id)init { if (self = [super init]) { [self performSelector:@selector(privateInit:) onThread:[self myThread] withObject:nil waitUntilDone:NO]; } return self; } - (void)privateInit:(id)object { NSLog(@"MyObject - privateInit start"); } - (void)dealloc { [_myThread release]; _myThread = nil; [super dealloc]; } @end "MyObject - privateInit start" is never printed. What am I missing? I tried to instantiate the thread with target and selector, tried to wait for method execution completion (waitUntilDone:YES). Nothing helps. UPDATE: I don't need this multithreading for separating costly operations to another thread. In this case I could use the performSelectorInBackground as mentioned in few answers. The main reason for this separate thread is the need to perform all the actions in the API (TTS by Loquendo) from one single thread. Meaning that I have to create an instance of the TTS object and call methods on that object from the same thread all the time.

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• Logging in worker threads spawned from a pylons application does not seem to work

  - by TimM

  I have a pylons application where, under certain cirumstances I want to spawn multiple worker threads to process items in a queue. Right now we aren't making use of a ThreadPool (would be ideal, but we'll add that in later). The main problem is that the worker threads logging does not get written to the log files. When I run the code outside of the pylons application the logging works fine. So I think its something to do with the pylons log handler but not sure what. Here is a basic example of the code (trimmed down): import logging log = logging.getLogger(__name__) import sys from Queue import Queue from threading import Thread, activeCount def run(input, worker, args = None, simulteneousWorkerLimit = None): queue = Queue() threads = [] if args is not None: if len(args) > 0: args = list(args) args = [worker, queue] + args args = tuple(args) else: args = (worker, queue) # start threads for i in range(4): t = Thread(target = __thread, args = args) t.daemon = True t.start() threads.append(t) # add ThreadTermSignal inputData = list(input) inputData.extend([ThreadTermSignal] * 4) # put in the queue for data in inputData: queue.put(data) # block until all contents are downloaded queue.join() log.critical("** A log line that appears fine **") del queue for thread in threads: del thread del threads class ThreadTermSignal(object): pass def __thread(worker, queue, *args): try: while True: data = queue.get() if data is ThreadTermSignal: sys.exit() try: log.critical("** I don't appear when run under pylons **") finally: queue.task_done() except SystemExit: queue.task_done() pass Take note, that the log lin within the RUN method will show up in the log files, but the log line within the worker method (which is run in a spawned thread), does not appear. Any help would be appreciated. Thanks ** EDIT: I should mention that I tried passing in the "log" variable to the worker thread as well as redefining a new "log" variable within the thread and neither worked. ** EDIT: Adding the configuration used for the pylons application (which comes out of the INI file). So the snippet below is from the INI file. [loggers] keys = root [handlers] keys = wsgierrors [formatters] keys = generic [logger_root] level = WARNING handlers = wsgierrors [handler_console] class = StreamHandler args = (sys.stderr,) level = WARNING formatter = generic [handler_wsgierrors] class = pylons.log.WSGIErrorsHandler args = () level = WARNING format = generic

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• SUA + Visual Studio + pthreads

  - by vasek7

  Hi, I cannot compile this code under SUA: #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <pthread.h> void * thread_function(void *arg) { printf("thread_function started. Arg was %s\n", (char *)arg); // pause for 3 seconds sleep(3); // exit and return a message to another thread // that may be waiting for us to finish pthread_exit ("thread one all done"); } int main() { int res; pthread_t a_thread; void *thread_result; // create a thread that starts to run ‘thread_function’ pthread_create (&a_thread, NULL, thread_function, (void*)"thread one"); printf("Waiting for thread to finish...\n"); // now wait for new thread to finish // and get any returned message in ‘thread_result’ pthread_join(a_thread, &thread_result); printf("Thread joined, it returned %s\n", (char *)thread_result); exit(0); } I'm running on Windows 7 Ultimate x64 with Visual Studio 2008 and 2010 and I have installed: Windows Subsystem for UNIX Utilities and SDK for Subsystem for UNIX-based Applications in Microsoft Windows 7 and Windows Server 2008 R2 Include directories property of Visual Studio project is set to "C:\Windows\SUA\usr\include" What I have to configure in order to compile and run (and possibly debug) pthreads programs in Visual Studio 2010 (or 2008)?

