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  • Basic Java Multi-Threading Question

    - by Veered
    When an object is instantiated in Java, is it bound to the thread that instantiated in? Because when I anonymously implement an interface in one thread, and pass it to another thread to be run, all of its methods are run in the original thread. If they are bound to their creation thread, is there anyway to create an object that will run in whatever thread calls it?

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  • WaitForSingleObject( )

    - by Rakesh Agarwal
    I have got myself stuck into a really amazing issue here.The code is like as below. class A { public: A(){ m_event = CreateEvent(NULL, false, false, NULL); // create an event with initial value as non-signalled m_thread = _beginthread(StaticThreadEntry, 0, this); // create a thread } static void StaticThreadEntry(A * obj) { obj->ThreadEntry(); } void ThreadEntry(); }; void A::ThreadEntry() { WaitforSingleObject(m_event,INFINITE); } int main() { A a; SetEvent(m_event); // sets the event to signalled state which causes the running thread to terminate WaitForSingleObject(m_thread, INFINITE); // waits for the thread to terminate return 0; } Problem : When the above code is run,sometimes( 1 out of 5 ) it hangs and the control gets stuck in the call to WaitforSingleObject()( inside the main function ).The code always calls SetEvent() function to ensure that the thread would terminate before calling Wait() function. I do not see any reason why it should ever hang?

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  • Swing: what to do when a JTree update takes too long and freezes other GUI elements?

    - by java.is.for.desktop
    Hello, everyone! I know that GUI code in Java Swing must be put inside SwingUtilities.invokeAndWait or SwingUtilities.invokeLater. This way threading works fine. Sadly, in my situation, the GUI update it that thing which takes much longer than background thread(s). More specific: I update a JTree with about just 400 entries, nesting depth is maximum 4, so should be nothing scary, right? But it takes sometimes one second! I need to ensure that the user is able to type in a JTextPane without delays. Well, guess what, the slow JTree updates do cause delays for JTextPane during input. It refreshes only as soon as the tree gets updated. I am using Netbeans and know empirically that a Java app can update lots of information without freezing the rest of the UI. How can it be done? NOTE 1: All those DefaultMutableTreeNodes are prepared outside the invokeAndWait. NOTE 2: When I replace invokeAndWait with invokeLater the tree doesn't get updated. NOTE 3: Fond out that recursive tree expansion takes far the most time. NOTE 4: I'm using custom tree cell renderer, will try without and report. NOTE 4a: My tree cell renderer uses a map to cache and reuse created JTextComponents, depending on tree node (as a key). CLUE 1: Wow! Without setting custom cell renderer it's 10 times faster. I think, I'll need few good tutorials on writing custom tree cell renderers.

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  • Parallelism in Python

    - by fmark
    What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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  • How to simulate an unhandled exception in Java

    - by Martin Wiboe
    Hi, I am creating some multi-threaded code, and I have created a JobDispatcher class that creates threads. I want this object to handle any unhandled exceptions in the worker threads, and so I am using Thread.setUncaughtExceptionHandler(this); Now, I would like to test this functionality - how can I generate an unhandled exception in the run() method of my worker object? Thanks, Martin

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  • Variable mysteriously changing value

