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• .NET 4 SpinLock

  - by Jon Harrop

  The following test code (F#) is not returning the result I'd expect: let safeCount() = let n = 1000000 let counter = ref 0 let spinlock = ref <| SpinLock(false) let run i0 i1 () = for i=i0 to i1-1 do let locked = ref false try (!spinlock).Enter locked if !locked then counter := !counter + 1 finally if !locked then (!spinlock).Exit() let thread = System.Threading.Thread(run 0 (n/2)) thread.Start() run (n/2) n () thread.Join() !counter I'd expect the SpinLock to mutually exclude the counter and, therefore, for it to return counts of 1,000,000 but, instead, it returns smaller values as if no mutual exclusion is occurring. Any ideas what's wrong?

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• How to marshall COM object on the server side in visual c++?

  - by dos

  I have a out-of-process COM server with an ATL Simple Object which creates another thread. The new thread will need to make calls to ATL Simple object. Since ATL Simple Object and new thread are created different apartments, ATL Simple Object needs to be marshalled in the new thread, otherwise error 0x8001010e will be generated. How do I marshall COM Object on the server side or Am I missing something? Many thanks.

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• What is the fastest cyclic synchronization in Java (ExecutorService vs. CyclicBarrier vs. X)?

  - by Alex Dunlop

  Which Java synchronization construct is likely to provide the best performance for a concurrent, iterative processing scenario with a fixed number of threads like the one outlined below? After experimenting on my own for a while (using ExecutorService and CyclicBarrier) and being somewhat surprised by the results, I would be grateful for some expert advice and maybe some new ideas. Existing questions here do not seem to focus primarily on performance, hence this new one. Thanks in advance! The core of the app is a simple iterative data processing algorithm, parallelized to the spread the computational load across 8 cores on a Mac Pro, running OS X 10.6 and Java 1.6.0_07. The data to be processed is split into 8 blocks and each block is fed to a Runnable to be executed by one of a fixed number of threads. Parallelizing the algorithm was fairly straightforward, and it functionally works as desired, but its performance is not yet what I think it could be. The app seems to spend a lot of time in system calls synchronizing, so after some profiling I wonder whether I selected the most appropriate synchronization mechanism(s). A key requirement of the algorithm is that it needs to proceed in stages, so the threads need to sync up at the end of each stage. The main thread prepares the work (very low overhead), passes it to the threads, lets them work on it, then proceeds when all threads are done, rearranges the work (again very low overhead) and repeats the cycle. The machine is dedicated to this task, Garbage Collection is minimized by using per-thread pools of pre-allocated items, and the number of threads can be fixed (no incoming requests or the like, just one thread per CPU core). V1 - ExecutorService My first implementation used an ExecutorService with 8 worker threads. The program creates 8 tasks holding the work and then lets them work on it, roughly like this: // create one thread per CPU executorService = Executors.newFixedThreadPool( 8 ); ... // now process data in cycles while( ...) { // package data into 8 work items ... // create one Callable task per work item ... // submit the Callables to the worker threads executorService.invokeAll( taskList ); } This works well functionally (it does what it should), and for very large work items indeed all 8 CPUs become highly loaded, as much as the processing algorithm would be expected to allow (some work items will finish faster than others, then idle). However, as the work items become smaller (and this is not really under the program's control), the user CPU load shrinks dramatically: blocksize | system | user | cycles/sec 256k 1.8% 85% 1.30 64k 2.5% 77% 5.6 16k 4% 64% 22.5 4096 8% 56% 86 1024 13% 38% 227 256 17% 19% 420 64 19% 17% 948 16 19% 13% 1626 Legend: - block size = size of the work item (= computational steps) - system = system load, as shown in OS X Activity Monitor (red bar) - user = user load, as shown in OS X Activity Monitor (green bar) - cycles/sec = iterations through the main while loop, more is better The primary area of concern here is the high percentage of time spent in the system, which appears to be driven by thread synchronization calls. As expected, for smaller work items, ExecutorService.invokeAll() will require relatively more effort to sync up the threads versus the amount of work being performed in each thread. But since ExecutorService is more generic than it would need to be for this use case (it can queue tasks for threads if there are more tasks than cores), I though maybe there