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  • Is this BlockingQueue susceptible to deadlock?

    - by unforgiven3
    I've been using this code as a queue that blocks on Dequeue() until an element is enqueued. I've used this code for a few years now in several projects, all with no issues... until now. I'm seeing a deadlock in some code I'm writing now, and in investigating the problem, my 'eye of suspicion' has settled on this BlockingQueue<T>. I can't prove it, so I figured I'd ask some people smarter than me to review it for potential issues. Can you guys see anything that might cause a deadlock in this code? public class BlockingQueue<T> { private readonly Queue<T> _queue; private readonly ManualResetEvent _event; /// <summary> /// Constructor /// </summary> public BlockingQueue() { _queue = new Queue<T>(); _event = new ManualResetEvent(false); } /// <summary> /// Read-only property to get the size of the queue /// </summary> public int Size { get { int count; lock (_queue) { count = _queue.Count; } return count; } } /// <summary> /// Enqueues element on the queue /// </summary> /// <param name="element">Element to enqueue</param> public void Enqueue(T element) { lock (_queue) { _queue.Enqueue(element); _event.Set(); } } /// <summary> /// Dequeues an element from the queue /// </summary> /// <returns>Dequeued element</returns> public T Dequeue() { T element; while (true) { if (Size == 0) { _event.Reset(); _event.WaitOne(); } lock (_queue) { if (_queue.Count == 0) continue; element = _queue.Dequeue(); break; } } return element; } /// <summary> /// Clears the queue /// </summary> public void Clear() { lock (_queue) { _queue.Clear(); } } }

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  • How can one manage to fully use the newly enhanced Parallelism features in .NET 4.0?

    - by Will Marcouiller
    I am pretty much interested into using the newly enhanced Parallelism features in .NET 4.0. I have also seen some possibilities of using it in F#, as much as in C#. Despite, I can only see what PLINQ has to offer with, for example, the following: var query = from c in Customers.AsParallel() where (c.Name.Contains("customerNameLike") select c; There must for sure be some other use of this parallelism thing. Have you any other examples of using it? Is this particularly turned toward PLINQ, or are there other usage as easy as PLINQ? Thanks! =)

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  • How to correctly stop thread which is using Control.Invoke

    - by codymanix
    I tried the following (pseudocode) but I always get a deadlock when Iam trying to stop my thread. The problem is that Join() waits for the thread to complete and a pending Invoke() operation is also waiting to complete. How can I solve this? Thread workerThread = new Thread(BackupThreadRunner); volatile bool cancel; // this is the thread worker routine void BackupThreadRunner() { while (!cancel) { DoStuff(); ReportProgress(); } } // main thread void ReportProgress() { if (InvokeRequired) { Invoke(ReportProgress); } UpdateStatusBarAndStuff(); } // main thread void DoCancel() { cancel=true; workerThread.Join(); }

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  • What is the JVM Scheduling algorithm ?

    - by IHawk
    Hello ! I am really curious about how does the JVM work with threads ! In my searches in internet, I found some material about RTSJ, but I don't know if it's the right directions for my answers. I also found this topic in sun's forums, http://forums.sun.com/thread.jspa?forumID=513&threadID=472453, but that's not satisfatory. Can someone give me some directions, material, articles or suggestion about the JVM scheduling algorithm ? I am also looking for information about the default configurations of Java threads in the scheduler, like 'how long does it take for every thread' in case of time-slicing. And this stuff. I would appreciate any help ! Thank you !

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  • Does UIActivityIndicator require manual threading on iPhone

    - by Akusete
    I am running creating an iPhone application which performs a costly operation and I wanted to create an activityIndicator to let the user know the application has not frozen. The operation is performed entirely in one event call... so there is no chance for the UI framework to receive control to actually display and animate this indicator. The sample apps which use the UIActivityIndicator (or any other similar animation) start and stop the animation in different events, triggered separately at different stages of the program. Do I need to manually create a separate thread to run my operation in, or is there already default support for this kind of behavior?

