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  • Where can I find a good guide to writing C Collections?

    - by Mike Axiak
    I remember having read a very good guide to writing collections. By that I mean, it described using macros to generate types with type parameters, kind of like C++ templates. I'm not sure if it was written by Rusty Russell, but it was someone I recognized. It was posted on hackernews or proggit... I wanted to write a new C library and has searched google for the past 30 min for this guide to no avail. Anybody remember?

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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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  • What is a "could not find type System.Collections.Generic.List" in the .NET Designer?

    - by WindyCityEagle
    I've got a WinForms project that I've had for quite some time, and now suddenly, I can't open the designer anymore and when I try to open the designer I get an error that says could not find type 'System.Collections.Generic.List' All of the code builds just fine, but I can't use the designer anymore, and I don't know what happened, nor do I have any idea where to look to solve the problem. Has anyone ever run into this or have any insight?

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  • Adding Timestamp to Java's GC messages in Tomcat 6

    - by ripper234
    I turned on Java's GC log options -XX:+PrintGC -XX:+PrintGCTimeStamps -XX:+PrintGCDetails Which print out these messages to standard output (catalina.out): 314.884: [CMS-concurrent-mark-start] 315.014: [CMS-concurrent-mark: 0.129/0.129 secs] [Times: user=0.14 sys=0.00, real=0.13 secs] 315.014: [CMS-concurrent-preclean-start] 315.016: [CMS-concurrent-preclean: 0.003/0.003 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] 315.016: [CMS-concurrent-abortable-preclean-start] 332.055: [GC 332.055: [ParNew: 17128K->84K(19136K), 0.0017700 secs] 88000K->70956K(522176K) icms_dc=4 , 0.0018660 secs] [Times: user=0.00 sys=0.00, real=0.00 secs] CMS: abort preclean due to time 352.253: [CMS-concurrent-abortable-preclean: 0.023/37.237 secs] [Times: user=0.78 sys=0.02, real=37.23 secs] How can I make these log lines appear with an actual timestamp (including date) instead of these numbers, which presumably mean "time since JVM started" ?

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  • How do you handle files that can't support concurrent edits in Mercurial?

    - by Scott Whitlock
    I'm using Mercurial with TortoiseHg. Each developer has their own repositories, and there's one central repository on the server for synchronizing our changes. (This will sound lame, but we're using it to manage the source for a legacy VB6 project. Nothing we can do about that...) As has been pointed out elsewhere, there is a big problem in VB6 with merging the .frx (form resources) files. So code changes seem to merge fine, but if two developers both make changes at the same time in the form design view, we can't merge. I'm ok with disallowing concurrent edits, but of course the whole point of Mercurial is that it's distributed so there is no option to force a file to be locked before editing. I don't believe there's a Mercurial solution for this, so I'm wondering: other developers who are using Mercurial for version control, do you have some 3rd party tool that assists with locking files for editing in the cases where it's necessary? Did we make a mistake using Mercurial instead of something like SVN?

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  • Must all Concurrent Data Store (CDB) locks be explicitly released when closing a Berkeley DB?

    - by Steve Emmerson
    I have an application that comprises multiple processes each accessing a single Berkeley DB Concurrent Data Store (CDB) database. Each process is single-threaded and does no explicit locking of the database. When each process terminates normally, it calls DB-close() and DB_ENV-close(). When all processes have terminated, there should be no locks on the database. Episodically, however, the database behaves as if some process was holding a write-lock on it even though all processes have terminated normally. Does each process need to explicitly release all locks before calling DB_ENV-close()? If so, how does the process obtain the "locker" parameter for the call to DB_ENV-loc_vec()?

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  • SQlite/Firebird: Does any of them support multiple concurrent write access ?

    - by Quandary
    Question: I currently store ASP.net application data in XML files. Now the problem is I have asynchronous operations, which means I ran into the problem of simultanous write access on a XML file... Now, I'm considering moving to an embedded database to solve the issue. I'm currently considering SQlite and embeddable Firebird. I'm not sure however if SQlite or Firebird can handle multiple concurrent write access. And I certainly don't want the same problem again. Anybody knows ? SQlite certainly is better known, but which one is better - SQlite or Firebird ? I tend to say Firebird, but I don't really know. No MS-Access or MS-SQL-express recommodations please, I'm a sane person.