would be a leaner synchronization construct. V2 - CyclicBarrier The next implementation used a CyclicBarrier to sync up the threads before receiving work and after completing it, roughly as follows: main() { // create the barrier barrier = new CyclicBarrier( 8 + 1 ); // create Runable for thread, tell it about the barrier Runnable task = new WorkerThreadRunnable( barrier ); // start the threads for( int i = 0; i < 8; i++ ) { // create one thread per core new Thread( task ).start(); } while( ... ) { // tell threads about the work ... // N threads + this will call await(), then system proceeds barrier.await(); // ... now worker threads work on the work... // wait for worker threads to finish barrier.await(); } } class WorkerThreadRunnable implements Runnable { CyclicBarrier barrier; WorkerThreadRunnable( CyclicBarrier barrier ) { this.barrier = barrier; } public void run() { while( true ) { // wait for work barrier.await(); // do the work ... // wait for everyone else to finish barrier.await(); } } } Again, this works well functionally (it does what it should), and for very large work items indeed all 8 CPUs become highly loaded, as before. However, as the work items become smaller, the load still shrinks dramatically: blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.7% 78% 6.1 16k 5.5% 52% 25 4096 9% 29% 64 1024 11% 15% 117 256 12% 8% 169 64 12% 6.5% 285 16 12% 6% 377 For large work items, synchronization is negligible and the performance is identical to V1. But unexpectedly, the results of the (highly specialized) CyclicBarrier seem MUCH WORSE than those for the (generic) ExecutorService: throughput (cycles/sec) is only about 1/4th of V1. A preliminary conclusion would be that even though this seems to be the advertised ideal use case for CyclicBarrier, it performs much worse than the generic ExecutorService. V3 - Wait/Notify + CyclicBarrier It seemed worth a try to replace the first cyclic barrier await() with a simple wait/notify mechanism: main() { // create the barrier // create Runable for thread, tell it about the barrier // start the threads while( ... ) { // tell threads about the work // for each: workerThreadRunnable.setWorkItem( ... ); // ... now worker threads work on the work... // wait for worker threads to finish barrier.await(); } } class WorkerThreadRunnable implements Runnable { CyclicBarrier barrier; @NotNull volatile private Callable<Integer> workItem; WorkerThreadRunnable( CyclicBarrier barrier ) { this.barrier = barrier; this.workItem = NO_WORK; } final protected void setWorkItem( @NotNull final Callable<Integer> callable ) { synchronized( this ) { workItem = callable; notify(); } } public void run() { while( true ) { // wait for work while( true ) { synchronized( this ) { if( workItem != NO_WORK ) break; try { wait(); } catch( InterruptedException e ) { e.printStackTrace(); } } } // do the work ... // wait for everyone else to finish barrier.await(); } } } Again, this works well functionally (it does what it should). blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.4% 80% 6.3 16k 4.6% 60% 30.1 4096 8.6% 41% 98.5 1024 12% 23% 202 256 14% 11.6% 299 64 14% 10.0% 518 16 14.8% 8.7% 679 The throughput for small work items is still much worse than that of the ExecutorService, but about 2x that of the CyclicBarrier. Eliminating one CyclicBarrier eliminates half of the gap. V4 - Busy wait instead of wait/notify Since this app is the primary one running on the system and the cores idle anyway if they're not busy with a work item, why not try a busy wait for work items in each thread, even if that spins the CPU needlessly. The worker thread code changes as follows: class WorkerThreadRunnable implements Runnable { // as before final protected void setWorkItem( @NotNull final Callable<Integer> callable ) { workItem = callable; } public void run() { while( true ) { // busy-wait for work while( true ) { if( workItem != NO_WORK ) break; } // do the work ... // wait for everyone else to finish barrier.await(); } } } Also works well functionally (it does what it should). blocksize | system | user | cycles/sec 256k 1.9% 85% 1.30 64k 2.2% 81% 6.3 16k 4.2% 62% 33 4096 7.5% 40% 107 1024 10.4% 23% 210 256 12.0% 12.0% 310 64 11.9% 10.2% 550 16 12.2% 8.6% 741 For small work items, this increases throughput by a further 10% over the CyclicBarrier + wait/notify variant, which is not insignificant. But it is still much lower-throughput than V1 with the ExecutorService. V5 - ? So what is the best synchronization mechanism for such a (presumably not uncommon) problem? I am weary of writing my own sync mechanism to completely replace ExecutorService (assuming that it is too generic and there has to be something that can still be taken out to make it more efficient). It is not my area of expertise and I'm concerned that I'd spend a lot of time debugging it (since I'm not even sure my wait/notify and busy wait variants are correct) for uncertain gain. Any advice would be greatly appreciated.