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  • passing pipe to threads

    - by alaamh
    I see it's easy to open pipe between two process using fork, but how we can passing open pipe to threads. Assume we need to pass out of PROGRAM A to PROGRAM B "may by more than one thread", PROGRAM B send his output to PROGRAM C #include <stdio.h> #include <stdlib.h> #include <pthread.h> struct targ_s { int fd_reader; }; void *thread1(void *arg) { struct targ_s *targ = (struct targ_s*) arg; int status, fd[2]; pid_t pid; pipe(fd); pid = fork(); if (pid == 0) { dup2(STDIN_FILENO, targ->fd_reader); close(fd[0]); dup2(fd[1], STDOUT_FILENO); close(fd[1]); execvp ("PROGRAM B", NULL); exit(1); } else { close(fd[1]); dup2(fd[0], STDIN_FILENO); close(fd[0]); execl("PROGRAM C", NULL); wait(&status); return NULL; } } int main(void) { FILE *fpipe; char *command = "PROGRAM A"; char buffer[1024]; if (!(fpipe = (FILE*) popen(command, "r"))) { perror("Problems with pipe"); exit(1); } char* outfile = "out.dat"; FILE* f = fopen (outfile, "wb"); int fd = fileno( f ); struct targ_s targ; targ.fd_reader = fd; pthread_t thid; if (pthread_create(&thid, NULL, thread1, &targ) != 0) { perror("pthread_create() error"); exit(1); } int len; while (read(fpipe, buffer, sizeof (buffer)) != 0) { len = strlen(buffer); write(fd, buffer, len); } pclose(fpipe); return (0); }

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  • How to automatically run in the background?

    - by Hun1Ahpu
    I'm not sure that it's not implemented yet, I hope that it is. But I know that in .Net programmers should manually run time-consuming task in the background thread. So every time we handle some UI event and we understand that this will take some time we also understand that this will hang UI thread and our application. And then we make all this Background work things and handle callbacks or whatever. So my question is: Is there in some language/platform a mechanism that will automatically run time-consuming tasks in the background and will do all related work itself? So we just write the code for handling specific UI event and this code will be somehow detected as time-consuming and will be executed in background. And if there isn't, then why?

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  • How would you implement this "WorkerChain" functionality in .NET?

    - by Dan Tao
    Sorry for the vague question title -- not sure how to encapsulate what I'm asking below succinctly. (If someone with editing privileges can think of a more descriptive title, feel free to change it.) The behavior I need is this. I am envisioning a worker class that accepts a single delegate task in its constructor (for simplicity, I would make it immutable -- no more tasks can be added after instantiation). I'll call this task T. The class should have a simple method, something like GetToWork, that will exhibit this behavior: If the worker is not currently running T, then it will start doing so right now. If the worker is currently running T, then once it is finished, it will start T again immediately. GetToWork can be called any number of times while the worker is running T; the simple rule is that, during any execution of T, if GetToWork was called at least once, T will run again upon completion (and then if GetToWork is called while T is running that time, it will repeat itself again, etc.). Now, this is pretty straightforward with a boolean switch. But this class needs to be thread-safe, by which I mean, steps 1 and 2 above need to comprise atomic operations (at least I think they do). There is an added layer of complexity. I have need of a "worker chain" class that will consist of many of these workers linked together. As soon as the first worker completes, it essentially calls GetToWork on the worker after it; meanwhile, if its own GetToWork has been called, it restarts itself as well. Logically calling GetToWork on the chain is essentially the same as calling GetToWork on the first worker in the chain (I would fully intend that the chain's workers not be publicly accessible). One way to imagine how this hypothetical "worker chain" would behave is by comparing it to a team in a relay race. Suppose there are four runners, W1 through W4, and let the chain be called C. If I call C.StartWork(), what should happen is this: If W1 is at his starting point (i.e., doing nothing), he will start running towards W2. If W1 is already running towards W2 (i.e., executing his task), then once he reaches W2, he will signal to W2 to get started, immediately return to his starting point and, since StartWork has been called, start running towards W2 again. When W1 reaches W2's starting point, he'll immediately return to his own starting point. If W2 is just sitting around, he'll start running immediately towards W3. If W2 is already off running towards W3, then W2 will simply go again once he's reached W3 and returned to his starting point. The above is probably a little convoluted and written out poorly. But hopefully you get the basic idea. Obviously, these workers will be running on their own threads. Also, I guess it's possible this functionality already exists somewhere? If that's the case, definitely let me know!

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  • Limiting the number of threads executing a method at a single time.

    - by Steve_
    We have a situation where we want to limit the number of paralell requests our application can make to its application server. We have potentially 100+ background threads running that will want to at some point make a call to the application server but only want 5 threads to be able to call SendMessage() (or whatever the method will be) at any one time. What is the best way of achieving this? I have considered using some sort of gatekeeper object that blocks threads coming into the method until the number of threads executing in it has dropped below the threshold. Would this be a reasonable solution or am I overlooking the fact that this might be dirty/dangerous? We are developing in C#.NET 3.5. Thanks, Steve

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  • Issue with Java join() method.

