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• BlockingQueue decorator that logs removed objects

  - by scompt.com

  I have a BlockingQueue that's being used in a producer-consumer situation. I would like to decorate this queue so that every object that's taken from it is logged. I know what the straightforward implementation would look like: simply implement BlockingQueue and accept a BlockingQueue in the constructor to which all of the methods would delegate. Is there another way that I'm missing? A library perhaps? Something with a callback interface?

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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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• Two BlockingQueue in the same endless loop?

  - by DrDol

  I have a thread, that processes incomming messages (endless loop). For this, I use a BlockingQueue (Java), which works as quite nice. Now, I want to add a second processor in the same Class oder method. The problem now is, that in the endless loop i have this part newIncomming = this.incommingProcessing.take(); This part blocks if the Queue is empty. I'm looking for a solution to process to queues in the same class. The second queue can only processed, it some data is coming in for the first Queue. Is there a way to handle tow blocking queues in the same endless loop?

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• C# Is it possible to interrupt a specific thread inside a ThreadPool?

  - by Lirik

  Suppose that I've queued a work item in a ThreadPool, but the work item blocks if there is no data to process (reading from a BlockingQueue). If the queue is empty and there will be no more work going into the queue, then I must call the Thread.Interrupt method if I want to interrupt the blocking task, but how does one do the same thing with a ThreadPool? The code might look like this: void Run() { try { while(true) { blockingQueue.Dequeue(); doSomething(); } } finally { countDownLatch.Signal(); } } I'm aware that the best thing to do in this situation is use a regular Thread, but I'm wondering if there is a ThreadPool equivalent way to interrupt a work item.

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• Is nested synchronized block necessary?

  - by Dan

  I am writing a multithreaded program and I have a method that has a nested synchronized blocks and I was wondering if I need the inner sync or if just the outer sync is good enough. public class Tester { private BlockingQueue<Ticket> q = new LinkedBlockingQueue<>(); private ArrayList<Long> list = new ArrayList<>(); public void acceptTicket(Ticket p) { try { synchronized (q) { q.put(p); synchronized (list) { if (list.size() < 5) { list.add(p.getSize()); } else { list.remove(0); list.add(p.getSize()); } } } } catch (InterruptedException ex) { Logger.getLogger(Consumer.class.getName()).log(Level.SEVERE, null, ex); } } } EDIT: This isn't a complete class as I am still working on it. But essentially I am trying to emulate a ticket machine. The ticket machine maintains a list of tickets in the BlockingQueue q. Whenever a client adds a ticket to the machine, the machine also keeps track of the price of the last 5 tickets (ArrayList list)

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• Communication between Box2D and libGDX Stage (Scene2D) running in separate threads

  - by atok

  I'm making a physics based 2D game using libGDX and Box2D. I want to move the execution of the simulation out of render thread. I use immutable messages and the BlockingQueue to pass the information about player actions. The Box2D applies forces and runs a frame of simulation. In the next step I would like to sync back the changes and update Scene2D Actors accordingly. Making an immutable copy of the state of the game world and sending it back using Gdx.app.postRunnable() is one option but it seems inefficient. Is there any other option?

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• Logic for controll concurrent in block or funciton

  - by Hlex

  1)My environment is web application, I accept large request from selvets. A) In some block/method i want to control concurrent to not greater than 5 B) if there are 5 request in that block , the new coming must wait up to 60 second then throws error C) if there are sleep/waiting request most then 30,throws error How I do this? 2)(Optional Question) from above I have to distribute control logic to all clustered host. I plan to use hazelcast to share the control logic (e.g. current counter) I see they provide BlockingQueue & ExectorService but I have no idea how to use in my case. Please recommend if you have idea.

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• Logic for controll concurrent in block/method

  - by Hlex

  1)My environment is web application, I develop servlet to receive request. A) In some block/method i want to control concurrent to not greater than 5 B) if there are 5 request in that block , the new coming must wait up to 60 second then throws error C) if there are sleep/waiting request more then 30, the 31th request will be throwed an error How I do this? 2)(Optional Question) from above I have to distribute control logic to all clustered host. I plan to use hazelcast to share the control logic (e.g. current counter) I see they provide BlockingQueue & ExectorService but I have no idea how to use in my case. Please recommend if you have idea.

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• For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue?