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• Background worker not working right

  - by vbNewbie

  I have created a background worker to go and run a pretty long task that includes creating more threads which will read from a file of urls and crawl each. I tried following it through debugging and found that the background process ends prematurely for no apparent reason. Is there something wrong in the logic of my code that is causing this. I will try and paste as much as possible to make sense. While Not myreader.EndOfData Try currentRow = myreader.ReadFields() Dim currentField As String For Each currentField In currentRow itemCount = itemCount + 1 searchItem = currentField generateSearchFromFile(currentField) processQuerySearch() Next Catch ex As Microsoft.VisualBasic.FileIO.MalformedLineException Console.WriteLine(ex.Message.ToString) End Try End While This first bit of code is the loop to input from file and this is what the background worker does. The next bit of code is where the background worker creates threads to work all the 'landingPages'. After about 10 threads are created the background worker exits this sub and skips the file input loop and exits the program. Try For Each landingPage As String In landingPages pgbar.Timer1.Stop() If VisitedPages.Contains(landingPage) Then Continue For Else Dim thread = New Thread(AddressOf processQuery) count = count + 1 thread.Name = "Worm" & count thread.Start(landingPage) If numThread >= 10 Then For Each thread In ThreadList thread.Join() Next numThread = 0 Continue For Else numThread = numThread + 1 SyncLock ThreadList ThreadList.Add(thread) End SyncLock End If End If Next

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• Servlet requests are executed sequentially for no apparent reason in Glassfish v3

  - by Fabien Benoit

  Hi, I'm using Glassfish 3 Web profile and can't get http workers to execute concurrently requests on a servlet. This is how i observed the problem. I've made a very simple servlet, that writes the current thread name to the standard output and sleep for 10 seconds : protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.out.println(Thread.currentThread().getName()); try { Thread.sleep(10000); // 10 sec } catch (InterruptedException ex) {} } } And when i'm running several simultaneous requests, I clearly see in the logs that the requests are sequentially executed (one trace every 10 seconds). INFO: http-thread-pool-8080-(2) (10 seconds later...) INFO: http-thread-pool-8080-(1) (10 seconds later...) INFO: http-thread-pool-8080-(2) etc. All my GF settings are untouched - it's the out-of-the-box config (the default thread pool is 2 threads min, 5 max if I recall properly). ...I really don't understand why the sleep() block all the others worker threads. Any insight would be greatly appreciated ! Thanks, Fabien

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• Java process is not terminating after starting an external process

  - by tangens

  On Windows I've started a program "async.cmd" with a ProcessBuilder like this: ProcessBuilder processBuilder = new ProcessBuilder( "async.cmd" ); processBuilder.redirectErrorStream( true ); processBuilder.start(); Then I read the output of the process in a separate thread like this: byte[] buffer = new byte[ 8192 ]; while( !interrupted() ) { int available = m_inputStream.available(); if( available == 0 ) { Thread.sleep( 100 ); continue; } int len = Math.min( buffer.length, available ); len = m_inputStream.read( buffer, 0, len ); if( len == -1 ) { throw new CX_InternalError(); } String outString = new String( buffer, 0, len ); m_output.append( outString ); } Now it happened that the content of the file "async.cmd" was this: REM start a command window start cmd /k The process that started this extenal program terminated (process.waitFor() returned the exit value). Then I sent an readerThread.interrupt() to the reader thread and the thread terminated, too. But there was still a thread running that wasn't terminating. This thread kept my java application running even if it exited its main method. With the debugger (eclipse) I wasn't able to suspend this thread. After I quit the opened command window, my java program exited, too. Question How can I quit my java program while the command window stays open?