    - by gmunk
    First of all here are some code snippets: http://pastebin.com/9ZCwekXs http://pastebin.com/TtLLXPYP I'm trying to animate some images. The thing is that I want the main thread to wait for the animation thread to finish and then to continue. I searched around, read a little bit and decided to use the join() method. It perfectly waits for the thread to finish but I doesn't animate correctly. The repaint() method gets called 2 times instead of nine. I think maybe the problem is because I used singletons. Here is the singleton implementation. http://pastebin.com/bA3qLZJE

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  • iPhone: One Object, One Thread

    - by GingerBreadMane
    On the iPhone, I would like to do some operations on an image in a separate thread. Rather than dealing with semiphores, locking, etc., I'd like to use the 'One Object, One Thread' method of safely writing this concurrent operation. I'm not sure what is the correct way to copy my object into a new thread so that the object is not accessed in the main thread. Do I use the 'copy' method? If so, do I do this before the thread or inside the thread? ... -(void)someMethod{ UIImage *myImage; [NSThread detachNewThreadSelector:@selector(getRotatedImage:) toTarget:self withObject:myImage]; } -(void)getRotatedImage:(UIImage *)image{ ... ... UIImage *copiedImage = [image copy]; ... ... }

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  • ReaderWriterLockSlim and Pulse/Wait

    - by Jono
    Is there an equivalent of Monitor.Pulse and Monitor.Wait that I can use in conjunction with a ReaderWriterLockSlim? I have a class where I've encapsulated multi-threaded access to an underlying queue. To enqueue something, I acquire a lock that protects the underlying queue (and a couple of other objects) then add the item and Monitor.Pulse the locked object to signal that something was added to the queue. public void Enqueue(ITask task) { lock (mutex) { underlying.Enqueue(task); Monitor.Pulse(mutex); } } On the other end of the queue, I have a single background thread that continuously processes messages as they arrive on the queue. It uses Monitor.Wait when there are no items in the queue, to avoid unnecessary polling. (I consider this to be good design, but any flames (within reason) are welcome if they help me learn otherwise.) private void DequeueForProcessing(object state) { while (true) { ITask task; lock (mutex) { while (underlying.Count == 0) { Monitor.Wait(mutex); } task = underlying.Dequeue(); } Process(task); } } As more operations are added to this class (requiring read-only access to the lock protected underlying), someone suggested using ReaderWriterLockSlim. I've never used the class before, and assuming it can offer some performance benefit, I'm not against it, but only if I can keep the Pulse/Wait design.

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  • Returning from method inside a @synchronized block

    - by Michael Waterfall
    I'd just like to know if it's advised to return from a method within a @synchronized block? For example: - (id)test { @synchronized(self) { if (a) return @"A"; else return @"B"; } } As opposed to: - (id)test { NSString *value; @synchronized(self) { if (a) value = @"A"; else value = @"B"; } return value; } This sample is rather simplistic, but sometimes in a complex method it would make things simpler to be able to return from within a @synchronized block.

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  • Parallel Task In C#.net

    - by Test123
    I have C#.net application. I wanted to run my application In Thread. But because of third party dll it dont allow to use application in multiThread. There is one object in thrid party dll ,which only allow to create instance at one time only. When i manually run application exe instnace multiple time & process my data it process successfully..(might because of each exe run with its application domain) Same thing i require to implement from C# code. for that i have created dll which can accessible by Type.GetTypeFromProgID()..but multiple dll instnace creating same problem. Is there any way i could achive manual parallelism through code to process same exe code in multiple application domain?

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  • java methods and race condition in a jsp/servlets application.

    - by A.S al-shammari
    Hi. Suppose that I have a method called doSomething() and I want to use this method in a multithreaded application (each servlet inherits from HttpServlet).I'm wondering if it is possible that a race condition will occur in the following cases: doSomething() is not staic method and it writes values to a database. doSomething() is static method but it does not write values to a database. what I have noticed that many methods in my application may lead to a race condition or dirty read/write. for example , I have a Poll System , and for each voting operation, a certain method will change a single cell value for that poll as the following: [poll_id | poll_data ] [1 | {choice_1 : 10, choice_2 : 20}] will the JSP/Servlets app solve these issues by itself, or I have to solve all that by myself? Thanks..

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  • If I allocate memory in one thread in C++ can I de-allocate it in another

    - by Shane MacLaughlin
    If I allocate memory in one thread in C++ (either new or malloc) can I de-allocate it in another, or must both occur in the same thread? Ideally, I'd like to avoid this in the first place, but I'm curious to know is it legal, illegal or implementation dependent. Edit: The compilers I'm currently using include VS2003, VS2008 and Embedded C++ 4.0, targetting XP, Vista, Windows 7 and various flavours of Windows CE / PocketPC & Mobile. So basically all Microsoft but across an array of esoteric platforms.

