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• The Community-Driven GDB Primer

  - by fbrereto

  I was reading this question and realized it might be helpful for entry- and pro-level developers alike (including myself) to have a common reference for best practices in using gdb. Many questions asked on Stack Overflow could easily be solved by taking some time to step some code in a debugger, and it would be good to have a community-approved resource to "teach them how to fish", so to speak. Even for those seasoned veterans who occasionally find themselves in gdb when they are accustomed to a GUI-tastic debugger might benefit from those who are much more familiar with the command line tool. For starters (both to gdb and to prime this thread) I submit: Ninefinger's gdb primer The gdb quick reference guide, which is useful for telling you what commands are available but not how best to use them. My hope is this thread is a seed planted that is of continued value to the community. If by "continued value" the community decides to nix it altogether, well then the masses have spoken.

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• Threading in java

  - by Mohd Adnan

  THREAD make the run time environment asynchronous. kindly elaborate the above line?

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• openmp in mex : stackoverflow error

  - by Edwin

  i have got the following fraction of code that getting me the stack overflow error #pragma omp parallel shared(Mo1, Mo2, sum_normalized_p_gn, Data, Mean_Out,Covar_Out,Prior_Out, det) private(i) num_threads( number_threads ) { //every thread has a new copy double* normalized_p_gn = (double*)malloc(NMIX*sizeof(double)); #pragma omp critical { int id = omp_get_thread_num(); int threads = omp_get_num_threads(); mexEvalString("drawnow"); } #pragma omp for //some parallel process..... } the variables declared in the shared are created by malloc. and they consumes with large amount of memory there are 2 questions regarding to the above code. 1) why this would generate the stack overflow error( i.e. segmentation fault) before it goes into the parallel for loop? it works fine when it runs in the sequential mode.... 2) am i right to dynamic allocate memory for each thread like "normalized_p_gn" above? Regards Edwin

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• POSIX threads and signals

  - by Donal Fellows

  I've been trying to understand the intricacies of how POSIX threads and POSIX signals interact. In particular, I'm interested in: What's the best way to control which thread a signal is delivered to (assuming it isn't fatal in the first place)? What is the best way to tell another thread (that might actually be busy) that the signal has arrived? (I already know that it's a bad idea to be using pthread condition variables from a signal handler.) For reference about why I want this, I'm researching how to convert the TclX package to support threads, or to split it up and at least make some useful parts support threads. Signals are one of those parts that is of particular interest.

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• C# TraceSource class in multithreaded application

  - by matti

  msdn: "Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." it contains only instance methods. How should I use it in a way that all activity gets recorder by TextWriterTraceListener to a text file. Is one static member which all threads use (by calling) TraceEvent-method safe. (I've kind of asked this question in http://stackoverflow.com/questions/1901086/how-to-instantiate-c-tracesources-to-log-multithreaded-asp-net-2-0-web-applica, but I cannot just believe if somebody just says it's OK despite the documentation).

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• how to debug ExceptionInInitializationError?

  - by grmn.bob

  I am getting an exception in a very simple 'study' application, so I expect the problem to be in my project setup, but I don't know how to debug ... What is the context of the exception, "ExceptionInInitializationError"? Where is it documented? A: Search Android Developers Guide Stack trace from within Eclipse Debugger with: select thread - right-click - copy stack Thread [<3> main] (Suspended (exception ExceptionInInitializerError)) Class.newInstance() line: 1479 Instrumentation.newActivity(ClassLoader, String, Intent) line: 1021 ActivityThread.performLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2367 ActivityThread.handleLaunchActivity(ActivityThread$ActivityRecord, Intent) line: 2470 ActivityThread.access$2200(ActivityThread, ActivityThread$ActivityRecord, Intent) line: 119 ActivityThread$H.handleMessage(Message) line: 1821 ActivityThread$H(Handler).dispatchMessage(Message) line: 99 Looper.loop() line: 123 ActivityThread.main(String[]) line: 4310 Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method] Method.invoke(Object, Object...) line: 521 ZygoteInit$MethodAndArgsCaller.run() line: 860 ZygoteInit.main(String[]) line: 618 NativeStart.main(String[]) line: not available [native method]

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• what is coroutine?

