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  • Next in Concurrency

    - by Jatin
    For past year I have been working a lot on concurrency in Java and have build and worked on many concurrent packages. So in terms of development in the concurrent world, I am quite confident. Further I am very much interested to learn and understand more about concurrent programming. But I am unable to answer myself what next? What extra should I learn or work on to inherit more skills related to Multi-core processing. If there is any nice book (read and enjoyed 'concurrency in practice' and 'concurrent programming in java') or resource's related to Multi-core processing so that I can go to the next level?

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  • Deploying an EAR to JBOSS times out (org.rhq.core.pc.inventory.TimeoutException:)

    - by rangalo
    Hi, I am trying to deploy an ear file to JBOSS AS (defalut server). The application is the mavenised version of examples of SeamInAction book. When I copy the file to $JBOSS_HOME/server/default/deploy, I don't get any exception but the application doesn't respond, after some time trying to access the application from the browser gives following in the log... While deploying with admin-console (http://localhost:8080/admin-console) I get following error messgae: PS: After this Jboss gets into unusable state. I cannot even access admin-console. I just have to kill it. ErrorMessage in admin-console: Failed to create Resource Open18.ear - cause: org.rhq.core.pc.inventory.TimeoutException: Call to [org.rhq.plugins.jbossas5.ApplicationServerComponent.createResource()] with args [[CreateResourceReport: ResourceType=[ResourceType[id=0, category=Service, name=Enterprise Application (EAR), plugin=JBossAS5]], ResourceKey=[null]]] timed out. Invocation thread will be interrupted at org.rhq.core.pc.inventory.ResourceContainer$ResourceComponentInvocationHandler.invokeInNewThreadWithLock(ResourceContainer.java:437) at org.rhq.core.pc.inventory.ResourceContainer$ResourceComponentInvocationHandler.invoke(ResourceContainer.java:406) at $Proxy266.createResource(Unknown Source) at org.rhq.core.pc.inventory.CreateResourceRunner.call(CreateResourceRunner.java:113) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619) Error Logs: 4:08:58,555 INFO [TableMetadata] foreign keys: [fkaf42e01ba13c3380, fk_course_ref_facility] 14:08:58,555 INFO [TableMetadata] indexes: [course_pkey] 14:08:58,645 INFO [TableMetadata] table found: public.facility 14:08:58,645 INFO [TableMetadata] columns: [zip, phone, state, type, uri, city, country, id, price_range, address, county, description, nam e] 14:08:58,645 INFO [TableMetadata] foreign keys: [] 14:08:58,645 INFO [TableMetadata] indexes: [facility_pkey] 14:08:58,705 INFO [TableMetadata] table found: public.hole 14:08:58,705 INFO [TableMetadata] columns: [id, m_par, l_handicap, name, l_par, number, course_id, m_handicap] 14:08:58,705 INFO [TableMetadata] foreign keys: [fk_hole_ref_course, fk30f4c09c3f1200] 14:08:58,705 INFO [TableMetadata] indexes: [hole_pkey, uniq_hole_number] 14:08:58,764 INFO [TableMetadata] table found: public.tee 14:08:58,764 INFO [TableMetadata] columns: [hole_id, distance, tee_set_id] 14:08:58,764 INFO [TableMetadata] foreign keys: [fk1c014f8de7677, fk_tee_ref_hole, fk1c014c69de560, fk_tee_ref_tee_set] 14:08:58,764 INFO [TableMetadata] indexes: [tee_pkey] 14:08:58,826 INFO [TableMetadata] table found: public.tee_set 14:08:58,826 INFO [TableMetadata] columns: [id, color, m_slope_rating, l_slope_rating, name, course_id, m_course_rating, l_course_rating, p os] 14:08:58,826 INFO [TableMetadata] foreign keys: [fk_tee_set_ref_course, fkaa6881b79c3f1200] 14:08:58,826 INFO [TableMetadata] indexes: [tee_set_pkey, uniq_tee_set_pos, uniq_tee_set_color] 14:08:58,827 INFO [SchemaUpdate] schema update complete 14:08:58,829 INFO [NamingHelper] JNDI InitialContext properties:{java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory, java. naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces} 14:08:58,850 INFO [TomcatDeployment] deploy, ctxPath=/Open18 14:15:53,969 WARN [DiscoveryComponentProxyFactory] The discovery component for resource type [ResourceType[id=0, category=Service, name=Connector, plugin=JBossAS5]] has been blacklisted 14:15:53,970 WARN [InventoryManager] Failure during discovery for [Connector] Resources - failed after 300002 ms. org.rhq.core.pc.inventory.TimeoutException: Call to [org.rhq.plugins.jbossas5.ConnectorDiscoveryComponent.discoverResources()] with args [[org.rhq.core.pluginapi.inventory.ResourceDiscoveryContext@96db1]] timed out. Invocation thread will be interrupted at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ResourceDiscoveryComponentInvocationHandler.invokeInNewThread(DiscoveryComponentProxyFactory.java:208) at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ResourceDiscoveryComponentInvocationHandler.invoke(DiscoveryComponentProxyFactory.java:181) at $Proxy249.discoverResources(Unknown Source) at org.rhq.core.pc.inventory.InventoryManager.invokeDiscoveryComponent(InventoryManager.java:272) at org.rhq.core.pc.inventory.InventoryManager.executeComponentDiscovery(InventoryManager.java:1697) at org.rhq.core.pc.inventory.RuntimeDiscoveryExecutor.discoverForResource(RuntimeDiscoveryExecutor.java:218) at org.rhq.core.pc.inventory.RuntimeDiscoveryExecutor.discoverForResource(RuntimeDiscoveryExecutor.java:234) at org.rhq.core.pc.inventory.RuntimeDiscoveryExecutor.runtimeDiscover(RuntimeDiscoveryExecutor.java:134) at org.rhq.core.pc.inventory.RuntimeDiscoveryExecutor.call(RuntimeDiscoveryExecutor.java:94) at org.rhq.core.pc.inventory.RuntimeDiscoveryExecutor.call(RuntimeDiscoveryExecutor.java:51) at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) at java.util.concurrent.FutureTask.run(FutureTask.java:138) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98) at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:207) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) at java.lang.Thread.run(Thread.java:619) 14:15:53,981 WARN [NavigationContent] Unable to find node for deleted resource [Resource[id=-5, type=Connector, key=ajp://127.0.0.1:8009, name=ajp://127.0.0.1:8009, parent=JBoss Web]].