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• algorithm for python itertools.permutations

  - by zaharpopov

  Can someone please explain algorithm for itertools.permutations routine in Python standard lib 2.6? I see its code in the documentation but don't undestand why it work? Thanks Code is: def permutations(iterable, r=None): # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC # permutations(range(3)) --> 012 021 102 120 201 210 pool = tuple(iterable) n = len(pool) r = n if r is None else r if r > n: return indices = range(n) cycles = range(n, n-r, -1) yield tuple(pool[i] for i in indices[:r]) while n: for i in reversed(range(r)): cycles[i] -= 1 if cycles[i] == 0: indices[i:] = indices[i+1:] + indices[i:i+1] cycles[i] = n - i else: j = cycles[i] indices[i], indices[-j] = indices[-j], indices[i] yield tuple(pool[i] for i in indices[:r]) break else: return

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• Benefit of using multiple SIMD instruction sets simultaneously

  - by GenTiradentes

  I'm writing a highly parallel application that's multithreaded. I've already got an SSE accelerated thread class written. If I were to write an MMX accelerated thread class, then run both at the same time (one SSE thread and one MMX thread per core) would the performance improve noticeably? I would think that this setup would help hide memory latency, but I'd like to be sure before I start pouring time into it.

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• Implementing Unit Testing with the iPhone SDK

  - by ing0

  Hi, So I've followed this tutorial to setup unit testing on my app when I got a little stuck. At bullet point 8 in that tutorial it shows this image, which is what I should be expecting when I build: However this isn't what I get when I build. I get this error message: Command /bin/sh failed with exit code 1 as well as the error message the unit test has created. Then, when I expand on the first error I get this: PhaseScriptExecution "Run Script" "build/3D Pool.build/Debug-iphonesimulator/LogicTests.build/Script-1A6BA6AE10F28F40008AC2A8.sh" cd "/Users/james/Desktop/FYP/3D Pool" setenv ACTION build setenv ALTERNATE_GROUP staff ... setenv XCODE_VERSION_MAJOR 0300 setenv XCODE_VERSION_MINOR 0320 setenv YACC /Developer/usr/bin/yacc /bin/sh -c "\"/Users/james/Desktop/FYP/3D Pool/build/3D Pool.build/Debug-iphonesimulator/LogicTests.build/Script-1A6BA6AE10F28F40008AC2A8.sh\"" /Developer/Tools/RunPlatformUnitTests.include:412: note: Started tests for architectures 'i386' /Developer/Tools/RunPlatformUnitTests.include:419: note: Running tests for architecture 'i386' (GC OFF) objc[12589]: GC: forcing GC OFF because OBJC_DISABLE_GC is set Test Suite '/Users/james/Desktop/FYP/3D Pool/build/Debug-iphonesimulator/LogicTests.octest(Tests)' started at 2010-01-04 21:05:06 +0000 Test Suite 'LogicTests' started at 2010-01-04 21:05:06 +0000 Test Case '-[LogicTests testFail]' started. /Users/james/Desktop/FYP/3D Pool/LogicTests.m:17: error: -[LogicTests testFail] : Must fail to succeed. Test Case '-[LogicTests testFail]' failed (0.000 seconds). Test Suite 'LogicTests' finished at 2010-01-04 21:05:06 +0000. Executed 1 test, with 1 failure (0 unexpected) in 0.000 (0.000) seconds Test Suite '/Users/james/Desktop/FYP/3D Pool/build/Debug-iphonesimulator/LogicTests.octest(Tests)' finished at 2010-01-04 21:05:06 +0000. Executed 1 test, with 1 failure (0 unexpected) in 0.000 (0.002) seconds /Developer/Tools/RunPlatformUnitTests.include:448: error: Failed tests for architecture 'i386' (GC OFF) /Developer/Tools/RunPlatformUnitTests.include:462: note: Completed tests for architectures 'i386' Command /bin/sh failed with exit code 1 Now this is very odd as it is running the tests (and succeeding as you can see my STFail firing) because if I add a different test which passes I get no errors, so the tests are working fine. But why am I getting this extra build fail? It may also be of note that when downloading solutions/templates which should work out the box, I get the same error. I'm guessing I've set something up wrong here but I've just followed a tutorial 100% correctly!! If anyone could help I'd be very grateful! Thanks EDIT: According to this blog, this post and a few other websites, I'm not the only one getting this problem. It has been like this since the release of xCode 3.2, assuming the apple dev center documents and tutorials etc are pre-3.2 as well. However some say its a known issue whereas others seem to think this was intentional. I for one would like both the extended console and in code messages, and I certainly do not like the "Command /bin/sh..." error and really think they would have documented such an update. Hopefully it will be fixed soon anyway. UPDATE: Here's confirmation it's something changed since the release of xCode 3.2.1. This image: is from my test build using 3.2.1. This one is from an older version (3.1.4): . (The project for both was unchanged). Edit: Image URLS updated.