  - by Jonathan Allen

  For single-producer, single-consumer should I use a BlockingCollection or a ConcurrentQueue? Concerns: * My goal is to pull up to 100 items at a time and send them as a batch to the next step. * If I use a ConcurrentQueue, I have to manually cause it to go asleep when there is no work to be done. Otherwise I waste CPU cycles on spinning. * If I use a BlockingQueue and I only have 99 work items, it could indefinitely block until there the 100th item arrives. http://msdn.microsoft.com/en-us/library/system.collections.concurrent.aspx

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• Using thread inter-communication to increase my server app's IO throughput; not sure how

  - by Howard Guo

  My server application creates a new thread for each incoming connection. Incoming requests are serialized in a BlockingQueue. There is one worker thread taking items from the queue, produce a response and send the response through socket. I have noticed a throughput issue: Currently, worker thread is responsible of sending the response message through socket, thus severely wasting processing power and throughput. I am considering: rather than sending the response itself, why not telling network IO threads to send the response? However, when I think about thread inter-communication, I cannot yet figure out how to approach it: Worker thread will produce a response, but how will it inform the response message to IO thread? Is there a standard/best practice? Thank you.

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• How to make Stack.Pop threadsafe

  - by user260197

  I am using the BlockingQueue code posted in this question, but realized I needed to use a Stack instead of a Queue given how my program runs. I converted it to use a Stack and renamed the class as needed. For performance I removed locking in Push, since my producer code is single threaded. My problem is how can thread working on the (now) thread safe Stack know when it is empty. Even if I add another thread safe wrapper around Count that locks on the underlying collection like Push and Pop do, I still run into the race condition that access Count and then Pop are not atomic. Possible solutions as I see them (which is preferred and am I missing any that would work better?): Consumer threads catch the InvalidOperationException thrown by Pop(). Pop() return a nullptr when _stack-Count == 0, however C++-CLI does not have the default() operator ala C#. Pop() returns a boolean and uses an output parameter to return the popped element. Here is the code I am using right now: generic <typename T> public ref class ThreadSafeStack { public: ThreadSafeStack() { _stack = gcnew Collections::Generic::Stack<T>(); } public: void Push(T element) { _stack->Push(element); } T Pop(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Pop(); } finally { System::Threading::Monitor::Exit(_stack); } } public: property int Count { int get(void) { System::Threading::Monitor::Enter(_stack); try { return _stack->Count; } finally { System::Threading::Monitor::Exit(_stack); } } } private: Collections::Generic::Stack<T> ^_stack; };

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• Android Signal 11 (SIGSEGV)

  - by Naturjoghurt

  I read many posts here and on other sites, but can not find the problem creating my Error: I use an AsyncTask because I want to easily manipulate the UI Thread before and after Execution. In doInBackground I create a ThreadPoolExecutor and execute Runnables. If I only execute 1 Runnable with the Executor, there is no Problem, but if I execute another Runnable I get following Error: 06-26 18:00:42.288: A/libc(25073): Fatal signal 11 (SIGSEGV) at 0x7f486162 (code=1), thread 25106 (pool-1-thread-2) 06-26 18:00:42.304: D/dalvikvm(25073): GC_CONCURRENT freed 119K, 2% free 8908K/9056K, paused 4ms+4ms, total 45ms 06-26 18:00:42.327: I/System.out(25073): In Check All with Prefix: a and Length: 4 06-26 18:00:42.390: I/DEBUG(126): *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** 06-26 18:00:42.390: I/DEBUG(126): Build fingerprint: 'google/yakju/maguro:4.2.2/JDQ39/573038:user/release-keys' 06-26 18:00:42.390: I/DEBUG(126): Revision: '9' 06-26 18:00:42.390: I/DEBUG(126): pid: 25073, tid: 25106, name: pool-1-thread-2 >>> de.uni_duesseldorf.cn.distributed_computing2 <<< 06-26 18:00:42.390: I/DEBUG(126): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 7f486162 ... 06-26 18:00:42.538: I/DEBUG(126): memory map around fault addr 7f486162: 06-26 18:00:42.538: I/DEBUG(126): 60292000-60391000 06-26 18:00:42.538: I/DEBUG(126): (no map for address) 06-26 18:00:42.538: I/DEBUG(126): bed14000-bed35000 [stack] I set up the ThreadPoolExecutor like this: // numberOfPackages: Number of Runnables to be executed public void initializeThreadPoolExecutor (int numberOfPackages) { int corePoolSize = Runtime.getRuntime().availableProcessors(); int maxPoolSize = numberOfPackages; long keepAliveTime = 60; final BlockingQueue workingQueue = new LinkedBlockingQueue(); executor = new ThreadPoolExecutor(corePoolSize, maxPoolSize, keepAliveTime, TimeUnit.SECONDS, workingQueue); } I have no clue, why it fails when starting the second Thread. Maybe Memory Leaks? Any Help appreciated. Thanks in Advance

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