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  • What version control system is best designed to *prevent* concurrent editing?

    - by Fred Hamilton
    We've been using CVS (with TortoiseCVS interface) for years for both source control and wide-ranging document control (including binaries such as Word, Excel, Framemaker, test data, simulation results, etc.). Unlike typical version control systems, 99% of the time we want to prevent concurrent editing - when a user starts editing a file, the pre-edit version of the file becomes read only to everyone else. Many of the people who will be using this are not programmers or even that computer savvy, so we're also looking for a system that let's people simply add documents to the repository, check out and edit a document (unless someone else is currently editing it), and check it back in with a minimum of fuss. We've gotten this to work reasonably well with CVS + TortoiseCVS, but we're now considering Subversion and Mercurial (and open to others if they're a better fit) for their better version tracking, so I was wondering which one supported locking files most transparently. For example, we'd like exclusive locking enabled as the default, and we want to make it as difficult as possible for someone to accidentally start editing a file that someone else has checked out. For example when someone checks out a file for editing, it checks with the master database first even if they have not recently updated their sandbox. Maybe it even won't let a user check out a document if it's off the network and can't check in with the mothership.

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  • How to avoid concurrent execution of a time-consuming task without blocking?

    - by Diego V
    I want to efficiently avoid concurrent execution of a time-consuming task in a heavily multi-threaded environment without making threads wait for a lock when another thread is already running the task. Instead, in that scenario, I want them to gracefully fail (i.e. skip its attempt to execute the task) as fast as possible. To illustrate the idea considerer this unsafe (has race condition!) code: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing running = true; try { runExpensiveTask(); } finally { running = false; } } I though about using a variation of Double-Checked Locking (consider that running is a primitive 32-bit field, hence atomic, it could work fine even for Java below 5 without the need of volatile). It could look like this: private static boolean running = false; public void launchExpensiveTask() { if (running) return; // Do nothing synchronized (ThisClass.class) { if (running) return; running = true; try { runExpensiveTask(); } finally { running = false; } } } Maybe I should also use a local copy of the field as well (not sure now, please tell me). But then I realized that anyway I will end with an inner synchronization block, that still could hold a thread with the right timing at monitor entrance until the original executor leaves the critical section (I know the odds usually are minimal but in this case we are thinking in several threads competing for this long-running resource). So, could you think in a better approach?

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  • How do I prevent the concurrent execution of a javascript function?

