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• Thread-safe get (accessor method)

  - by sonofdelphi

  I'm currently using the following code for thread-safe access of a variable. int gnVariable; void getVariableValue(int *pnValue) { acquireLock(); //Acquires the protection mechanism *pnValue = gnVariable; releaseLock(); //Releasing the protection mechanism } I would like to change my API signature to a more user-friendly int getVariableValue(void); How should I rewrite the function - such that the users of the API don't have to bother about the locking/unlocking details?

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• Real World Examples of read-write in concurrent software

  - by Richard Fabian

  I'm looking for real world examples of needing read and write access to the same value in concurrent systems. In my opinion, many semaphores or locks are present because there's no known alternative (to the implementer,) but do you know of any patterns where mutexes seem to be a requirement? In a way I'm asking for candidates for the standard set of HARD problems for concurrent software in the real world.

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• How to tell if there is an available thread in a thread pool in java

  - by Gormcito

  I am trying to proccess a queue of tasks from a database table as fast as possible while also limiting the number of threads to process the tasks. I am using a fixed sized thread pool with Executors.newFixedThreadPool(N); I want to know if there is a way of knowing if the thread pool is full, by that I mean are there currently 50 threads running, if so then I'll wait for a thread to be available before starting a new one instead of sleeping the main thread. Code of what I would like to do: ExecutorService executor = Executors.newFixedThreadPool(N); ResultSet results; while( true ) { results = getWaitingTasksStmt.executeQuery(); while( results.next() && executor.notFull() ) { executor.submit( new thread( new runnableInheritedClass(results) ) ); } }

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• Thread toggling

  - by sid

  Hi all, In Ubuntu, I am running 2 'C' applications, When I press key up/down the applications are alternatively getting the events. What might be the problem/solution? Ex: I have 'A application' and 'B application', I launch 'A application' and press the key up/down its working fine. If I simultaneously launch 'B application' and focus is on 'B application' then pressing key up/down will toggle between 'A application' & 'B application' so 2 times I have to press the key to move on 'B application'(focus is on 'B application'). 'A application' and 'B application' are threads. Thanks in advance-opensid

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• unprotected access to member in property get

  - by Lenik

  I have a property public ObservableCollection<string> Name { get { return _nameCache; } } _nameCache is updated by multiple threads in other class methods. The updates are guarded by a lock. The question is: should I use the same lock around my return statement? Will not using a lock lead to a race condition?

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• [java] run 2 threads simultaneously

  - by lamsaitat

  hi all, in the case of an IM client. i have made 2 separate threads to handle sending packets (by std io) and receiving packets. the question is how to make these 2 threads run simultaneously so that i can keep prompting for input while at the same time be ready to receive packets at any time? i have already tried setting a timer but the data is always lost receiving.

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• C# start a static thread

  - by user595605

  I have a Queue of items I want to process in a thread, and any instance of a class can add items to the Queue to be processed. My idea for doing this is to have a static Thread in the class that processes the items, the only problem is that I don't know where to start this thread, since I can't start it in its initialization. Is there a way I can start a static thread? Or should I be changing the architecture completely?

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• Queues And Wait Handles in C#

  - by Michael Covelli

  I've had the following code in my application for some years and have never seen an issue from it. while ((PendingOrders.Count > 0) || (WaitHandle.WaitAny(CommandEventArr) != 1)) { lock (PendingOrders) { if (PendingOrders.Count > 0) { fbo = PendingOrders.Dequeue(); } else { fbo = null; } } // Do Some Work if fbo is != null } Where CommandEventArr is made up of the NewOrderEvent (an auto reset event) and the ExitEvent (a manual reset event). But I just realized today that its not thread safe at all. If this thread gets interrupted right after the first (PendingOrder.Count 0) check has returned false. And then the other thread both enqueues an order and sets the NewOrderEvent before I get a chance to wait on it, the body of the while loop will never run. What's the usual pattern used with a Queue and an AutoResetEvent to fix this and do what I'm trying to do with the code above?

