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Search found 813 results on 33 pages for 'concurrency'.

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• Best way to reuse a Runnable

  - by Gandalf

  I have a class that implements Runnable and am currently using an Executor as my thread pool to run tasks (indexing documents into Lucene). executor.execute(new LuceneDocIndexer(doc, writer)); My issue is that my Runnable class creates many Lucene Field objects and I would rather reuse them then create new ones every call. What's the best way to reuse these objects (Field objects are not thread safe so I cannot simple make them static) - should I create my own ThreadFactory? I notice that after a while the program starts to degrade drastically and the only thing I can think of is it's GC overhead. I am currently trying to profile the project to be sure this is even an issue - but for now lets just assume it is.

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• Do the 'up to date' guarantees provided by final field in Java's memory model extend to indirect ref

  - by mattbh

  The Java language spec defines semantics of final fields in section 17.5: The usage model for final fields is a simple one. Set the final fields for an object in that object's constructor. Do not write a reference to the object being constructed in a place where another thread can see it before the object's constructor is finished. If this is followed, then when the object is seen by another thread, that thread will always see the correctly constructed version of that object's final fields. It will also see versions of any object or array referenced by those final fields that are at least as up-to-date as the final fields are. My question is - does the 'up-to-date' guarantee extend to the contents of nested arrays, and nested objects? An example scenario: Thread A constructs a HashMap of ArrayLists, then assigns the HashMap to final field 'myFinal' in an instance of class 'MyClass' Thread B sees a (non-synchronized) reference to the MyClass instance and reads 'myFinal', and accesses and reads the contents of one of the ArrayLists In this scenario, are the members of the ArrayList as seen by Thread B guaranteed to be at least as up to date as they were when MyClass's constructor completed?

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• Find messages from certain key till certain key while being able to remove stale keys.

  - by Alfred

  My problem Let's say I add messages to some sort of datastructure: 1. "dude" 2. "where" 3. "is" 4. "my" 5. "car" Asking for messages from index[4,5] should return: "my","car". Next let's assume that after a while I would like to purge old messages because they aren't useful anymore and I want to save memory. Let's say at time x messages[1-3] became stale. I assume that it would be most efficient to just do the deletion once every x seconds. Next my datastructure should contain: 4. "my" 5. "car" My solution? I was thinking of using a concurrentskiplistset or concurrentskiplist map. Also I was thinking of deleting the old messages from inside a newSingleThreadScheduledExecutor. I would like to know how you would implement(efficiently/thread-safe) this or maybe use a library?

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• re: adding more threads to forkjoinpool

  - by paintcan

  Word up y'all I recently successfully experimented with Scala futures, got future { my shiznit } all over da place. I'm pleased as punch w/ the gains I'm seeing from the parallelism and whatnot, but I'm only seeing 4 worker threads. Wanna see some more. I've been looking all over for how I can crank up the number of threads to 11, but no luck. Help me out doods

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• C++: is it safe to read an integer variable that's being concurrently modified without locking?

  - by Hongli

  Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect reads too? I've heard that there are some hardware architectures on which, if one thread modifies a variable, and another thread reads it, then the read result will be garbage; in this case I do need to protect reads. I've never seen such architectures though. This question assumes that a single transaction only consists of updating a single integer variable so I'm not worried about the states of any other variables that might also be involved in a transaction.

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• How do I ensure data consistency in this concurrent situation?

  - by MalcomTucker

  The problem is this: I have multiple competing threads (100+) that need to access one database table Each thread will pass a String name - where that name exists in the table, the database should return the id for the row, where the name doesn't already exist, the name should be inserted and the id returned. There can only ever be one instance of name in the database - ie. name must be unique How do I ensure that thread one doesn't insert name1 at the same time as thread two also tries to insert name1? In other words, how do I guarantee the uniqueness of name in a concurrent environment? This also needs to be as efficient as possible - this has the potential to be a serious bottleneck. I am using MySQL and Java. Thanks

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• What are Erlang processes behind the scenes?

  - by Roger Alsing

  I've got very limited knowledge about Erlang, but as far as I understand, it can spawn "processes" with a very low cost. So I wonder, what are those "processes" behind the scenes? Are they Fibers? Threads? Continuations?

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• strange bug - how to pause a java program?