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• Django - Threading in views without hanging the server

  - by bobthabuilda

  One of my applications in my Django project require each request/visitor to that instance to have their own thread. This might sound confusing, so I'll describe what I'm looking to accomplish in a case based scenario, with steps: User visits application Thread starts Until the thread finishes, that user's server instance hangs Once the thread completes, a response is delivered to the user Other visitors to the site should not be affected by any other users using the application How can I accomplish something like this? If possible, I'd like to find a lightweight solution.

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• WPF Dispatcher.BeginInvoke crash on Windows XP

  - by amr-ne

  Hi, I have a WPF application and a worker thread. The worker thread invokes a callback on the UI thread, which opens a new dialog. Works fine on Win7, but on XP it will crash. In worker thread: someWpfDialogInstance.Dispatcher.BeginInvoke(openSomeDialogCallback, null); Does someone knows a solution or a workaround for this problem?

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• How can Swing dialogs even work?

  - by Bart van Heukelom

  If you open a dialog in Swing, for example a JFileChooser, it goes somewhat like this pseudocode: swing event thread { create dialog add listener to dialog close event { returnValue = somethingFromDialog } show dialog (wait until it is closed) return returnValue } My question is: how can this possibly work? As you can see the thread waits to return until the dialog is closed. This means the Swing event thread is blocked. Yet, one can interact with the dialog, which AFAIK requires this thread to run. So how does that work?

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• C# threading question

  - by MusiGenesis

  Is there any essential difference between this code: ThreadStart starter = new ThreadStart(SomeMethod); starter.Invoke(); and this? ThreadStart starter = new ThreadStart(SomeMethod); Thread th = new Thread(starter); th.Start(); Or does the first invoke the method on the current thread while the second invokes it on a new thread?

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• junit annotation

  - by lamisse

  I wish to launch the GUI appli 2 times from java test how should we use @annotation in this case? example : @BeforeClass public static void setupOnce() { final Thread thread = new Thread() { public void run() { //launche appli } }; try { thread.start(); when I call this function from test @test public void test(){ setuponce(); } to launch it a second time which annotation should I use? @afterclass? thanks

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• .NET threading question

  - by MusiGenesis

  Is there any essential difference between this code: ThreadStart starter = new ThreadStart(SomeMethod); starter.Invoke(); and this? ThreadStart starter = new ThreadStart(SomeMethod); Thread th = new Thread(starter); th.Start(); Or does the first invoke the method on the current thread while the second invokes it on a new thread?

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• How to set up single array or dictionary for use in multiple datasources?

  - by Roman

  I have multiple TableViewDatasources that need to display list of objects form same pool depending of certain property. E.g. object.flag1 is set- it will show up in TableView1 object.flag2 is set- it will show up in TableView2 The obvious way would be to have separate arrays for each TableView, But same object may appear in different arrays. Also I need to update objects very often or access all objects through same array. How do I setup a single dictionary or array to have all objects in one structure? To put it in another way: When table view or selection changes, application need to redraw TableViews with the new data. Application have to access the pool of objects and search through them using iterator and accessing each object and its properties. I think that this is an expensive operation and want to avoid that. Perhaps maybe by making a global pool of objects a dictionary and exposing objects properties as dictionary fields. So instead of iterating global pool of objects I could access global pool Dicitonary in a manner of database by selecting objects that has fields that match particular criteria. Anyone know any example of doing that?

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• Understanding Java Wait and Notify methods

  - by Maddy

  Hello all: I have a following program: import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; public class SimpleWaitNotify implements Runnable { final static Object obj = new Object(); static boolean value = true; public synchronized void flag() { System.out.println("Before Wait"); try { obj.wait(); } catch (InterruptedException e) { System.out.println("Thread interrupted"); } System.out.println("After Being Notified"); } public synchronized void unflag() { System.out.println("Before Notify All"); obj.notifyAll(); System.out.println("After Notify All Method Call"); } public void run() { if (value) { flag(); } else { unflag(); } } public static void main(String[] args) throws InterruptedException { ExecutorService pool = Executors.newFixedThreadPool(4); SimpleWaitNotify sWait = new SimpleWaitNotify(); pool.execute(sWait); SimpleWaitNotify.value = false; SimpleWaitNotify sNotify = new SimpleWaitNotify(); pool.execute(sNotify); pool.shutdown(); } } When I wait on obj, I get the following exception Exception in thread "pool-1-thread-1" java.lang.IllegalMonitorStateException: current thread not owner for each of the two threads. But if I use SimpleWaitNotify's monitor then the program execution is suspended. In other words, I think it suspends current execution thread and in turn the executor. Any help towards understanding what's going on would be duly appreciated. This is an area1 where the theory and javadoc seem straightforward, and since there aren't many examples, conceptually left a big gap in me.