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• Simple description of worker and I/O threads in .NET

  - by Konstantin

  It's very hard to find detailed but simple description of worker and I/O threads in .NET What's clear to me regarding this topic (but may not be technically precise): Worker threads are threads that should employ CPU for their work; I/O threads (also called "completion port threads") should employ device drivers for their work and essentially "do nothing", only monitor the completion of non-CPU operations. What is not clear: Although method ThreadPool.GetAvailableThreads returns number of available threads of both types, it seems there is no public API to schedule work for I/O thread. You can only manually create worker thread in .NET? It seems that single I/O thread can monitor multiple I/O operations. Is it true? If so, why ThreadPool has so many available I/O threads by default? In some texts I read that callback, triggered after I/O operation completion is performed by I/O thread. Is it true? Isn’t this a job for worker thread, considering that this callback is CPU operation? To be more specific – do ASP.NET asynchronous pages user I/O threads? What exactly is performance benefit in switching I/O work to separate thread instead of increasing maximum number of worker threads? Is it because single I/O thread does monitor multiple operations? Or Windows does more efficient context switching when using I/O threads?

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• How do I print an HTML document from a web service?

  - by Chris Marasti-Georg

  I want to print HTML from a C# web service. The Web Browser control is overkill, and does not function well in a service-environment, nor does it function well on a system with very tight security constraints. Is there any sort of free .NET library that will support the printing of a basic HTML page? Here is the code I have so far, that is not running properly. public void PrintThing(string document) { if (Thread.CurrentThread.GetApartmentState() != ApartmentState.STA) { Thread thread = new Thread((ThreadStart) delegate { PrintDocument(document); }); thread.SetApartmentState(ApartmentState.STA); thread.Start(); } else { PrintDocument(document); } } protected void PrintDocument(string document) { WebBrowser browser = new WebBrowser(); browser.DocumentText = document; while (browser.ReadyState != WebBrowserReadyState.Complete) { Application.DoEvents(); } browser.Print(); } This works fine when called from UI-type threads, but nothing happens when called from a service-type thread. Changing Print() to ShowPrintPreviewDialog() yields the following IE script error: Error: 'dialogArguments.___IE_PrintType' is null or not an object URL: res://ieframe.dll/preview.dlg And a small empty print preview dialog appears.

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• Memory allocation in detached NSThread to load an NSDictionary in background?

  - by mobibob

  I am trying to launch a background thread to retrieve XML data from a web service. I developed it synchronously - without threads, so I know that part works. Now I am ready to have a non-blocking service by spawning a thread to wait for the response and parse. I created an NSAutoreleasePool inside the thread and release it at the end of the parsing. The code to spawn and the thread are as follows: Spawn from main-loop code: . . [NSThread detachNewThreadSelector:@selector(spawnRequestThread:) toTarget:self withObject:url]; . . Thread (inside 'self'): -(void) spawnRequestThread: (NSURL*) url { NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; parser = [[NSXMLParser alloc] initWithContentsOfURL:url]; [self parseContentsOfResponse]; [parser release]; [pool release]; } The method parseContentsOfResponse fills an NSMutableDictionary with the parsed document contents. I would like to avoid moving the data around a lot and allocate it back in the main-loop that spawned the thread rather than making a copy. First, is that possible, and if not, can I simply pass in an allocated pointer from the main thread and allocate with 'dictionaryWithDictionary' method? That just seems so inefficient. Are there perferred designs?

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• BackgroundWorker might be causing my application to hang

  - by alexD

  I have a Form that uses a BackgroundWorker to execute a series of tests. I use the ProgressChanged event to send messages to the main thread, which then does all of the updates on the UI. I've combed through my code to make sure I'm not doing anything to the UI in the background worker. There are no while loops in my code and the BackgroundWorker has a finite execution time (measured in seconds or minutes). However, for some reason when I lock my computer, often times the application will be hung when I log back in. The thing is, the BackgroundWorker isn't even running when this happens. The reason I believe it is related to the BackgroundWorker though is because the form only hangs when the BackgroundWorker has been executed since the application was loaded (it only runs when given a certain user input). I pass this thread a List of TreeNodes from a TreeView in my UI through the RunWorkerAsync method, but I only read those nodes in the worker thread..any modifications I make to them is done in the UI thread through the progressChanged event. I do use Thread.Sleep in my worker thread to execute tests at timed intervals (which involves sending messages over a TCP socket, which was not created in the worker thread). I am completely perplexed as to why my application might be hanging. I'm sure I'm doing something 'illegal' somewhere, I just don't know what.