    - by Eitan
    I am making a simple tcp/ip chat program for practicing threads and tcp/ip. I was using asynchronous methods but had a problem with concurrency so I went to threads and blocking methods (not asynchronous). I have two private variables defined in the class, not static: string amessage = string.Empty; int MessageLength; and a Thread private Thread BeginRead; Ok so I call a function called Listen ONCE when the client starts: public virtual void Listen(int byteLength) { var state = new StateObject {Buffer = new byte[byteLength]}; BeginRead = new Thread(ReadThread); BeginRead.Start(state); } and finally the function to receive commands and process them, I'm going to shorten it because it is really long: private void ReadThread(object objectState) { var state = (StateObject)objectState; int byteLength = state.Buffer.Length; while (true) { var buffer = new byte[byteLength]; int len = MySocket.Receive(buffer); if (len <= 0) return; string content = Encoding.ASCII.GetString(buffer, 0, len); amessage += cleanMessage.Substring(0, MessageLength); if (OnRead != null) { var e = new CommandEventArgs(amessage); OnRead(this, e); } } } Now, as I understand it only one thread at a time will enter BeginRead, I call Receive, it blocks until I get data, and then I process it. The problem: the variable amessage will change it's value between statements that do not touch or alter the variable at all, for example at the bottom of the function at: if (OnRead != null) "amessage" will be equal to 'asdf' and at if (OnRead != null) "amessage" will be equal to qwert. As I understand it this is indicative of another thread changing the value/running asynchronously. I only spawn one thread to do the receiving and the Receive function is blocking, how could there be two threads in this function and if there is only one thread how does amessage's value change between statements that don't affect it's value. As a side note sorry for spamming the site with these questions but I'm just getting a hang of this threading story and it's making me want to sip cyanide. Thanks in advance. EDIT: Here is my code that calls the Listen Method in the client: public void ConnectClient(string ip,int port) { client.Connect(ip,port); client.Listen(5); } and in the server: private void Accept(IAsyncResult result) { var client = new AbstractClient(MySocket.EndAccept(result)); var e = new CommandEventArgs(client, null); Clients.Add(client); client.Listen(5); if (OnClientAdded != null) { var target = (Control) OnClientAdded.Target; if (target != null && target.InvokeRequired) target.Invoke(OnClientAdded, this, e); else OnClientAdded(this, e); } client.OnRead += OnRead; MySocket.BeginAccept(new AsyncCallback(Accept), null); } All this code is in a class called AbstractClient. The client inherits the Abstract client and when the server accepts a socket it create's it's own local AbstractClient, in this case both modules access the functions above however they are different instances and I couldn't imagine threads from different instances combining especially as no variable is static.

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  • Insert Comment Reply Form Into Page Using Jquery

    - by Joe
    I have been making a threaded comment system as a way to learn php and javascript/jquery properly. Ive done bits and bobs in the past but ive made a new years resolution to learn it properly. Im having trouble inserting a reply form into the comment tree below the comment being replied to. I know this is probably pretty basic but how do you insert html into a page when someone clicks a link. This code wasn't working for me: $(document).ready(function(){ $(function() { $('a#reply').click(function() { $(this).append("the html blah"); }); }); }); Anyone see where im going wrong?

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  • How do I start up an NSRunLoop, and ensure that it has an NSAutoreleasePool that gets emptied?

    - by Nick Forge
    I have a "sync" task that relies on several "sub-tasks", which include asynchronous network operations, but which all require access to a single NSManagedObjectContext. Due to the threading requirements of NSManagedObjectContexts, I need every one of these sub-tasks to execute on the same thread. Due to the amount of processing being done in some of these tasks, I need them to be on a background thread. At the moment, I'm launching a new thread by doing this in my singleton SyncEngine object's -init method: [self performSelectorInBackground:@selector(initializeSyncThread) withObject:nil]; The -initializeSyncThread method looks like this: - (void)initializeSyncThread { self.syncThread = [NSThread currentThread]; self.managedObjectContext = [(MyAppDelegate *)[UIApplication sharedApplication].delegate createManagedObjectContext]; NSRunLoop *runLoop = [NSRunLoop currentRunLoop]; [runLoop run]; } Is this the correct way to start up the NSRunLoop for this thread? Is there a better way to do it? The run loop only needs to handle 'performSelector' sources, and it (and its thread) should be around for the lifetime of the process. When it comes to setting up an NSAutoreleasePool, should I do this by using Run Loop Observers to create the autorelease pool and drain it after every run-through?