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• [C++] Start a thread using a method pointer

  - by Michael

  Hi ! I'm trying to develop a thread abstraction (POSIX thread and thread from the Windows API), and I would very much like it to be able to start them with a method pointer, and not a function pointer. What I would like to do is an abstraction of thread being a class with a pure virtual method "runThread", which would be implanted in the future threaded class. I don't know yet about the Windows thread, but to start a POSIX thread, you need a function pointer, and not a method pointer. And I can't manage to find a way to associate a method with an instance so it could work as a function. I probably just can't find the keywords (and I've been searching a lot), I think it's pretty much what Boost::Bind() does, so it must exist. Can you help me ?

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• How do I pause main() until all other threads have died?

  - by thechiman

  In my program, I am creating several threads in the main() method. The last line in the main method is a call to System.out.println(), which I don't want to call until all the threads have died. I have tried calling Thread.join() on each thread however that blocks each thread so that they execute sequentially instead of in parallel. Is there a way to block the main() thread until all other threads have finished executing? Here is the relevant part of my code: public static void main(String[] args) { //some other initialization code //Make array of Thread objects Thread[] racecars = new Thread[numberOfRaceCars]; //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racecars[i] = new RaceCar(laps, args[i]); } //Call start() on each Thread for(int i=0; i<numberOfRaceCars; i++) { racecars[i].start(); try { racecars[i].join(); //This is where I tried to using join() //It just blocks all other threads until the current //thread finishes. } catch(InterruptedException e) { e.printStackTrace(); } } //This is the line I want to execute after all other Threads have finished System.out.println("It's Over!"); } Thanks for the help guys! Eric

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• vs2002: c# multi threading question..

  - by dotnet-practitioner

  I would like to invoke heavy duty method dowork on a separate thread and kill it if its taking longer than 3 seconds. Is there any problem with the following code? class Class1 { /// <summary> /// The main entry point for the application. /// </summary> /// [STAThread] static void Main(string[] args) { Console.WriteLine("starting new thread"); Thread t = new Thread(new ThreadStart(dowork)); t.Start(); DateTime start = DateTime.Now; TimeSpan span = DateTime.Now.Subtract(start); bool wait = true; while (wait == true) { if (span.Seconds>3) { t.Abort(); wait = false; } span = DateTime.Now.Subtract(start); } Console.WriteLine("ending new thread after seconds = {0}", span.Seconds); Console.WriteLine("all done"); Console.ReadLine(); } static void dowork() { Console.WriteLine("doing heavy work inside hello"); Thread.Sleep(7000); Console.WriteLine("*** finished**** doing heavy work inside hello"); } }

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• How to call 3 threads sequentially many times?

  - by Hello

  How to call 3 threads sequentially many times? For example: In iteration 1, execution order should be "Thread0-thread1-thread2" then in iteration 2 should be same i.e "Thread0 - thread1-thread2" and so on. The sample code is just executing 3 threads only once. It is not going to 2nd iteration. Thread0 = CreateThread( NULL,0,ThreadProc0, NULL, CREATE_SUSPENDED, &ThreadID); Thread1 = CreateThread( NULL,0,ThreadProc1, NULL, CREATE_SUSPENDED, &ThreadID); Thread2 = CreateThread( NULL,0,ThreadProc2, NULL, CREATE_SUSPENDED, &ThreadID); for(i=0;i<iterations;i++) //Iterations in calling threads { ResumeThread(Thread0); WaitForSingleObject(Thread0, INFINITE); ResumeThread(Thread1); WaitForSingleObject(Thread1, INFINITE); ResumeThread(Thread2); WaitForSingleObject(Thread2, INFINITE); } // Close thread and semaphore handles

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• run two thread at the same time in java