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• iPhone App is leaking memory; Instruments and Clang cannot find the leak

  - by Norbert

  Hi, i've developed an iPhone program which is kind of an image manipulation program: The user get an UIImagePickerController and selects an image. Then the program does some heavy calculating in a new thread (for responsiveness of the application). The thread has, of course, its own autorelease pool. When calculation is done, the seperated thread signals the main thread that the result can be presented. The app creates a new view controller, pushes it onto the navigation controller. In short: UIImagePickerController new thread (autorelease pool) does some heavy calculation with image data signal to main thread that it's done main thread creates view controller and pushes it onto navigation controller view controller presents image result My program works well, but if I dismiss the navigation controller's top view controller by tapping on the back button and repeat the whole process several times, my app crashes. But only on the device! Instruments cannot find any leaks (except for some minor ones which I don't feel responsible for: thread creation, NSCFString; overall about 10 kB). Even Clang static analyzer tells me that my could seems to be all right. I know that the UIImage class can cache images and objects returned from convenience methods get freed only whet their autorelease pool gets drained. But most of the time I work with CGImageRef and I use UIImage' alloc, init & release methods to free memory as soon as possible. Currently, I don't know how to isolate the problem. How would you approach this problem? Crash Log: Incident Identifier: F4C202C9-1338-48FC-80AD-46248E6C7154 CrashReporter Key: bb6f526d8b9bb680f25ea8e93bb071566ccf1776 OS Version: iPhone OS 3.1.1 (7C145) Date: 2009-09-26 14:18:57 +0200 Free pages: 372 Wired pages: 7754 Purgeable pages: 0 Largest process: _MY_APP_ Processes Name UUID Count resident pages _MY_APP_ <032690e5a9b396058418d183480a9ab3> 17766 (jettisoned) (active) debugserver <ec29691560aa0e2994f82f822181bffd> 107 syslog_relay <21e13fa2b777218bdb93982e23fb65d3> 62 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 afcd <98b45027fbb1350977bf1ca313dee527> 65 mediaserverd <eb8fe997a752407bea573cd3adf568d3> 319 ptpd <b17af9cf6c4ad16a557d6377378e8a1e> 142 syslogd <ec8a5bc4483638539fa1266363dee8b8> 68 BTServer <1bb74831f93b1d07c48fb46cc31c15da> 119 apsd <a639ba83e666cc1d539223923ce59581> 165 notifyd <2ed3a1166da84d8d8868e64d549cae9d> 101 CommCenter <f4239480a623fb1c35fa6c725f75b166> 161 SpringBoard <8919df8091fdfab94d9ae05f513c0ce5> 2681 (active) accessoryd <b66bcf6e77c3ee740c6a017f54226200> 90 configd <41e9d763e71dc0eda19b0afec1daee1d> 275 fairplayd <cdce5393153c3d69d23c05de1d492bd4> 108 mDNSResponder <f3ef7a6b24d4f203ed147f476385ec53> 103 lockdownd <6543492543ad16ff0707a46e512944ff> 297 launchd <73ce695fee09fc37dd70b1378af1c818> 71 **End**

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• How to do the processing and keep GUI refreshed using databinding?

  - by macias

  History of the problem This is continuation of my previous question How to start a thread to keep GUI refreshed? but since Jon shed new light on the problem, I would have to completely rewrite original question, which would make that topic unreadable. So, new, very specific question. The problem Two pieces: CPU hungry heavy-weight processing as a library (back-end) WPF GUI with databinding which serves as monitor for the processing (front-end) Current situation -- library sends so many notifications about data changes that despite it works within its own thread it completely jams WPF data binding mechanism, and in result not only monitoring the data does not work (it is not refreshed) but entire GUI is frozen while processing the data. The aim -- well-designed, polished way to keep GUI up to date -- I am not saying it should display the data immediately (it can skip some changes even), but it cannot freeze while doing computation. Example This is simplified example, but it shows the problem. XAML part: <StackPanel Orientation="Vertical"> <Button Click="Button_Click">Start</Button> <TextBlock Text="{Binding Path=Counter}"/> </StackPanel> C# part (please NOTE this is one piece code, but there are two sections of it): public partial class MainWindow : Window,INotifyPropertyChanged { // GUI part public MainWindow() { InitializeComponent(); DataContext = this; } private void Button_Click(object sender, RoutedEventArgs e) { var thread = new Thread(doProcessing); thread.IsBackground = true; thread.Start(); } // this is non-GUI part -- do not mess with GUI here public event PropertyChangedEventHandler PropertyChanged; public void OnPropertyChanged(string property_name) { if (PropertyChanged != null) PropertyChanged(this, new PropertyChangedEventArgs(property_name)); } long counter; public long Counter { get { return counter; } set { if (counter != value) { counter = value; OnPropertyChanged("Counter"); } } } void doProcessing() { var tmp = 10000.0; for (Counter = 0; Counter < 10000000; ++Counter) { if (Counter % 2 == 0) tmp = Math.Sqrt(tmp); else tmp = Math.Pow(tmp, 2.0); } } } Known workarounds (Please do not repost them as answers) Those two first are based on Jon ideas: pass GUI dispatcher to library and use it for sending notifications -- why it is ugly? because it could be no GUI at all give up with data binding COMPLETELY (one widget with databinding is enough for jamming), and instead check from time to time data and update the GUI manually -- well, I didn't learn WPF just to give up with it now ;-) and this is mine, it is ugly, but simplicity of it kills -- before sending notification freeze a thread -- Thread.Sleep(1) -- to let the potential receiver "breathe" -- it works, it is minimalistic, it is ugly though, and it ALWAYS slows down computation even if no GUI is there So... I am all ears for real solutions, not some tricks.