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  • Advantage of using Thread.Start vs QueueUserWorkItem

    - by Cheeso
    In multithreaded .NET programming, what are the decision criteria for using ThreadPool.QueueUserWorkItem versus starting my own thread via new Thread() and Thread.Start()? In a server app (let's say, an ASP.NET app or a WCF service) I think the ThreadPool is always there and available. What about in a client app, like a WinForms or WPF app? Is there a cost to spin up the thread pool? If I just want 3 or 4 threads to work for a short period on some computation, is it better to QUWI or to Thread.Start().

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  • What is difference between Thread Affinity and Process affinity ?

    - by DotNetBeginner
    What is difference between Thread Affinity and Process affinity ? If I have two Threads and I have duel core machine then is it possible to run these two threads parallely on the two cores ? If I use processor affinity Mask then I can control execution of a process on the cores but when I have to run threads on a particular core how can I make these threads core specific ? A very simple example will be appreciated.

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  • Java - How to detect that the internet connection has got disconnected through a java desktop applic

    - by Yatendra Goel
    I am developing a Java Desktop Application that access internet. It is a multi-threaded application, each thread do the same work (means each thread is an instance of same Thread class). Now, as all the threads need internet connection to be active, there should be some mechanism that detects whether an internet connection is active or not. Q1. How to detect whether the internet connection is active or not? Q2. Where to implement this internet-status-check-mechanism code? Should I start a separate thread for checking internet status regularly and notifies all the threads when the status changes from one state to another? Or should I let each thread check for the internet-status itself? Q3. This issue should be a very common issue as every application accessing an internet should deal with this problem. So how other developers usually deal with this problem? Q4. If you could give me a reference to a good demo application that addresses this issue then it would greatly help me.

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  • How to open AsyncTask from a Thread

    - by Abhishek
    In my application I have created a SplashScreen that will b shown for 5 Seconds and after that it executes an if else case depending upon the values stored in the Preference file. If Preference file contains values then the AsyncTask code will run else the Login form will load. When i try to run my application. The thread is going to the Login form with the help of intent but when it comes to AsyncTask my application shows a force close error message. This is my SplashScreen code: public class SplashScreen extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); setContentView(R.layout.splashscreen); Thread timer = new Thread() { public void run() { try { sleep(5000); } catch(InterruptedException e) { e.printStackTrace(); } finally { if(GoGolfPref.getEmail(SplashScreen.this)!=null && GoGolfPref.getPass(SplashScreen.this)!=null) { new LoadingScreen(SplashScreen.this, SplashScreen.this).execute("login_page", Login.url+GoGolfPref.getEmail(SplashScreen.this)+"/"+GoGolfPref.getPass(SplashScreen.this)); } else { Intent in = new Intent(SplashScreen.this, Login.class); startActivity(in); finish(); } } } }; timer.start(); } } This is the error I am getting: 08-29 07:25:58.040: E/AndroidRuntime(2365): FATAL EXCEPTION: Thread-10 08-29 07:25:58.040: E/AndroidRuntime(2365): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare() 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.os.Handler.<init>(Handler.java:121) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.Dialog.<init>(Dialog.java:101) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.AlertDialog.<init>(AlertDialog.java:63) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.ProgressDialog.<init>(ProgressDialog.java:80) 08-29 07:25:58.040: E/AndroidRuntime(2365): at android.app.ProgressDialog.<init>(ProgressDialog.java:76) 08-29 07:25:58.040: E/AndroidRuntime(2365): at com.pnf.gogolf.LoadingScreen.<init>(LoadingScreen.java:130) 08-29 07:25:58.040: E/AndroidRuntime(2365): at com.pnf.gogolf.SplashScreen$1.run(SplashScreen.java:32) How to get this working? Thanks in advance...

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  • How to indefinitely pause a thread in Java and later resume it?