    - by RyanV
    I am making a ticker similar to the "From the AP" one at The Huffington Post, using jQuery. The ticker rotates through a ul, either by user command (clicking an arrow) or by an auto-scroll. Each list-item is display:none by default. It is revealed by the addition of a "showHeadline" class which is display:list-item. HTML for the UL Looks like this: <ul class="news" id="news"> <li class="tickerTitle showHeadline">Test Entry</li> <li class="tickerTitle">Test Entry2</li> <li class="tickerTitle">Test Entry3</li> </ul> When the user clicks the right arrow, or the auto-scroll setTimeout goes off, it runs a tickForward() function: function tickForward(){ var $active = $('#news li.showHeadline'); var $next = $active.next(); if($next.length==0) $next = $('#news li:first'); $active.stop(true, true); $active.fadeOut('slow', function() {$active.removeClass('showHeadline');}); setTimeout(function(){$next.fadeIn('slow', function(){$next.addClass('showHeadline');})}, 1000); if(isPaused == true){ } else{ startScroll() } }; This is heavily inspired by Jon Raasch's A Simple jQuery Slideshow. Basically, find what's visible, what should be visible next, make the visible thing fade and remove the class that marks it as visible, then fade in the next thing and add the class that makes it visible. Now, everything is hunky-dory if the auto-scroll is running, kicking off tickForward() once every three seconds. But if the user clicks the arrow button repeatedly, it creates two negative conditions: Rather than advance quickly through the list for just the number of clicks made, it continues scrolling at a faster-than-normal rate indefinitely. It can produce a situation where two (or more) list items are given the .showHeadline class, so there's overlap on the list. I can see these happening (especially #2) because the tickForward() function can run concurrently with itself, producing different sets of $active and $next. So I think my question is: What would be the best way to prevent concurrent execution of the tickForward() method? Some things I have tried or considered: Setting a Flag: When tickForward() runs, it sets an isRunning flag to true, and sets it back to false right before it ends. The logic for the event handler is set to only call tickForward() if isRunning is false. I tried a simple implementation of this, and isRunning never appeared to be changed. The jQuery queue(): I think it would be useful to queue up the tickForward() commands, so if you clicked it five times quickly, it would still run as commanded but wouldn't run concurrently. However, in my cursory reading on the subject, it appears that a queue has to be attached to the object its queue applies to, and since my tickForward() method affects multiple lis, I don't know where I'd attach it.

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  • Hung JVM consuming 100% CPU