  - by dorelal

  coroutine appears in this nodejs thread. http://groups.google.com/group/nodejs/msg/df199d233ff17efa

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• In a multithreaded app, would a multi-core or multiprocessor arrangement be better?

  - by Michael

  I've read a lot on this topic already both here (e.g., stackoverflow.com/questions/1713554/threads-processes-vs-multithreading-multi-core-multiprocessor-how-they-are or http://stackoverflow.com/questions/680684/multi-cpu-multi-core-and-hyper-thread) and elsewhere (e.g., ixbtlabs.com/articles2/cpu/rmmt-l2-cache.html or software.intel.com/en-us/articles/multi-core-introduction/), but I still am not sure about a couple things that seem very straightforward. So I thought I'd just ask. (1) Is a multi-core processor in which each core has dedicated cache effectively the same as a multiprocessor system (balanced of course for processor speed, cache size, and so on)? (2) Let's say I have some images to analyze (i.e., computer vision), and I have these images loaded into RAM. My app spawns a thread for each image that needs to be analyzed. Will this app on a shared cache multi-core processor run slower than on a dedicated cache multi-core processor, and would the latter run at the same speed as on an equivalent single-core multiprocessor machine? Thank you for the help!

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• Asynchronous Silverlight WCF callback

  - by Matt

  I've created my own WCF service and I've successfully been able to talk to it via my Silverlight client. I ran into an interesting problem on my asynchronous callbacks though. When my callback is invoked, I can't update any UI controls with the dreaded invalid cross thread access Here's what my callback function looks like private void GetTimeCallBack( object sender, Talk.ClientBase<IService>.ClientEventArgs e ) { lblDisplay.Text = e.Object.ToString(); } A quick google search showed me that I have to do this instead. private void GetTimeCallBack( object sender, Talk.ClientBase<IService>.ClientEventArgs e ) { Dispatcher.BeginInvoke( () => lblDisplay.Text = e.Object.ToString() ); } Now everything works fine, but I wasn't expecting my callback to be running on a different thread. Will I always have to use the Dispatcher class in order to modify anything within my class or is this just limited to UI elements? I've not familiar with the Dispatcher class at all so I'm looking to understand it more.

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• asp.net InsertCommand to return latest insert ID

  - by Stijn Van Loo

  Dear all, I'm unable to retrieve the latest inserted id from my SQL Server 2000 db using a typed dataset in asp.NET I have created a tableadapter and I ticked the "Refresh datatable" and "Generate Insert, Update and Delete statements". This auto-generates the Fill and GetData methods, and the Insert, Update, Select and Delete statements. I have tried every possible solution in this thread http://forums.asp.net/t/990365.aspx but I'm still unsuccesfull, it always returns 1(=number of affected rows). I do not want to create a seperate insert method as the auto-generated insertCommand perfectly suits my needs. As suggested in the thread above, I have tried to update the InsertCommand SQL syntax to add SELECT SCOPY_IDENTITY() or something similar, I have tried to add a parameter of type ReturnValue, but all I get is the number of affected rows. Does anyone has a different take on this? Thanks in advance! Stijn

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• Is writing a reference atomic on 64bit VMs

  - by Steffen Heil

  Hi The java memory model mandates that writing a int is atomic: That is, if you write a value to it (consisting of 4 bytes) in one thread and read it in another, you will get all bytes or none, but never 2 new bytes and 2 old bytes or such. This is not guaranteed for long. Here, writing 0x1122334455667788 to a variable holding 0 before could result in another thread reading 0x112233440000000 or 0x0000000055667788. Now the specification does not mandate object references to be either int or long-sized. For type safety reasons I suspect they are guaranteed to be written atomiacally, but on a 64bit VM these references could be very well 64bit values (merely memory addresses). No here are my question: Are there any memory model specs covering this (that I haven't found)? Are long-writes suspect to be atomic on 64bit VMs? Are VMs forced to map references to 32bit? Regards, Steffen

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• slide animation skipped when using updatepanel callback

  - by superexsl

  Hey, I'm trying to use UpdatePanels and JQuery but the panels seem to cancel out the JQuery. I want the user to press the search button, have the system perform the search using AJAX and then display the search results by sliding down the div using JQuery. However, it seems that if there are any delays, (I put the thread to sleep for a second), then the results just appear instead of sliding down. If I remove the sleep thread the sliding animation is fine. I've got the code below to execute the JQuery once the AJAX is loaded: <script type="text/javascript"> var prm = Sys.WebForms.PageRequestManager.getInstance(); prm.add_pageLoaded(showDiv); function showDiv(sender, args){ $("#results_bar").slideDown('slow'); } </script> Any ideas why the animation is skipped if there's a delay? Thanks

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• Do Scala and Erlang use green threads?