  - by user1805005

  i have used timertask to schedule my java program. now when the run method of timertask is in process, i want to run two threads which run at the same time and do different functions. here is my code.. please help me.. import java.util.Calendar; import java.util.Date; import java.util.Timer; import java.util.TimerTask; public class timercheck extends TimerTask{ // my first thread Thread t1 = new Thread(){ public void run(){ for(int i = 1;i <= 10;i++) { System.out.println(i); } } }; // my second thread Thread t2 = new Thread(){ public void run(){ for(int i = 11;i <= 20;i++) { System.out.println(i); } } }; public static void main(String[] args){ long ONCE_PER_DAY = 1000*60*60*24; Calendar calendar = Calendar.getInstance(); calendar.set(Calendar.HOUR_OF_DAY, 12); calendar.set(Calendar.MINUTE, 05); calendar.set(Calendar.SECOND, 00); Date time = calendar.getTime(); TimerTask check = new timercheck(); Timer timer = new Timer(); timer.scheduleAtFixedRate(check, time ,ONCE_PER_DAY); } @Override // run method of timer task public void run() { t1.start(); t2.start(); } }

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• Is it save to read global data from multiple threads?

  - by user362515

  The scenario is as follows: Create an instance of a class (std::map) and sore it as global variable. Spawn threads. Threads read and use the same global instance of the class All spawned threads quit Global class instance is destroyed No mutex, no thread modifies the global class instance. Is it ok? Thank You

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• Is a Critical Section around an integer getter and setter redundant?

  - by Tim Gradwell

  Do critical sections inside trivial int accessors actually do anything useful? int GetFoo() { CriticalSection(crit_id); return foo; } void SetFoo(int value) { CriticalSection(crit_id); foo = value; } Is it possible for two threads to be attempting to read and write foo simultaneously? I'd have thought 'no' unless integers are written byte-at-a-time, in which case I can see the use. But I'd have though modern cpus would read/write integers in a single atomic action...

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• Iterators over a LInked List in a Game in Java

  - by Matthew

  I am using OpenGl in android and they have a callback method called draw that gets called with out my control. (As fast as the device can handle if I am not mistaken) I have a list of "GameObjects" that have a .draw method and a .update method. I have two different threads that handle each of those. So, the question is, can I declare two different iterators in two different methods in two different threads that iterate over the same Linked List? If so, do I simply declare ListIterator<GameObject> l = objets.listIterator() each time I want a new iterator and it won't interfere with other iterators?

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• Waiting on threads

  - by Paul Reiners

  I have a method that contains the following (Java) code: doSomeThings(); doSomeOtherThings(); doSomeThings() creates some threads, each of which will run for only a finite amount of time. The problem is that I don't want doSomeOtherThings() to be called until all the threads launched by doSomeThings() are finished. (Also doSomeThings() will call methods that may launch new threads and so on. I don't want to execute doSomeOtherThings() until all these threads have finished.) This is because doSomeThings(), among other things will set myObject to null, while doSomeOtherThings() calls myObject.myMethod() and I do not want myObject to be null at that time. Is there some standard way of doing this kind of thing (in Java)?

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• What is the performance cost of calling Thread.isInterupted()?

  - by Michael Barker

  From the java sources, it look like to drops into native code. Is the cost roughly equivalent to a volatile read or does it need to acquire a lock of some type?

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• Why are my thread being terminated ?