    - by Bogdan
    We have a JAVA server running on Sun JRE 6u20 on Linux 32-bit (CentOS). We use the Server Hotspot with CMS collector with the following options (I've only provided the relevant ones): -Xmx896m -Xss128k -XX:NewSize=384M -XX:MaxPermSize=96m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC Sometimes, after running for a while, the JVM seems to slip into a hung state, whereby even though we don't make any requests to the application, the CPU continues to spin at 100% (we have 8 logical CPUs, so it looks like only one CPU does the spinning). In this state the JVM doesn't respond to SIGHUP signals (kill -3) and we can't connect to it normally with jstack. We CAN connect with "jstack -F", but the output is dodgy (we can see lots of NullPointerExceptions from JStack apparently because it wasn't able to 'walk' some stacks). So the "jstack -F" output seems to be useless. We have run a stack dump from "gdb" though, and we were able to match the thread id that spins the CPU (we found that using "top" with a per-thread view - "H" option) with a thread stack that appears in the gdb result and this is how it looks like: Thread 443 (Thread 0x7e5b90 (LWP 26310)): #0 0x0115ebd3 in CompactibleFreeListSpace::block_size(HeapWord const*) const () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #1 0x01160ff9 in CompactibleFreeListSpace::prepare_for_compaction(CompactPoint*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #2 0x0123456c in Generation::prepare_for_compaction(CompactPoint*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #3 0x01229b2c in GenCollectedHeap::prepare_for_compaction() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #4 0x0122a7fc in GenMarkSweep::invoke_at_safepoint(int, ReferenceProcessor*, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #5 0x01186024 in CMSCollector::do_compaction_work(bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #6 0x011859ee in CMSCollector::acquire_control_and_collect(bool, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #7 0x01185705 in ConcurrentMarkSweepGeneration::collect(bool, bool, unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #8 0x01227f53 in GenCollectedHeap::do_collection(bool, bool, unsigned int, bool, int) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #9 0x0115c7b5 in GenCollectorPolicy::satisfy_failed_allocation(unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #10 0x0122859c in GenCollectedHeap::satisfy_failed_allocation(unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #11 0x0158a8ce in VM_GenCollectForAllocation::doit() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #12 0x015987e6 in VM_Operation::evaluate() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #13 0x01597c93 in VMThread::evaluate_operation(VM_Operation*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #14 0x01597f0f in VMThread::loop() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #15 0x015979f0 in VMThread::run() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #16 0x0145c24e in java_start(Thread*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #17 0x00ccd46b in start_thread () from /lib/libpthread.so.0 #18 0x00bc2dbe in clone () from /lib/libc.so.6 It seems that a JVM thread is spinning while doing some CMS related work. We have checked the memory usage on the box, there seems to be enough memory available and the system is not swapping. Has anyone come across such a situation? Does it look like a JVM bug? UPDATE I've obtained some more information about this problem (it happened again on a server that has been running for more than 7 days). When the JVM entered the "hung" state it stayed like that for 2 hours until the server was manually restarted. We have obtained a core dump of the process and the gc log. We tried to get a heap dump as well, but "jmap" failed. We tried to use jmap -F but then only a 4Mb file was written before the program aborted with an exception (something about the a memory location not being accessible). So far I think the most interesting information comes from the gc log. It seems that the GC logging stopped as well (possibly at the time when the VM thread went into the long loop): 657501.199: [Full GC (System) 657501.199: [CMS: 400352K->313412K(524288K), 2.4024120 secs] 660634K->313412K(878208K), [CMS Perm : 29455K->29320K(68568K)], 2.4026470 secs] [Times: user=2.39 sys=0.01, real=2.40 secs] 657513.941: [GC 657513.941: [ParNew: 314624K->13999K(353920K), 0.0228180 secs] 628036K->327412K(878208K), 0.0230510 secs] [Times: user=0.08 sys=0.00, real=0.02 secs] 657523.772: [GC 657523.772: [ParNew: 328623K->17110K(353920K), 0.0244910 secs] 642036K->330523K(878208K), 0.0247140 secs] [Times: user=0.08 sys=0.00, real=0.02 secs] 657535.473: [GC 657535.473: [ParNew: 331734K->20282K(353920K), 0.0259480 secs] 645147K->333695K(878208K), 0.0261670 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] .... .... 688346.765: [GC [1 CMS-initial-mark: 485248K(524288K)] 515694K(878208K), 0.0343730 secs] [Times: user=0.03 sys=0.00, real=0.04 secs] 688346.800: [CMS-concurrent-mark-start] 688347.964: [CMS-concurrent-mark: 1.083/1.164 secs] [Times: user=2.52 sys=0.09, real=1.16 secs] 688347.964: [CMS-concurrent-preclean-start] 688347.969: [CMS-concurrent-preclean: 0.004/0.005 secs] [Times: user=0.00 sys=0.01, real=0.01 secs] 688347.969: [CMS-concurrent-abortable-preclean-start] CMS: abort preclean due to time 688352.986: [CMS-concurrent-abortable-preclean: 2.351/5.017 secs] [Times: user=3.83 sys=0.38, real=5.01 secs] 688352.987: [GC[YG occupancy: 297806 K (353920 K)]688352.987: [Rescan (parallel) , 0.1815250 secs]688353.169: [weak refs processing, 0.0312660 secs] [1 CMS-remark: 485248K(524288K)] 783055K(878208K), 0.2131580 secs] [Times: user=1.13 sys =0.00, real=0.22 secs] 688353.201: [CMS-concurrent-sweep-start] 688353.903: [CMS-concurrent-sweep: 0.660/0.702 secs] [Times: user=0.91 sys=0.07, real=0.70 secs] 688353.903: [CMS-concurrent-reset-start] 688353.912: [CMS-concurrent-reset: 0.008/0.008 secs] [Times: user=0.01 sys=0.00, real=0.01 secs] 688354.243: [GC 688354.243: [ParNew: 344928K->30151K(353920K), 0.0305020 secs] 681955K->368044K(878208K), 0.0308880 secs] [Times: user=0.15 sys=0.00, real=0.03 secs] .... .... 688943.029: [GC 688943.029: [ParNew: 336531K->17143K(353920K), 0.0237360 secs] 813250K->494327K(878208K), 0.0241260 secs] [Times: user=0.10 sys=0.00, real=0.03 secs] 688950.620: [GC 688950.620: [ParNew: 331767K->22442K(353920K), 0.0344110 secs] 808951K->499996K(878208K), 0.0347690 secs] [Times: user=0.11 sys=0.00, real=0.04 secs] 688956.596: [GC 688956.596: [ParNew: 337064K->37809K(353920K), 0.0488170 secs] 814618K->515896K(878208K), 0.0491550 secs] [Times: user=0.18 sys=0.04, real=0.05 secs] 688961.470: [GC 688961.471: [ParNew (promotion failed): 352433K->332183K(353920K), 0.1862520 secs]688961.657: [CMS I suspect this problem has something to do with the last line in the log (I've added some "...." in order to skip some lines that were not interesting). The fact that the server stayed in the hung state for 2 hours (probably trying to GC and compact the old generation) seems quite strange to me. Also, the gc log stops suddenly with that message and nothing else gets printed any more, probably because the VM Thread gets into some sort of infinite loop (or something that takes 2+ hours).

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  • Does the chunk of the System.Collections.Concurrent.Partitioner need to be thread safe?