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• jboss connection pooling

  - by Web

  I have a question related to Prepared Steatement pooling (across all connections). Here's the config file <datasources> <local-tx-datasource> <jndi-name>JNDI-NAME</jndi-name> <connection-url>jdbc:mysql://<server_name>/<database_name>?useServerPrepStmts=true</connection-url> <driver-class>com.mysql.jdbc.Driver</driver-class> <user-name>xxx</user-name> <password>xxxxx</password> <min-pool-size>10</min-pool-size> <max-pool-size>20</max-pool-size> <idle-timeout-minutes>20</idle-timeout-minutes> <exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLExceptionSorter</exception-sorter-class-name> <valid-connection-checker-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLValidConnectionChecker</valid-connection-checker-class-name> <background-validation>true</background-validation> <background-validation-minutes>5</background-validation-minutes> <prepared-statement-cache-size>100</prepared-statement-cache-size> <share-prepared-statements>true</share-prepared-statements> <!-- sql to call when connection is created <new-connection-sql>some arbitrary sql</new-connection-sql> --> <!-- sql to call on an existing pooled connection when it is obtained from pool - MySQLValidConnectionChecker is preferred for newer drivers <check-valid-connection-sql>some arbitrary sql</check-valid-connection-sql> --> <!-- corresponding type-mapping in the standardjbosscmp-jdbc.xml --> <metadata> <type-mapping>mySQL</type-mapping> </metadata> </local-tx-datasource> </datasources> It seems that this line: <background-validation-minutes>5</background-validation-minutes> doesn't cause any problems with Prepared Statements, but: <idle-timeout-minutes>20</idle-timeout-minutes> causes that all connections are removed and re-created if there was no traffic for the last 20 minutes. Because of that existing Prepared Statements are removed from the pool of cached Prepared Statements. How to overcome this issue? I have to use idle-timeout-minutes because MySQL server closes the connection after 8h

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• Threading questions

  - by JK

  If I spawn a secondary thread and the threaded method calls other methods, are those methods run in the secondary thread or the main thread? Is there a way to determine on which thread a specified piece of code is being run?

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• Problem while adding a new value to a hashtable when it is enumerated

  - by karthik

  `hi I am doing a simple synchronous socket programming,in which i employed twothreads one for accepting the client and put the socket object into a collection,other thread will loop through the collection and send message to each client through the socket object. the problem is 1.i connect to clients to the server and start send messages 2.now i want to connect a new client,while doing this i cant update the collection and add a new client to my hashtable.it raises an exception "collection modified .Enumeration operation may not execute" how to add a NEW value without having problems in a hashtable. private void Listen() { try { //lblStatus.Text = "Server Started Listening"; while (true) { Socket ReceiveSock = ServerSock.Accept(); //keys.Clear(); ConnectedClients = new ListViewItem(); ConnectedClients.Text = ReceiveSock.RemoteEndPoint.ToString(); ConnectedClients.SubItems.Add("Connected"); ConnectedList.Items.Add(ConnectedClients); ClientTable.Add(ReceiveSock.RemoteEndPoint.ToString(), ReceiveSock); //foreach (System.Collections.DictionaryEntry de in ClientTable) //{ // keys.Add(de.Key.ToString()); //} //ClientTab.Add( //keys.Add( } //lblStatus.Text = "Client Connected Successfully."; } catch (Exception ex) { MessageBox.Show(ex.Message); } } private void btn_receive_Click(object sender, EventArgs e) { Thread receiveThread = new Thread(new ThreadStart(Receive)); receiveThread.IsBackground = true; receiveThread.Start(); } private void Receive() { while (true) { //lblMsg.Text = ""; byte[] Byt = new byte[2048]; //ReceiveSock.Receive(Byt); lblMsg.Text = Encoding.ASCII.GetString(Byt); } } private void btn_Send_Click(object sender, EventArgs e) { Thread SendThread = new Thread(new ThreadStart(SendMsg)); SendThread.IsBackground = true; SendThread.Start(); } private void btnlist_Click(object sender, EventArgs e) { //Thread ListThread = new Thread(new ThreadStart(Configure)); //ListThread.IsBackground = true; //ListThread.Start(); } private void SendMsg() { while (true) { try { foreach (object SockObj in ClientTable.Keys) { byte[] Tosend = new byte[2048]; Socket s = (Socket)ClientTable[SockObj]; Tosend = Encoding.ASCII.GetBytes("FirstValue&" + GenerateRandom.Next(6, 10).ToString()); s.Send(Tosend); //ReceiveSock.Send(Tosend); Thread.Sleep(300); } } catch (Exception ex) { MessageBox.Show(ex.Message); } } }