  - by Sephy

  Hi, I'm trying to repeat calls to methods through 3 differents threads. But after I start my threads, during the next iteration of my loop, they are all terminated so nothing is executed... The code is as follows : public static void main(String[] args) { main = new Main(); pollingThread.start(); } static Thread pollingThread = new Thread() { @Override public void run() { while (isRunning) { main.poll(); // test the state of the threads try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }; }; public void poll() { if (clientThread == null) { clientThread = new Thread(new Runnable() { @Override public void run() { //create some objects } }); clientThread.start(); } else if (clientThread.isAlive()) { // do some treatment } if (gestionnaireThread == null) { gestionnaireThread = new Thread(new Runnable() { @Override public void run() { //create some objects }; }); gestionnaireThread.start(); } else if (gestionnaireThread.isAlive()) { // do some treatment } if (marchandThread == null) { marchandThread = new Thread(new Runnable() { @Override public void run() { // create some objects }; }); marchandThread.start(); } else if (marchandThread.isAlive()) { // do some treatment } } And for some reason, when I test the state of my different threads, they appear as runnable and then a the 2nd iteration, they are all terminated... What am I doing wrong? I actually have no error, but the threads are terminated and so my loop keeps looping and telling me the threads are terminated.... Thanks for any help.

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• Can two or more threads iterate over the same List<t> without any problems?

  - by CodingCrapper

  Talking about System.Collections.Generic.List here. With example below can Method1 and Method2 execute and the same time, on different threads without any problems? Thanks class Test { private readonly List<MyData> _data; public Test() { _data = LoadData(); } private List<MyData> LoadData() { //Get data from dv. } public void Method1() { foreach (var list in _data) { //do something } } public void Method2() { foreach (var list in _data) { //do something } } }

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• Why does java.util.concurrent.ArrayBlockingQueue use 'while' loops instead of 'if' around calls to

  - by theFunkyEngineer

  I have been playing with my own version of this, using 'if', and all seems to be working fine. Of course this will break down horribly if signalAll() is used instead of signal(), but if only one thread at a time is notified, how can this go wrong? Their code here - check out the put() and take() methods; a simpler and more-to-the-point implementation can be seen at the top of the JavaDoc for Condition. Relevant portion of my implementation below. public Object get() { lock.lock(); try { if( items.size() < 1 ) hasItems.await(); Object poppedValue = items.getLast(); items.removeLast(); hasSpace.signal(); return poppedValue; } catch (InterruptedException e) { e.printStackTrace(); return null; } finally { lock.unlock(); } } public void put(Object item) { lock.lock(); try { if( items.size() >= capacity ) hasSpace.await(); items.addFirst(item); hasItems.signal(); return; } catch (InterruptedException e) { e.printStackTrace(); } finally { lock.unlock(); } } P.S. I know that generally, particularly in lib classes like this, one should let the exceptions percolate up.

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• Multithreaded Applications

  - by j-t-s

  Hi All I have been reading the articles on MSDN, but my mind is dead (this usually happens when I read MSDN (No offense MSDN, but your articles confuse me at times.)), and I'm trying to do some "background work" in may app, but not sure how. It's just a single method. But the application hangs, and I have to wait up to 1 - 3 minutes for it to become ...unhanged? Are there any simple examples that are laying 'roun online somewhere that I can have a look at/play around with? Thank you all

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• Deadlock in c++ on solaris

  - by hitech

  please anybody suggest me how to check the deadlock on solaris with command pstack ? Regards

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• Timer in Java swing

  - by Yesha

  I'm trying to replace Thread.sleep with a java swing timer as I hear that is much better for graphics. Before, I had something set up like this, but it was interfering with the graphics. while(counter < array.size){ Thread.sleep(array.get(counter).startTime); //do first task Thread.sleep(array.get(counter).secondTime); //do second task Thread.sleep(array.get(counter).thirdTime); //do third task counter++ } Now, I'm trying to replace each Thread.sleep with one of these and then I have the actual events that happen after this, but it does not seem to be waiting at all. int test = array.get(counter).time; ActionListener taskPerformer = new ActionListener(){ public void actionPerformed(ActionEvent evt){ } }; Timer t = new Timer(test, taskPerformer); t.setRepeats(false); t.start(); Basically, how do I ensure that the program will wait without giving it any code to execute inside of the timer? Thank you!

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• How do I get a thread safe print in Python 2.6?

  - by knorv

  print in Python is not thread safe according to these articles. A Python 3 work-around is offered in the latter article. How do I get a thread safe print in Python 2.6?

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