    - by Carlos Torres
    Maybe this question has been asked many times before, but I never found a satisfying answer. The problem: I have to simulate a process scheduler, using the round robin strategy. I'm using threads to simulate processes and multiprogramming; everything works fine with the JVM managing the threads. But the thing is that now I want to have control of all the threads so that I can run each thread alone by a certain quantum (or time), just like real OS processes schedulers. What I'm thinking to do: I want have a list of all threads, as I iterate the list I want to execute each thread for their corresponding quantum, but as soon the time's up I want to pause that thread indefinitely until all threads in the list are executed and then when I reach the same thread again resume it and so on. The question: So is their a way, without using deprecated methods stop(), suspend(), or resume(), to have this control over threads?

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  • Thread Local Storage and local method variables

    - by miguel
    In c#, each thread has its own stack space. If this is the case, why is the following code not thread-safe? (It is stated that this code is thread-safe on this post: Locking in C# class Foo { private int count = 0; public void TrySomething() { count++; } } As count is an int (stack variable), surely this value would be isolated to an individual thread, on its own stack, and therefore thread-safe? I am probably missing something here, but I dont understand what is actually in Thread Local Storage if not stack-based variables for the thread?

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  • C# Threading vs single thread

    - by user177883
    Is it always guaranteed that a multi-threaded application would run faster than a single threaded application? I have two threads that populates data from a data source but different entities (eg: database, from two different tables), seems like single threaded version of the application is running faster than the version with two threads. Why would the reason be? when i look at the performance monitor, both cpu s are very spikey ? is this due to context switching? what are the best practices to jack the CPU and fully utilize it? I hope this is not ambiguous.

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  • Testing a Non-blocking Queue

    - by jsw
    I've ported the non-blocking queue psuedocode here to C#. The code below is meant as a near verbatim copy of the paper. What approach would you take to test the implementation? Note: I'm running in VS2010 so I don't have CHESS support yet. using System.Threading; #pragma warning disable 0420 namespace ConcurrentCollections { class QueueNodePointer<T> { internal QueueNode<T> ptr; internal QueueNodePointer() : this(null) { } internal QueueNodePointer(QueueNode<T> ptr) { this.ptr = ptr; } } class QueueNode<T> { internal T value; internal QueueNodePointer<T> next; internal QueueNode() : this(default(T)) { } internal QueueNode(T value) { this.value = value; this.next = new QueueNodePointer<T>(); } } public class ConcurrentQueue<T> { private volatile int count = 0; private QueueNodePointer<T> qhead = new QueueNodePointer<T>(); private QueueNodePointer<T> qtail = new QueueNodePointer<T>(); public ConcurrentQueue() { var node = new QueueNode<T>(); node.next.ptr = null; this.qhead.ptr = this.qtail.ptr = node; } public int Count { get { return this.count; } } public void Enqueue(T value) { var node = new QueueNode<T>(value); node.next.ptr = null; QueueNodePointer<T> tail; QueueNodePointer<T> next; while (true) { tail = this.qtail; next = tail.ptr.next; if (tail == this.qtail) { if (next.ptr == null) { var newtail = new QueueNodePointer<T>(node); if (Interlocked.CompareExchange(ref tail.ptr.next, newtail, next) == next) { Interlocked.Increment(ref this.count); break; } else { Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } } } } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(node), tail); } public T Dequeue() { T value; while (true) { var head = this.qhead; var tail = this.qtail; var next = head.ptr.next; if (head == this.qhead) { if (head.ptr == tail.ptr) { if (next.ptr == null) { return default(T); } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } else { value = next.ptr.value; var newhead = new QueueNodePointer<T>(next.ptr); if (Interlocked.CompareExchange(ref this.qhead, newhead, head) == head) { Interlocked.Decrement(ref this.count); break; } } } } return value; } } } #pragma warning restore 0420

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  • Is SynchronizationContext.Post() threadsafe?