    - by Scott Chamberlain
    I am working with the Parallel libraries in .net 4 and I am creating a Partitioner and the example shown in the MSDN only has a chunk size of 1 (every time a new result is retrieved it hits the data source instead of the local cache. The version I am writing will pull 10000 SQL rows at a time then feed the rows from the cache until it is empty then pull another batch. Each partition in the Partitioner has its own chunk. I know every time I call to the IEnumerator in from the SQL data-source that needs to be thread safe but for use in a Parallel.ForEach do I need to make every call to the cache for the chunking thread safe?

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  • Is there an implementation of rapid concurrent syntactical sugar in scala? eg. map-reduce

    - by TiansHUo
    Passing messages around with actors is great. But I would like to have even easier code. Examples (Pseudo-code) val splicedList:List[List[Int]]=biglist.partition(100) val sum:Int=ActorPool.numberOfActors(5).getAllResults(splicedList,foldLeft(_+_)) where spliceIntoParts turns one big list into 100 small lists the numberofactors part, creates a pool which uses 5 actors and receives new jobs after a job is finished and getallresults uses a method on a list. all this done with messages passing in the background. where maybe getFirstResult, calculates the first result, and stops all other threads (like cracking a password)

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  • What sql server isolation level should I choose to prevent concurrent reads?

    - by Brian Bolton
    I have the following transaction: SQL inserts a 1 new record into a table called tbl_document SQL deletes all records matching a criteria in another table called tbl_attachment SQL inserts multiple records into the tbl_attachment Until this transaction finishes, I don't want others users to be aware of the (1) new records in tbl_document, (2) deleted records in tbl_attachment, and (3) modified records in tbl_attachment. Would Read Committed Isolation be the correct isolation level?

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  • Different cache concurrent strategies for root entity and its collection (Hibernate with EHCache)?

    - by grigory
    Given example from Hibernate docs and modifying it so that root level entity (Customer) is read-only while one of its collections (tickets) is read-write: @Entity @Cache(usage = CacheConcurrencyStrategy.READ_ONLY) public class Customer { ... @OneToMany(...) @Cache(usage = CacheConcurrencyStrategy.READ_WRITE) public SortedSet<Ticket> getTickets() { return tickets; } ... } Would collection of tickets get refreshed when accessing customer from cache?

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  • How do I view how many concurrent long polling requests there are on my server?

    - by Pascal
    My host is Joyent. My host says I have 15 process limit and prstat -J shows those processes but that doesn't tell me how many long polling requests are currently being served. I could record it myself but that would add alot of performance overhead. I need to know when the server is at its long polling limits. I know this limit occurs far before the memory or CPU is used up. From experimentation, I've already verified that the number of long polls open is NOT equivalant to the number of processes running, probably because each process has multiple threads, each serving a request. thanks.

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  • What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

    - by fabrizioM
    I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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  • "FOR UPDATE" v/s "LOCK IN SHARE MODE" : Allow concurrent threads to read updated "state" value of locked row

    - by shadesco
    I have the following scenario: User X logs in to the application from location lc1: call it Ulc1 User X (has been hacked, or some friend of his knows his login credential, or he just logs in from a different browser on his machine,etc.. u got the point) logs in at the same time from location lc2: call it Ulc2 I am using a main servlet which : - gets a connection from database pooling - sets autocommit to false - executes a command that goes through app layers: if all successful, set autocommit to true in a "finally" statement, and closes connection. Else if an exception happens, rollback(). In my database (mysql/innoDb) i have a "history" table, with row columns: id(primary key) |username | date | topic | locked The column "locked" has by default value "false" and it serves as a flag that marks if a specific row is locked or not. Each row is specific to a user (as u can see from the username column) So back to the scenario: --Ulc1 sends the command to update his history from the db for date "D" and topic "T". --Ulc2 sends the same command to update history from the db for the same date "D" and same topic "T" at the exact same time. I want to implement an mysql/innoDB locking system that will enable whichever thread arriving to do the following check: Is column "locked" for this row true or not? if true, return a message to the user that " he is already updating the same data from another location" if not true (ie not locked) : flag it as locked and update then reset locked to false once finished. Which of these two mysql locking techniques, will actually allow the 2nd arriving thread from reading the "updated" value of the locked column to decide wt action to take?Should i use "FOR UPDATE" or "LOCK IN SHARE MODE"? This scenario explains what i want to accomplish: - Ulc1 thread arrives first: column "locked" is false, set it to true and continue updating process - Ulc2 thread arrives while Ulc1's transaction is still in process, and even though the row is locked through innoDb functionalities, it doesn't have to wait but in fact reads the "new" value of column locked which is "true", and so doesn't in fact have to wait till Ulc1 transaction commits to read the value of the "locked" column(anyway by that time the value of this column will already have been reset to false). I am not very experienced with the 2 types of locking mechanisms, what i understand so far is that LOCK IN SHARE MODE allow other transaction to read the locked row while FOR UPDATE doesn't even allow reading. But does this read gets on the updated value? or the 2nd arriving thread has to wait the first thread to commit to then read the value? Any recommendations about which locking mechanism to use for this scenario is appreciated. Also if there's a better way to "check" if the row has been locked (other than using a true/false column flag) please let me know about it. thank you SOLUTION (Jdbc pseudocode example based on @Darhazer's answer) Table : [ id(primary key) |username | date | topic | locked ] connection.setautocommit(false); //transaction-1 PreparedStatement ps1 = "Select locked from tableName for update where id="key" and locked=false); ps1.executeQuery(); //transaction 2 PreparedStatement ps2 = "Update tableName set locked=true where id="key"; ps2.executeUpdate(); connection.setautocommit(true);// here we allow other transactions threads to see the new value connection.setautocommit(false); //transaction 3 PreparedStatement ps3 = "Update tableName set aField="Sthg" where id="key" And date="D" and topic="T"; ps3.executeUpdate(); // reset locked to false PreparedStatement ps4 = "Update tableName set locked=false where id="key"; ps4.executeUpdate(); //commit connection.setautocommit(true);