  - by CHAPa

  I've been reading a lot about how Scala and Erlang does lightweight threads and their concurrency model (actors). However, I have my doubts. Do Scala and Erlang use an approach similar to the old thread model used by Java (green threads) ? For example, suppose that there is a machine with 2 cores, so the Scala/Erlang environment will fork one thread per processor? The other threads will be scheduled by user-space (Scala VM / Erlang VM ) environment. Is this correct? Under the hood, how does this really work?

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• Adding info to an exception

  - by NoozNooz42

  I'd like to add information to a stack trace/exception. Basically I've got something like this as of now, which I really like: Exception in thread "main" java.lang.ArithmeticException: / by zero at com.so.main(SO.java:41) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke However I'd like to catch that exception and add additional info to it, while still having the original stack trace. For example, I'd like to have that: Exception in thread "main" CustomException: / by zero (you tried to divide 42 by 0) at com.so.main(SO.java:41) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke So basically I want to catch the ArithmeticException and rethrow, say, a CustomException (adding "you tried to divide 42 by 0" in this example) while still keeping the stacktrace from the original ArithmeticException. What is the correct way to do this in Java? Is the following correct: try { .... } catch (ArithmeticException e) { throw new CustomException( "You tried to divide " + x + " by " + y, e ); }

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• Problem with stackless python, cannot write to a dict

  - by ANON

  I have simple map-reduce type algorithm, which I want to implement in python and make use of multiple cores. I read somewhere that threads using native thread module in 2.6 dont make use of multiple cores. is that true? I even implemented it using stackless python however i am getting into weird errors [Update: a quick search showed that the stack less does not allows multiple cores So are their any other alternatives?] def Propagate(start,end): print "running Thread with range: ",start,end def maxVote(nLabels): count = {} maxList = [] maxCount = 0 for nLabel in nLabels: if nLabel in count: count[nLabel] += 1 else: count[nLabel] = 1 #Check if the count is max if count[nLabel] > maxCount: maxCount = count[nLabel]; maxList = [nLabel,] elif count[nLabel]==maxCount: maxList.append(nLabel) return random.choice(maxList) for num in range(start,end): node=MapList[num] nLabels = [Label[k] for k in Adj[node]] if (nLabels!=[]): Label[node] = maxVote(nLabels) else: Label[node]=node However in above code the values assigned to Label, that is the change in dictionary are lost. Above propagate function is used as callable for MicroThreads (i.e. TaskLets)

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• Nested resources in namespace form_for

  - by Nelson LaQuet

  Problem The form_for helper incorrectly determines the path to my nested resource inside of a namespace. The models in question are: Forum::Thread and Forum::Reply respectively, located in a subfolder called "forum" under my models directory. This is in Rails 3 BETA 3. routes.rb namespace :forum do root :to => 'threads#index' resources :threads do resources :replies end end app/views/forum/replies/_form.html.haml ... - form_for [@thread, @reply] do |f| ... app/controllers/forum/replies_controller.rb ... def new @reply = Forum::Reply.new end ... Error undefined method `forum_thread_forum_replies_path' In reference to the line outlined above in _form.html.haml

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• C# CultureInfo NumberFormat NumberDecimalSeparator Problem

  - by Mahdi

  I want to change NumberDecimalSeparator of my application from "." to "/". it works when i show float numbers in my textbox. but integer types are not shown at all. I modify thread's culture to get application-wide formatting. my code is like this: CultureInfo ci = new CultureInfo("fa-IR", true); ci.NumberFormat.DigitSubstitution = DigitShapes.NativeNational; ci.NumberFormat.NumberDecimalSeparator = "/"; Thread.CurrentThread.CurrentCulture = ci; result: 3.14 = "3/14" 100 = "" Any help please ?