    - by cyclotis04
    This is a pretty basic question, and I imagine that it is, but I can't find any definitive answer. Is SynchronizationContext.Post() threadsafe? I have a member variable which holds the main thread's context, and _context.Post() is being called from multiple threads. I imagine that Post() could be called simultaneously on the object. Should I do something like lock (_contextLock) _context.Post(myDelegate, myEventArgs); or is that unnecessary? Edit: MSDN states that "Any instance members are not guaranteed to be thread safe." Should I keep my lock(), then?

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  • Cocoa Touch - Display an Activity Indicator while loading a UITabBar View

    - by Aurum Aquila
    I have a UITabBar Application with two views that load large amounts of data from the web in their "viewWillAppear" methods. I want to show a progress bar or an activity indicator while this data is being retrieved, to make sure the user knows the app isn't frozen. I am aware that this has been asked before. I simply need some clarification on what seems to be a rather good solution. I have implimented the code in the example. The question's original asker later solved their problem, by putting the retrieval of data into another "thread". I understand the concept of threads, but I do not know how I would impliment this. With research, I have found that I need to move all of my heavy data retrieval into a background thread, as all of the UI updating occurs in the main thread. If one would be so kind as to provide an example for me, I would be very appreciative. I can provide parts of my existing code as necessary.

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  • Why can't I use an Action to a ThreadStart?

    - by Rookian
    Both are delegates and have the same signature, but I can not use Action as ThreadStart. Why? Action doIt; doIt = () => MyMethod("test"); Thread t; t = new Thread(doIt); t.Start(); but this seams to work: Thread t; t = new Thread(() => MyMethod("test")); t.Start();

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  • Is it possible to store pointers in shared memory without using offsets?

    - by Joseph Garvin
    When using shared memory, each process may mmap the shared region into a different area of their address space. This means that when storing pointers within the shared region, you need to store them as offsets of the start of the shared region. Unfortunately, this complicates use of atomic instructions (e.g. if you're trying to write a lock free algorithm). For example, say you have a bunch of reference counted nodes in shared memory, created by a single writer. The writer periodically atomically updates a pointer 'p' to point to a valid node with positive reference count. Readers want to atomically write to 'p' because it points to the beginning of a node (a struct) whose first element is a reference count. Since p always points to a valid node, incrementing the ref count is safe, and makes it safe to dereference 'p' and access other members. However, this all only works when everything is in the same address space. If the nodes and the 'p' pointer are stored in shared memory, then clients suffer a race condition: x = read p y = x + offset Increment refcount at y During step 2, p may change and x may no longer point to a valid node. The only workaround I can think of is somehow forcing all processes to agree on where to map the shared memory, so that real pointers rather than offsets can be stored in the mmap'd region. Is there any way to do that? I see MAP_FIXED in the mmap documentation, but I don't know how I could pick an address that would be safe.

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  • How to re-use a thread in Java ?

    - by David
    I am a building a console Sudoku Solver where the main objective is raw speed. I now have a ManagerThread that starts WorkerThreads to compute the neibhbors of each cell. So one WorkerThread is started for each cell right now. How can I re-use an existing thread that has completed its work? The Thread Pool Pattern seems to be the solution, but I don't understand what to do to prevent the thread from dying once its job has been completed. ps : I do not expect to gain much performance for this particular task, just want to experiment how multi-threading works before applying it to the more complex parts of the code. Thanks

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  • C# Threads.Abort()

    - by Betamoo
    If a thread is running a function func1 that calls another function func2 inside it... Then I called thread.Abort() Will this stop func1 only OR func1 and func2 and all the functions func1 has called?? Thanks Edit: Here are more detail: func1 is called in a new thread, it continuously calls func2 on regular basis... func2 begin doing some work only if some array is not null.. it finishes it and return When supervisor wants to save data, it aborts Thread of func1- and then makes array null, saves data, then fill in the array with new one.. and starts Thread with func1 again.. Sometimes exception is raised because array is null in func2.. so func1 abort did not affect func2

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