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  • What are all the concurrent things [data structure, algorithm, locking mechanism] missing in .Net 3.

    - by user49767
    First time I am bit disappointed in StackOverflow cause my http://stackoverflow.com/questions/2571727/c-concurrency-vs-java-concurrency-which-is-neatly-designed-which-is-better question was closed. My intension was just trying to gather knowledge from programming guru's who worked in both the programming technologies. Rather closing this question, please help me by discussing what is good, bad, and ugly in multi-threading part in both the platforms. It is also welcome, if someone would like to compare with .Net 4.0 with JDK 6 (or JDK 7)

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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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  • jar dependencies in android- no class definition found exception

    - by Dave.B
    I'm trying to use the gdata java client library on android and have managed a decent hack to get it working. However because the jar for gdata had some package discrepancies with android I had to import the source into my project. This source is dependent on the JavaMail API and the JavaBeans Activation Framework as specified here. My issue is that the JavaMail jar throws a class definition not found when seeking a class which is in the Activation Framework jar. A stack trace is listed below. I am working in Eclipse and have both jars in a lib folder and added to my build path. I'm not very experienced dealing with jars in a situation like this so any help or insight would be appreciated. 03-29 09:55:26.204: ERROR/AndroidRuntime(331): Uncaught handler: thread AsyncTask #3 exiting due to uncaught exception 03-29 09:55:26.215: ERROR/AndroidRuntime(331): java.lang.RuntimeException: An error occured while executing doInBackground() 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at android.os.AsyncTask$3.done(AsyncTask.java:200) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.FutureTask.setException(FutureTask.java:124) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.FutureTask.run(FutureTask.java:137) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.lang.Thread.run(Thread.java:1096) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): Caused by: java.lang.NoClassDefFoundError: javax.activation.DataHandler 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at javax.mail.internet.MimeBodyPart.setContent(MimeBodyPart.java:684) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at com.google.gdata.data.media.MediaBodyPart.<init>(MediaBodyPart.java:95) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at com.google.gdata.data.media.MediaMultipart.<init>(MediaMultipart.java:126) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at com.google.gdata.client.media.MediaService.insert(MediaService.java:382) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at android.os.AsyncTask$2.call(AsyncTask.java:185) 03-29 09:55:26.215: ERROR/AndroidRuntime(331): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)

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  • openfire cannot subscribe gmail user