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• How to interpret Objective-C errors?

  - by Greg Maletic

  I'm getting the following error: 2010-05-11 17:46:28.475 MyApp[54112:5e1b] bool _WebTryThreadLock(bool), 0x140faa0: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now... Is there any way for me to figure out where [54112:5e1b] is in my code, so I can try to narrow down the error? Thanks.

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• Connection hangs after time of inactivity

  - by Sinuhe

  In my application, Spring manages connection pool for database access. Hibernate uses these connections for its queries. At first glance, I have no problems with the pool: it works correctly with concurrent clients and a pool with only one connection. I can execute a lot of queries, so I think that I (or Spring) don't leave open connections. My problem appears after some time of inactivity (sometimes 30 minutes, sometimes more than 2 hours). Then, when Hibernate does some search, it lasts too much. Setting log4j level to TRACE, I get this logs: ... 18:27:01 DEBUG nsactionSynchronizationManager - Retrieved value [org.springframework.orm.hibernate3.SessionHolder@99abd7] for key [org.hibernate.impl.SessionFactoryImpl@7d2897] bound to thread [http-8080-Processor24] 18:27:01 DEBUG HibernateTransactionManager - Found thread-bound Session [org.hibernate.impl.SessionImpl@8878cd] for Hibernate transaction 18:27:01 DEBUG HibernateTransactionManager - Using transaction object [org.springframework.orm.hibernate3.HibernateTransactionManager$HibernateTransactionObject@1b2ffee] 18:27:01 DEBUG HibernateTransactionManager - Creating new transaction with name [com.acjoventut.service.GenericManager.findByExample]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT 18:27:01 DEBUG HibernateTransactionManager - Preparing JDBC Connection of Hibernate Session [org.hibernate.impl.SessionImpl@8878cd] 18:27:01 TRACE SessionImpl - setting flush mode to: AUTO 18:27:01 DEBUG JDBCTransaction - begin 18:27:01 DEBUG ConnectionManager - opening JDBC connection Here it gets frozen for about 2 - 10 minutes. But then continues: 18:30:11 DEBUG JDBCTransaction - current autocommit status: true 18:30:11 DEBUG JDBCTransaction - disabling autocommit 18:30:11 TRACE JDBCContext - after transaction begin 18:30:11 DEBUG HibernateTransactionManager - Exposing Hibernate transaction as JDBC transaction [jdbc:oracle:thin:@212.31.39.50:30998:orcl, UserName=DEVELOP, Oracle JDBC driver] 18:30:11 DEBUG nsactionSynchronizationManager - Bound value [org.springframework.jdbc.datasource.ConnectionHolder@843a9d] for key [org.apache.commons.dbcp.BasicDataSource@7745fd] to thread [http-8080-Processor24] 18:30:11 DEBUG nsactionSynchronizationManager - Initializing transaction synchronization ... After that, it works with no problems, until another period of inactivity. IMHO, it seems like connection pool returns an invalid/closed connection, and when Hibernate realizes that, ask another connection to the pool. I don't know how can I solve this problem or things I can do for delimiting it. Any help achieving this will be appreciate. Thanks. EDIT: Well, it finally was due a firewall rule. Database detects the connection is lost, but pool (dbcp or c3p0) not. So, it tries to query the database with no success. What is still strange for me is that timeout period is very variable. Maybe the rule is specially strange or firewall doesn't work correctly. Anyway, I have no access to that machine and I can only wait for an explanation. :(

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• Does add() on LinkedBlockingQueue notify waiting threads?