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  • Running code when all threads are finished processing.

    - by rich97
    Quick note: Java and Android noob here, I'm open to you telling me I'm stupid (as long as you tell me why.) I have an android application which requires me start multiple threads originating from various classes and only advance to the next activity once all threads have done their job. I also want to add a "failsafe" timeout in case one the the threads takes too long (HTTP request taking too long or something.) I searched Stack Overflow and found a post saying that I should create a class to keep a running total of open threads and then use a timer to poll for when all the threads are completed. I think I've created a working class to do this for me, it's untested as of yet but has no errors showing in eclipse. Is this a correct implementation? Are there any APIs that I should be made aware of (such as classes in the Java or Android APIs that could be used in place of the abstract classes at the bottom of the class?) package com.dmp.geofix.libs; import java.util.ArrayList; import java.util.Iterator; import java.util.Timer; import java.util.TimerTask; public class ThreadMonitor { private Timer timer = null; private TimerTask timerTask = null; private OnSuccess onSuccess = null; private OnError onError = null; private static ArrayList<Thread> threads; private final int POLL_OPEN_THREADS = 100; private final int TIMEOUT = 10000; public ThreadMonitor() { timerTask = new PollThreadsTask(); } public ThreadMonitor(OnSuccess s) { timerTask = new PollThreadsTask(); onSuccess = s; } public ThreadMonitor(OnError e) { timerTask = new PollThreadsTask(); onError = e; } public ThreadMonitor(OnSuccess s, OnError e) { timerTask = new PollThreadsTask(); onSuccess = s; onError = e; } public void start() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().start(); } timer = new Timer(); timer.schedule(timerTask, 0, POLL_OPEN_THREADS); } public void finish() { Iterator<Thread> i = threads.iterator(); while (i.hasNext()) { i.next().interrupt(); } threads.clear(); timer.cancel(); } public void addThread(Thread t) { threads.add(t); } public void removeThread(Thread t) { threads.remove(t); t.interrupt(); } class PollThreadsTask extends TimerTask { private int timeElapsed = 0; @Override public void run() { timeElapsed += POLL_OPEN_THREADS; if (timeElapsed <= TIMEOUT) { if (threads.isEmpty() == false) { if (onSuccess != null) { onSuccess.run(); } } } else { if (onError != null) { onError.run(); } finish(); } } } public abstract class OnSuccess { public abstract void run(); } public abstract class OnError { public abstract void run(); } }

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  • Java threads, wait time always 00:00:00-Producer/Consumer