    - by cometta
    i trying to add gmail user with my local openfire, but get error below. I think something wrong with dns srv. can anyone suggest how to troubleshoot? </error> </presence> at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.java:217) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.returnErrorToSender(OutgoingSessionPromise.java:285) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.run(OutgoingSessionPromise.java:204) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:651) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:676) at java.lang.Thread.run(Thread.java:613) 2010.04.25 23:30:57 Error returning error to sender. Original packet: <presence id="lBI4K-24" to="[email protected]" type="subscribe" from="[email protected]"/> org.jivesoftware.openfire.PacketException: Cannot route packet of type IQ or Presence to bare JID: <presence id="lBI4K-24" to="[email protected]" from="[email protected]" type="error"> <error code="404" type="cancel"> <remote-server-not-found xmlns="urn:ietf:params:xml:ns:xmpp-stanzas"/> </error> </presence> at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.java:217) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.returnErrorToSender(OutgoingSessionPromise.java:285) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.run(OutgoingSessionPromise.java:219) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:651) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:676) at java.lang.Thread.run(Thread.java:613) 2010.04.25 23:31:56 Error returning error to sender. Original packet: <presence id="gmEsS-26" to="[email protected]" type="subscribe" from="[email protected]"/> org.jivesoftware.openfire.PacketException: Cannot route packet of type IQ or Presence to bare JID: <presence id="gmEsS-26" to="[email protected]" from="[email protected]" type="error"> <error code="404" type="cancel"> <remote-server-not-found xmlns="urn:ietf:params:xml:ns:xmpp-stanzas"/> </error> </presence> at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.java:217) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.returnErrorToSender(OutgoingSessionPromise.java:285) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.run(OutgoingSessionPromise.java:219) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:651) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:676) at java.lang.Thread.run(Thread.java:613) 2010.04.25 23:31:56 Error returning error to sender. Original packet: <presence id="gmEsS-27" to="[email protected]" type="subscribe" from="[email protected]"/> org.jivesoftware.openfire.PacketException: Cannot route packet of type IQ or Presence to bare JID: <presence id="gmEsS-27" to="[email protected]" from="[email protected]" type="error"> <error code="404" type="cancel"> <remote-server-not-found xmlns="urn:ietf:params:xml:ns:xmpp-stanzas"/> </error> </presence> at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.java:217) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.returnErrorToSender(OutgoingSessionPromise.java:285) at org.jivesoftware.openfire.server.OutgoingSessionPromise$PacketsProcessor.run(OutgoingSessionPromise.java:204) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:651) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:676) at java.lang.Thread.run(Thread.java:613)

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  • C#/.NET Little Wonders: A Redux

    - by James Michael Hare
    I gave my Little Wonders presentation to the Topeka Dot Net Users' Group today, so re-posting the links to all the previous posts for them. The Presentation: C#/.NET Little Wonders: A Presentation The Original Trilogy: C#/.NET Five Little Wonders (part 1) C#/.NET Five More Little Wonders (part 2) C#/.NET Five Final Little Wonders (part 3) The Subsequent Sequels: C#/.NET Little Wonders: ToDictionary() and ToList() C#/.NET Little Wonders: DateTime is Packed With Goodies C#/.NET Little Wonders: Fun With Enum Methods C#/.NET Little Wonders: Cross-Calling Constructors C#/.NET Little Wonders: Constraining Generics With Where Clause C#/.NET Little Wonders: Comparer<T>.Default C#/.NET Little Wonders: The Useful (But Overlooked) Sets The Concurrent Wonders: C#/.NET Little Wonders: The Concurrent Collections (1 of 3) - ConcurrentQueue and ConcurrentStack C#/.NET Little Wonders: The Concurrent Collections (2 of 3) - ConcurrentDictionary Tweet   Technorati Tags: .NET,C#,Little Wonders

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  • Using GMail's SMTP and IMAP servers in Notification Mailer