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• Threading is slow and unpredictable?

  - by Jake

  I've created the basis of a ray tracer, here's my testing function for drawing the scene: public void Trace(int start, int jump, Sphere testSphere) { for (int x = start; x < scene.SceneWidth; x += jump) { for (int y = 0; y < scene.SceneHeight; y++) { Ray fired = Ray.FireThroughPixel(scene, x, y); if (testSphere.Intersects(fired)) sceneRenderer.SetPixel(x, y, Color.Red); else sceneRenderer.SetPixel(x, y, Color.Black); } } } SetPixel simply sets a value in a single dimensional array of colours. If I call the function normally by just directly calling it it runs at a constant 55fps. If I do: Thread t1 = new Thread(() => Trace(0, 1, testSphere)); t1.Start(); t1.Join(); It runs at a constant 50fps which is fine and understandable, but when I do: Thread t1 = new Thread(() => Trace(0, 2, testSphere)); Thread t2 = new Thread(() => Trace(1, 2, testSphere)); t1.Start(); t2.Start(); t1.Join(); t2.Join(); It runs all over the place, rapidly moving between 30-40 fps and sometimes going out of that range up to 50 or down to 20, it's not constant at all. Why is it running slower than it would if I ran the whole thing on a single thread? I'm running on a quad core i5 2500k.

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• Tricky MySQL Query for messaging system in Rails - Please Help

  - by ole_berlin

  Hi, I'm writing a facebook style messaging system for a Rails App and I'm having trouble selecting the Messages for the inbox (with will_paginate). The messages are organized in threads, in the inbox the most recent message of a thread will appear with a link to it's thread. The thread is organized via a parent_id 1-n relationship with itself. So far I'm using something like this: class Message < ActiveRecord::Base belongs_to :sender, :class_name => 'User', :foreign_key => "sender_id" belongs_to :recipient, :class_name => 'User', :foreign_key => "recipient_id" has_many :children, :class_name => "Message", :foreign_key => "parent_id" belongs_to :thread, :class_name => "Message", :foreign_key => "parent_id" end class MessagesController < ApplicationController def inbox @messages = current_user.received_messages.paginate :page => params[:page], :per_page => 10, :order => "created_at DESC" end end That gives me all the messages, but for one thread the thread itself and the most recent message will appear (and not only the most recent message). I can also not use the GROUP BY clause, because for the thread itself (the parent so to say) the parent_id = nil of course. Anyone got an idea on how to solve this in an elegant way? I already thought about adding the parent_id to the parent itself and then group by parent_id, but I'm not sure if that works. Thanks

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• Wait on multiple condition variables on Linux without unnecessary sleeps?

  - by Joseph Garvin

  I'm writing a latency sensitive app that in effect wants to wait on multiple condition variables at once. I've read before of several ways to get this functionality on Linux (apparently this is builtin on Windows), but none of them seem suitable for my app. The methods I know of are: Have one thread wait on each of the condition variables you want to wait on, which when woken will signal a single condition variable which you wait on instead. Cycling through multiple condition variables with a timed wait. Writing dummy bytes to files or pipes instead, and polling on those. #1 & #2 are unsuitable because they cause unnecessary sleeping. With #1, you have to wait for the dummy thread to wake up, then signal the real thread, then for the real thread to wake up, instead of the real thread just waking up to begin with -- the extra scheduler quantum spent on this actually matters for my app, and I'd prefer not to have to use a full fledged RTOS. #2 is even worse, you potentially spend N * timeout time asleep, or your timeout will be 0 in which case you never sleep (endlessly burning CPU and starving other threads is also bad). For #3, pipes are problematic because if the thread being 'signaled' is busy or even crashes (I'm in fact dealing with separate process rather than threads -- the mutexes and conditions would be stored in shared memory), then the writing thread will be stuck because the pipe's buffer will be full, as will any other clients. Files are problematic because you'd be growing it endlessly the longer the app ran. Is there a better way to do this? Curious for answers appropriate for Solaris as well.

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