    - by user3742254
    I am currently doing a producer consumer problem with a number of threads and have had to set priorities and waits to them to ensure that one thread, the security thread, runs last. I have managed to do this and I have managed to get the buffer working. The last thing that I am required to do is to show the wait time of threads that are too large for the buffer and to calculate the average wait time. I have included code to do so, but everything I run the program, the wait time is always returned as 00:00:00, and by extension, the average is returned as the same. I was speaking to one of my colleagues who said that it is not a matter of the code but rather a matter of the computer needing to work off of one processor, which can be adjusted in the task manager settings. He has an HP like myself but his program prints the wait time 180 times, whereas mine prints usually about 3-7 times and is only 00:00:01 on one instance before finishing when I have made the processor adjustments. My other colleague has an iMac and hers puts out an average of 42:00:34(42 minutes??) I am very confused about this because I can see no difference between our codes and like my colleague said, I was wondering is it a computer issue. I am obviously concerned as I wanted to make sure that my code correctly calculated an average wait time, but that is impossible to tell when the wait times always show as 00:00:00. To calculate the thread duration, including the time it entered and exited the buffer was done by using a timestamp import, and then subtracting start time from end time. Is my code correct for this issue or is there something which is missing? I would be very grateful for any solutions. Below is my code: My buffer class package com.Com813cw; import java.text.DateFormat; import java.text.SimpleDateFormat; /** * Created by Rory on 10/08/2014. */ class Buffer { private int contents, count = 0, process = 200; private int totalRam = 1000; private boolean available = false; private long start, end, wait, request = 0; private DateFormat time = new SimpleDateFormat("ss:SSS"); public int avWaitTime =0; public void average(){ System.out.println("Average Application Request wait time: "+ time.format(request/count)); } public synchronized int get() { while (process <= 500) { try { wait(); } catch (InterruptedException e) { } } process -= 200; System.out.println("CPU After Process " + process); notifyAll(); return contents; } public synchronized void put(int value) { if (process <= 500) { process += value; } else { start = System.currentTimeMillis(); try { wait(); } catch (InterruptedException e) { } end = System.currentTimeMillis(); wait = end - start; count++; request += wait; System.out.println("Application Request Wait Time: " + time.format(wait)); process += value; contents = value; calcWait(wait, count); } notifyAll(); } public void calcWait(long wait, int count){ this.avWaitTime = (int) (wait/count); } public void printWait(){ System.out.println("Wait time is " + time.format(this.avWaitTime)); } } My spotify class package com.Com813cw; import java.sql.Timestamp; /** * Created by Rory on 11/08/2014. */ class Spotify extends Thread { private Buffer buffer; private int number; private int bytes = 250; public Spotify(Buffer c, int number) { buffer = c; this.number = number; } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 20; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes "); try { sleep(1000); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("Spotify has finished executing."); System.out.println("Time taken to execute was " + timeTaken + " milliseconds"); System.out.println("Time that Spotify thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("-----------------------------"); } } My BubbleWitch class package com.Com813cw; import java.lang.*; import java.lang.System; import java.sql.Timestamp; /** * Created by Rory on 10/08/2014. */ class BubbleWitch2 extends Thread { private Buffer buffer; private int number; private int bytes = 100; public BubbleWitch2(Buffer c, int number) { buffer = c; this.number=number ; } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 10; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes "); try { sleep(1000); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("BubbleWitch2 has finished executing."); System.out.println("Time taken to execute was " +timeTaken+ " milliseconds"); System.out.println("Time Bubblewitch2 thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("-----------------------------"); } } My Test class package com.Com813cw; /** * Created by Rory on 10/08/2014. */ public class ProducerConsumerTest { public static void main(String[] args) throws InterruptedException { Buffer c = new Buffer(); BubbleWitch2 p1 = new BubbleWitch2(c,1); Processor c1 = new Processor(c, 1); Spotify p2 = new Spotify(c, 2); SystemManagement p3 = new SystemManagement(c, 3); SecurityUpdate p4 = new SecurityUpdate(c, 4, p1, p2, p3); p1.setName("BubbleWitch2 "); p2.setName("Spotify "); p3.setName("System Management "); p4.setName("Security Update "); p1.setPriority(10); p2.setPriority(10); p3.setPriority(10); p4.setPriority(5); c1.start(); p1.start(); p2.start(); p3.start(); p4.start(); p2.join(); p3.join(); p4.join(); c.average(); System.exit(0); } } My security update package com.Com813cw; import java.lang.*; import java.lang.System; import java.sql.Timestamp; /** * Created by Rory on 11/08/2014. */ class SecurityUpdate extends Thread { private Buffer buffer; private int number; private int bytes = 150; private int process = 0; public SecurityUpdate(Buffer c, int number, BubbleWitch2 bubbleWitch2, Spotify spotify, SystemManagement systemManagement) throws InterruptedException { buffer = c; this.number = number; bubbleWitch2.join(); spotify.join(); systemManagement.join(); } long startTime = System.currentTimeMillis(); public void run() { for (int i = 0; i < 15; i++) { buffer.put(bytes); System.out.println(getName() + this.number + " put: " + bytes + " bytes"); try { sleep(1500); } catch (InterruptedException e) { } } long endTime = System.currentTimeMillis(); long timeTaken = endTime - startTime; java.util.Date date = new java.util.Date(); System.out.println("-----------------------------"); System.out.println("Security Update has finished executing."); System.out.println("Time taken to execute was " + timeTaken + " milliseconds"); System.out.println("Time that SecurityUpdate thread exited Buffer was " + new Timestamp(date.getTime())); System.out.println("------------------------------"); } } I'd be grateful as I said for any help as this is the last and most frustrating obstacle.

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  • How to manage db connections on server?

    - by simpatico
    I have a severe problem with my database connection in my web application. Since I use a single database connection for the whole application from singleton Database class, if i try concurrent db operations (two users) the database rollsback the transactions. This is my static method used: All threads/servlets call static Database.doSomething(...) methods, which in turn call the the below method. private static /* synchronized*/ Connection getConnection(final boolean autoCommit) throws SQLException { if (con == null) { con = new MyRegistrationBean().getConnection(); } con.setAutoCommit(true); //TODO return con; } What's the recommended way to manage this db connection/s I have, so that I don't incurr in the same problem.

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