    - by Saroja Kandepuneni
    Overview GMail offers free, reliable, popular SMTP and IMAP services, because of which many people are interested to use it. GMail can be used when there are no in-house SMTP/IMAP servers for testing or debugging purposes. This blog explains how to install GMail SSL certificate in Concurrent Tier, testing the connection using a standalone program, running Mailer diagnostics and configuring GMail IMAP and SMTP servers for Workflow Notification Mailer Inbound and Outbound connections. GMail servers configuration SMTP server Host Name  smtp.gmail.com SSL Port  465 TLS/SSL required  Yes User Name  Your full email address (including @gmail.com or @your_domain.com) Password  Your gmail passwor  IMAP server  Host Name imap.gmail.com  SSL Port 993 TLS/SSL Required Yes  User Name  Your full email address (including @gmail.com or @your_domain.com)  Password Your gmail password GMail SSL Certificate Installation The following is the procedure to install the GMail SSL certificate Copy the below GMail SSL certificate to a file eg: gmail.cer -----BEGIN CERTIFICATE-----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-----END CERTIFICATE----- Install the SSL certificate into the default JRE location or any other location using below command Installing into a dfeault JRE location in EBS instance         # keytool -import -trustcacerts -keystore $AF_JRE_TOP/lib/security/cacerts  -storepass changeit -alias gmail-lnx_chainnedcert -file gmail.cer Install into a custom location         # keytool -import -trustcacerts -keystore <customLocation>  -storepass changeit -alias gmail-lnx_chainnedcert -file gmail.cer       <customLocation> -- directory in instance where the certificate need to be installed After running the above command you can see the following response         Trust this certificate? [no]:  yes        Certificate was added to keystore Running Mailer Command Line Diagnostics Run Mailer command line diagnostics from conccurrent tier where Mailer is running, to check the IMAP connection using the below command $AFJVAPRG -classpath $AF_CLASSPATH -Dprotocol=imap -Ddbcfile=$FND_SECURE/$TWO_TASK.dbc -Dserver=imap.gmail.com -Dport=993 -Dssl=Y -Dtruststore=$AF_JRE_TOP/lib/security/cacerts -Daccount=<gmail username> -Dpassword=<password> -Dconnect_timeout=120 -Ddebug=Y -Dlogfile=GmailImapTest.log -DdebugMailSession=Y oracle.apps.fnd.wf.mailer.Mailer Run Mailer command line diagnostics from concurrent tier where Mailer is running, to check the SMTP connection using the below command   $AFJVAPRG -classpath $AF_CLASSPATH -Dprotocol=smtp -Ddbcfile=$FND_SECURE/$TWO_TASK.dbc -Dserver=smtp.gmail.com -Dport=465 -Dssl=Y -Dtruststore=$AF_JRE_TOP/lib/security/cacerts -Daccount=<gmail username> -Dpassword=<password> -Dconnect_timeout=120 -Ddebug=Y -Dlogfile=GmailSmtpTest.log -DdebugMailSession=Y oracle.apps.fnd.wf.mailer.Mailer Standalone program to verify the IMAP connection Run the below standalone program from the concurrent tier node where Mailer is running to verify the connection with GMail IMAP server. It connects to the Gmail IMAP server with the given GMail user name and password and lists all the folders that exist in that account. If the Gmail IMAP server is not working for the  Mailer check whether the PROCESSED and DISCARD folders exist for the GMail account, if not create manually by logging into GMail account.Sample program to test GMail IMAP connection  The standalone program can be run as below  $java GmailIMAPTest GmailUsername GMailUserPassword            Standalone program to verify the SMTP connection Run the below standalone program from the concurrent tier node where Mailer is running to verify the connection with GMail SMTP server. It connects to the GMail SMTP server by authenticating with the given user name and password  and sends a test email message to the give recipient user email address. Sample program to test GMail SMTP connection The standalone program can be run as below  $java GmailSMTPTest GmailUsername gMailPassword recipientEmailAddress    Warnings As gmail.com is an external domain, the Mailer concurrent tier should allow the connection with GMail server Please keep in mind when using it for corporate facilities, that the e-mail data would be stored outside the corporate network

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  • Java web start - Unable to load resource

    - by CD
    Hi all, I've got a jar that loads great with java web starter when I browse through the IP address of the server. Once I try the server name instead I get the following exception: com.sun.deploy.net.FailedDownloadException: Unable to load resource: at com.sun.deploy.net.DownloadEngine.actionDownload(Unknown Source) at com.sun.deploy.net.DownloadEngine.getCacheEntry(Unknown Source) at com.sun.deploy.net.DownloadEngine.getCacheEntry(Unknown Source) at com.sun.deploy.net.DownloadEngine.getResourceCacheEntry(Unknown Source) at com.sun.deploy.net.DownloadEngine.getResourceCacheEntry(Unknown Source) at com.sun.deploy.net.DownloadEngine.getResource(Unknown Source) at com.sun.javaws.LaunchDownload$DownloadTask.call(Unknown Source) at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Any idea what should I look for?

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  • WCF Service Throttling

    - by Mubashar Ahmad
    Dear All I have a WCF Service Deployed in a Console App with BasicHTTPBinding and SSL enabled on port using NetSH command and more over following attribute is set as well. [AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)] And also i have set the Throttling behavior as <serviceThrottling maxConcurrentCalls="2147483647" maxConcurrentSessions="2147483647" maxConcurrentInstances="2147483647" /> On the other hand i have created a Test Client(for load test) that initiates multiple clients simultaneously(multiple threads) and performs transactions on server. everything seems fine and working properly but on server the CPU utilization is doesn't grow so i added some logging to view the number of concurrent calls to the server and found that its never went over 6. i have reviewed the performance counter logging code more than twice and it seems fine to me. So i want to ask where is the problem in this situation and one more thing i haven't specified any kind of ContextMode or ConcurrencyMode yet. After this Post I noticed that whenever i start another Intance of Test Client my concurrent Server Calls counter increase to 2 like if i am running only 1 instance the maximum Concurrent Rcvd Calls will be 2 and if there are two instance the same value goes to 4 and so on. Is there any limit of Number of WCF Calls from once process? Looking for help Mubashar *Added on 17-March******************* Today i ran another test with one test client(with 50 concurrent users) on the same machine on which the server is running this time i am getting exact result what i wanted it to show i.e. Maximum concurrent Calls Rcvd by Server = 50 but i need to do it the same on others machines as well. Can anybody help me on this.

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