  - by TerraNova993

  I'm trying to: display a text in a jLabel, wait for two seconds, then write a new text in the jLabel this should be simple, but I get a strange bug: the first text is never written, the application just waits for 2 seconds and then displays the final text. here is the example code: private void testButtonActionPerformed(java.awt.event.ActionEvent evt) { displayLabel.setText("Clicked!"); // first method with System timer /* long t0= System.currentTimeMillis(); long t1= System.currentTimeMillis(); do{ t1 = System.currentTimeMillis(); } while ((t1 - t0) < (2000)); */ // second method with thread.sleep() try { Thread.currentThread().sleep(2000); } catch (InterruptedException e) {} displayLabel.setText("STOP"); } with this code, the text "Clicked!" is never displayed. I just get a 2 seconds - pause and then the "STOP" text. I tried to use System timer with a loop, or Thread.sleep(), but both methods give the same result.

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• What is the absolute fastest way to implement a concurrent queue with ONLY one consumer and one producer?

  - by JohnPristine

  java.util.concurrent.ConcurrentLinkedQueue comes to mind, but is it really optimum for this two-thread scenario? I am looking for the minimum latency possible on both sides (producer and consumer). If the queue is empty you can immediately return null AND if the queue is full you can immediately discard the entry you are offering. Does ConcurrentLinkedQueue use super fast and light locks (AtomicBoolean) ? Has anyone benchmarked ConcurrentLinkedQueue or knows about the ultimate fastest way of doing that? Additional Details: I imagine the queue should be a fair one, meaning the consumer should not make the consumer wait any longer than it needs (by front-running it) and vice-versa.

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• Tomcat thread waiting on and locking the same resource

  - by Adam Matan

  Consider the following Java\Tomcat thread dump: "http-0.0.0.0-4080-4" daemon prio=10 tid=0x0000000019a2b000 nid=0x360e in Object.wait() [0x0000000040b71000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x00002ab5565fe358> (a org.apache.tomcat.util.net.JIoEndpoint$Worker) at java.lang.Object.wait(Object.java:485) at org.apache.tomcat.util.net.JIoEndpoint$Worker.await(JIoEndpoint.java:458) - locked <0x00002ab5565fe358> (a org.apache.tomcat.util.net.JIoEndpoint$Worker) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:484) at java.lang.Thread.run(Thread.java:662) Is this a deadlock? It seems that the same resource (0x00002ab5565fe358) is both locked and waited on - what does it mean?

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• Is this technically thread safe despite being mutable?

  - by Finbarr

  Yes, the private member variable bar should be final right? But actually, in this instance, it is an atomic operation to simply read the value of an int. So is this technically thread safe? class foo { private int bar; public foo(int bar) { this.bar = bar; } public int getBar() { return bar; } } // assume infinite number of threads repeatedly calling getBar on the same instance of foo.

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• Spring.Net how does WebApplicationContext.GetObject handle concurrent requests?

  - by Alfamale

  Apologies if I have missed something obvious here but having gone through the documentation, forums and googled for a number of hours, I just can't find a definitive answer to the following questions: How does the WebApplicationContext.GetObject() method handle concurrent requests? Are the requests serialized or executed in parallel? Is there any performance data available to demonstrate how it behaves under load? Thanks in advance for your help, Andrew

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• EJB container managed threading model

  - by sof

  Any good source/links or concise explaination about it? Thanks a lot!

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• How to debug ConcurrentModificationException?

  - by Dani

  I encountered ConcurrentModificationException and by looking at it I can't see the reason why it's happening; the area throwing the exception and all the places modifying the collection are surrounded by synchronized (this.locks.get(id)) { ... } // locks is a HashMap<String, Object>; I tried to catch the the pesky thread but all I could nail (by setting a breakpoint in the exception) is that the throwing thread owns the monitor while the other thread (there are two threads in the program) sleeps. How should I proceed? What do you usually do when you encounter similar threading issues?

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• Controlling race condition at startup.

  - by Will Hartung

  I have some code that I want to have some one time initialisation performed. But this code doesn't have a definite lifecycle, so my logic can be potentially invoked by multiple threads before my initialisation is done. So, I want to basically ensure that my logic code "waits" until initialisation is done. This is my first cut. public class MyClass { private static final AtomicBoolean initialised = new AtomicBoolean(false); public void initialise() { synchronized(initialised) { initStuff(); initialised.getAndSet(true); initialised.notifyAll(); } } public void doStuff() { synchronized(initialised) { if (!initialised.get()) { try { initialised.wait(); } catch (InterruptedException ex) { throw new RuntimeException("Uh oh!", ex); } } } doOtherStuff(); } } I basically want to make sure this is going to do what I think it's going to do -- block doStuff until the initialised is true, and that I'm not missing a race condition where doStuff might get stuck on a Object.wait() that will never arrive. Edit: I have no control over the threads. And I want to be able to control when all of the initialisation is done, which is why doStuff() can't call initialise(). I used an AtomicBoolean as it was a combination of a value holder, and an object I could synchronize. I could have also simply had a "public static final Object lock = new Object();" and a simple boolean flag. AtomicBoolean conveniently gave me both. A Boolean can not be modified. The CountDownLatch is exactly what I was looking for. I also considered using a Sempahore with 0 permits. But the CountDownLatch is perfect for just this task.