  - by obvio171

  I have a consumer thread taking elements from a LinkedBlockingQueue, and I make it sleep manually when it's empty. I use peek() to see if the queue empty because I have to do stuff because sending the thread to sleep, and I do that with queue.wait(). So, when I'm in another thread and add()an element to the queue, does that automatically notify the thread that was wait()ing on the queue?

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• java double buffering problem

  - by russell

  Whats wrong with my applet code which does not render double buffering correctly.I am trying and trying.But failed to get a solution.Plz Plz someone tell me whats wrong with my code. import java.applet.* ; import java.awt.* ; import java.awt.event.* ; public class Ball extends Applet implements Runnable { // Initialisierung der Variablen int x_pos = 10; // x - Position des Balles int y_pos = 100; // y - Position des Balles int radius = 20; // Radius des Balles Image buffer=null; //Graphics graphic=null; int w,h; public void init() { Dimension d=getSize(); w=d.width; h=d.height; buffer=createImage(w,h); //graphic=buffer.getGraphics(); setBackground (Color.black); } public void start () { // Schaffen eines neuen Threads, in dem das Spiel l?uft Thread th = new Thread (this); // Starten des Threads th.start (); } public void stop() { } public void destroy() { } public void run () { // Erniedrigen der ThreadPriority um zeichnen zu erleichtern Thread.currentThread().setPriority(Thread.MIN_PRIORITY); // Solange true ist l?uft der Thread weiter while (true) { // Ver?ndern der x- Koordinate repaint(); x_pos++; y_pos++; //x2--; //y2--; // Neuzeichnen des Applets if(x_pos>410) x_pos=20; if(y_pos>410) y_pos=20; try { Thread.sleep (30); } catch (InterruptedException ex) { // do nothing } Thread.currentThread().setPriority(Thread.MAX_PRIORITY); } } public void paint (Graphics g) { Graphics screen=null; screen=g; g=buffer.getGraphics(); g.setColor(Color.red); g.fillOval(x_pos - radius, y_pos - radius, 2 * radius, 2 * radius); g.setColor(Color.green); screen.drawImage(buffer,0,0,this); } public void update(Graphics g) { paint(g); } } what change should i make.When offscreen image is drawn the previous image also remain in screen.How to erase the previous image from the screen??

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• Mixing .NET versions between website and virtual directories and the "server application unavailable" error Message

  - by Doug Chamberlain

  Backstory Last month our development team created a new asp.net 3.5 application to place out on our production website. Once we had the work completed, we requested from the group that manages are server to copy the app out to our production site, and configure the virtual directory as a new application. On 12/27/2010, two public 'Gineau Pigs' were selected to use the app, and it worked great. On 12/30/2010, We received notification by internal staff, that when that staff member tried to access the application (this was the Business Process Owner) they recieved the 'Server Application Unavailable' message. When I called the group that does our server support, I was told that it probably failed, because I didn't close the connections in my code. However, the same group went in and then created a separate app pool for this Extension Request application. It has had no issues since. I did a little googling, since I do not like being blamed for things. I found that the 'Server Application Unavailable' message will also appear when you have multiple applications using different frameworks and you do not put them in different application pools. Technical Details - Tree of our website structure Main Website <-- ASP Classic +-Virtual Directory(ExtensionRequest) <-- ASP 3.5 From our server support group: 'Reviewed server logs and website setup in IIS. Had to reset the application pool as it was not working properly. This corrected the website and it is now back online. We went ahead and created a application pool for the extension web so it is isolated from the main site pool. In the past we have seen other application do this when there is a connection being left open and the pool fills up. Would recommend reviewing site code to make sure no connections are being left open.' The Real Question: What really caused the failure? Isn't the connection being left open issue an ASP Classic issue? Wouldn't the ExtensionRequest application have to be used (more than twice) in the first place to have the connections left open? Is it more likely the failure is caused by them not bothering to setup the new Application in it's own App Pool in the first place? Sorry for the long windedness

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• Weblogic Error - Method not supported : Statement.cancel

  - by manetic

  I am running an application on Weblogic 9.2 MP3, currently having problem with connection pool. ERROR - UserBean retrieving user record. weblogic.jdbc.extensions.PoolLimitSQLException: weblogic.common.resourcepool.ResourceLimitException: No resources currently available in pool MyApp Data Source to allocate to applications, please increase the size of the pool and retry.. I also kept getting below error message, saying "Method not supported : Statement.cancel()" which I think it is the cause to the error above. <Error> <JDBC> <BEA-001131> <Received an exception when closing a cached statement for the pool "MyApp Data Source": java.sql.SQLException: Method not supported : Statement.cancel()..> I went through the app source code, this method didn't seem to be used by the app at all. Just though it might be something to do with weblogic itself. Anyone have any idea to fix this error?

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