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• Java - SwingWorker - Can we call one SwingWorker from other SwingWorker instead of EDT

  - by Yatendra Goel

  I have a SwingWorker as follows: public class MainWorker extends SwingWorker(Void, MyObject) { : : } I invoked the above Swing Worker from EDT: MainWorker mainWorker = new MainWorker(); mainWorker.execute(); Now, the mainWorker creates 10 instances of a MyTask class so that each instance will run on its own thread so as to complete the work faster. But the problem is I want to update the gui from time to time while the tasks are running. I know that if the task was executed by the mainWorker itself, I could have used publish() and process() methods to update the gui. But as the tasks are executed by threads different from the Swingworker thread, how can I update the gui from intermediate results generated by threads executing tasks.

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• Three20 - add items to launcherView after viewDidLoad

  - by lostInTransit

  Hi I am getting a list of image URLs and corresponding names at run time in my app. I would like to add these images to a TTLauncherView object that I have. Cannot add these in loadView. I am making a call to the method for getting my data in a separate thread. Once the thread completes, I add the TTLauncherItem objects to an array and set the "pages" variable of the LauncherView. But for some reason, the view is not updated and I don't see anything on it. Can someone please let me know how to refresh the launcherview after adding items to it in methods other than loadView? Thanks.

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• What is best practice with SQLite and Android ?

  - by PHP_Jedi

  What is considered "best practice" when executing queries on a sql-lite db within an android app. Is it safe to run inserts, deletes and select queries from an AsyncTask's doInBackground ? Or should I use the UI Thread ? I suppose that db queries can be "heavy" and should not use the UI thread as it can lock up the app - resulting in an ANR. If I have several AsyncTasks, should they share a connection or should they open a connection each ? Any best practices in this area on android?

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• QProcess, QEventLoop - of any use for parallel-processing

  - by dlib

  I wonder whether I could use QEventLoop (QProcess?) to parallelize multiple calls to same function with Qt. What is precisely the difference with QtConcurrent or QThread? What is a process and an event loop more precisely? I read that QCoreApplication must exec() as early as possible in main() method, so that I wonder why it is different from main Thread. could you point as some efficient reference to processes and thread with Qt? I came through the official doc and those things remain unclear. Thanks and regards.

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• How to solve the Winforms Control.Invoke Error?

  - by omn ohnmar

  How to solve the "Control.Invoke must be used to interact with controls created on a separated thread" Error Exception

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• VS2010 + Resharper 5 performance issues

  - by Jeremy Roberts

  I have been using VS2010 with Resharper 5 for several weeks and am having a performance issue. Sometimes when typing, the cursor will lag and the keystrokes won't show instantaneously. Also, scrolling will lag at times. There is a forum thread started and JetBrains has been responding. Several people (including myself) have added their voice and uploaded some performance profiles. If anyone here has has this issue, I would encourage you to visit the thread and let JetBrains know about it. Has anyone had this problem and have a suggestion to restore performance?

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• Creating a dynamic (video) Overlay on Google Maps on Android 2.1

  - by Soumya

  I'm trying to create a map overlay for displaying a video stream (MJPEG) on top of a Mapview. Currently I've a standalone activity that creates a data thread for fetching MJPEG video frames. I'm using a handler to send a frame (as a Bitmap) from the data thread to the main activity which then updates the UI. I'm not sure how I can implement "refresh" for updating my "overlayed" video stream. EDIT: What I mean by "refresh" is - how can I update the video portion (not the mapview) of my UI whenever I get a new video frame. I plan to paint the video frame (bitmap) in the "draw method" of my implementation of the Overlay subclass. But the "draw" method is not invoked by me directly. Thanks.

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• Scala/Erlang use something like greenThread or not ?

  - by CHAPa

  Hi all, Im reading a lot about how scala/Erlang does lightweight threads and your concurrency model ( Actor Model ). Off course, some doubts appear in my head. Scala/Erlang use a approach similar to the old thread model used by java (greenThread) ? for example, suppose that there is a machine with 2 cores, so the scala/erlang environment will fork one thread per processor ? The other threads will be scheduled by user-space( scala VM / erlang vm ) environment. is it correct ? how under the hood that really work ? thanks a lot.

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