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• Start and run a class member function in background, in QT/C++

  - by Regof

  Once a minute I want to run a task, not blocking other GUI functions. I heared somthing about QConcurent::run ... Or should I use signals and slots?

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• Keeping track of threads when creating them recursively

  - by 66replica

  I'm currently working on some code for my Programming Languages course. I can't post the code but I'm permitted to talk about some high level concepts that I'm struggling with and receive input on them. Basically the code is a recursive DFS on a undirected graph that I'm supposed to convert to a concurrent program. My professor already specified that I should create my threads in the recursive DFS method and then join them in another method. Basically, I'm having trouble thinking of how I should keep track of the threads I'm creating so I can join all of them in the other method. I'm thinking an array of Threads but I'm unsure how to add each new thread to the array or even if that's the right direction.

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• Multithreaded java cache for objects that are heavy to create ?

  - by krosenvold

  I need a cache some objects with fairly heavy creation times, and I need exactly-once creation semantics. It should be possible to create objects for different CacheKeys concurrently. I think I need something that (under the hood) does something like this: ConcurrentHashMap<CacheKey, Future<HeavyObject>> Are there any existing open-source implementations of this that I can re-use ?

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• Does OpenCL allow concurrent writes to same memory address?

  - by Wonko

  Is two (or more) different threads allowed to write to the same memory location in global space in OpenCL? The write is always changing a uchar from 0 to 1 so the outcome should be predictable, but I'm getting erratic results in my program, so I'm wondering if the reason can be that some of the writes fail. Could it help to declare the buffer write-only and copy it to a read-only buffer afterwards?

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• Waiting for a subset of threads in a Java ThreadPool

  - by David Semeria

  Let's say I have a thread pool containing X items, and a given task employs Y of these items (where Y is much smaller than X). I want to wait for all of the threads of a given task (Y items) to finish, not the entire thread pool. If the thread pool's execute() method returned a reference to the employed thread I could simply join() to each of these Y threads, but it doesn't. Does anyone know of an elegant way to accomplish this? Thanks.

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• Queue implementation with blocked 'take()' but with eviction policy

  - by mjlee

  Is there an implementation with a blocking queue for take but bounded by a maximum size. However, when the maximum size is reached, instead of blocking, it will remove from the head. One usage is that if I have a very slow consumer, the system will not crash ( runs out of memory ) rather these message will be removed.

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• java -> System.gc(); Does this call opens a new Thread or not?

  - by ogzylz

  For example I such a code ... get some memory and lose all the pointers to that memory so that System.gc(); can collect it. call System.gc(); do some other tasks; Here does the "do some other tasks;" and "System.gc();" works in paralel or does the "do some other tasks;" waits for "System.gc();" to be executed Thank you

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• Are spinlocks a good choice for a memory allocator?

  - by dsimcha

  I've suggested to the maintainers of the D programming language runtime a few times that the memory allocator/garbage collector should use spinlocks instead of regular OS critical sections. This hasn't really caught on. Here are the reasons I think spinlocks would be better: At least in synthetic benchmarks that I did, it's several times faster than OS critical sections when there's contention for the memory allocator/GC lock. Edit: Empirically, using spinlocks didn't even have measurable overhead in a single-core environment, probably because locks need to be held for such a short period of time in a memory allocator. Memory allocations and similar operations usually take a small fraction of a timeslice, and even a small fraction of the time a context switch takes, making it silly to context switch in the case of contention. A garbage collection in the implementation in question stops the world anyhow. There won't be any spinning during a collection. Are there any good reasons not to use spinlocks in a memory allocator/garbage collector implementation?

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• Singletons with TimerManager on WebSphere Cluster

  - by sujan

  How can I get a timer task on a WebSphere cluster to execute once and only once? I know this is possible on other app servers but can't figure out how to do this in WebSphere.

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• What happens when I MPI_Send to a process that has finished?

  - by nieldw

  What happens when I MPI_Send to a process that has finished? I am learning MPI, and writing a small sugar distribution-simulation in C. When the factories stop producing, those processes end. When warehouses run empty, they end. Can I somehow tell if the shop's order to a warehouse did not succeed(because the warehouse process has ended) by looking at the return value of MPI_Send? The documentation doesn't mention a specific error code for this situation, but that no error is returned for success. Can I do: if (MPI_Send(...)) { ... /* destination has ended */ ... } And disregard the error code? Thanks

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