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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 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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  • Why use hashing to create pathnames for large collections of files?

    - by Stephen
    Hi, I noticed a number of cases where an application or database stored collections of files/blobs using a has to determine the path and filename. I believe the intended outcome is a situation where the path never gets too deep, or the folders ever get too full - too many files (or folders) in a folder making for slower access. EDIT: Examples are often Digital libraries or repositories, though the simplest example I can think of (that can be installed in about 30s) is the Zotero document/citation database. Why do this? EDIT: thanks Mat for the answer - does this technique of using a hash to create a file path have a name? Is it a pattern? I'd like to read more, but have failed to find anything in the ACM Digital Library

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  • Find top N elements in a Multiset from Google Collections?

    - by dfrankow
    A Google Collections Multiset is a set of elements each of which has a count (i.e. may be present multiple times). I can't tell you how many times I want to do the following Make a histogram (exactly Multiset) Get the top N values from the histogram Examples: top 10 URLs, top 10 tags, ... What is the canonical way to do #2 given a Multiset? Here is a blog post about it, but that code is not quite what I want. First, it returns everything, not just top N. Second, it copies (is it possible to avoid a copy?). Third, I usually want a deterministic sort, i.e. tiebreak if counts are equal.

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  • How to fix Solr - Server is shutting down issue?

    - by Krunal
    I was having a running Solr 4.1 on Windows Server 2008 R2. The Solr is deployed on Tomcat. However, today it stops suddenly, and while accessing Solr it gives following error. HTTP Status 503 - Server is shutting down type Status report message Server is shutting down description The requested service is not currently available. On further looking into Logs, we got following: Log File: tomcat7-stderr.2013-05-09.txt May 09, 2013 8:00:40 PM org.apache.solr.core.CoreContainer finalize SEVERE: CoreContainer was not shutdown prior to finalize(), indicates a bug -- POSSIBLE RESOURCE LEAK!!! instance=2221663 Log File: catalina.2013-05-09.txt May 09, 2013 7:59:25 PM org.apache.solr.core.SolrResourceLoader <init> INFO: new SolrResourceLoader for directory: 'c:\solrdir\' May 09, 2013 7:59:29 PM org.apache.solr.common.SolrException log SEVERE: Exception during parsing file: null:org.xml.sax.SAXParseException; systemId: file:/c:/solr/solr.xml; lineNumber: 2; columnNumber: 6; The processing instruction target matching "[xX][mM][lL]" is not allowed. at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source) at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPIData(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanPIData(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPI(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) at org.apache.solr.core.Config.<init>(Config.java:121) at org.apache.solr.core.CoreContainer.load(CoreContainer.java:428) at org.apache.solr.core.CoreContainer.load(CoreContainer.java:404) at org.apache.solr.core.CoreContainer$Initializer.initialize(CoreContainer.java:336) at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:98) at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:281) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:262) at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:107) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4656) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5309) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633) at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:977) at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1655) at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) May 09, 2013 7:59:29 PM org.apache.solr.servlet.SolrDispatchFilter init SEVERE: Could not start Solr. Check solr/home property and the logs May 09, 2013 7:59:29 PM org.apache.solr.common.SolrException log SEVERE: null:org.apache.solr.common.SolrException: at org.apache.solr.core.CoreContainer.load(CoreContainer.java:431) at org.apache.solr.core.CoreContainer.load(CoreContainer.java:404) at org.apache.solr.core.CoreContainer$Initializer.initialize(CoreContainer.java:336) at org.apache.solr.servlet.SolrDispatchFilter.init(SolrDispatchFilter.java:98) at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:281) at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:262) at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:107) at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4656) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5309) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633) at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:977) at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1655) at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source) at java.util.concurrent.FutureTask.run(Unknown Source) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: org.xml.sax.SAXParseException; systemId: file:/c:/solrdir/solr.xml; lineNumber: 2; columnNumber: 6; The processing instruction target matching "[xX][mM][lL]" is not allowed. at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source) at com.sun.org.apache.xerces.internal.util.ErrorHandlerWrapper.fatalError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLErrorReporter.reportError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.reportFatalError(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPIData(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanPIData(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLScanner.scanPI(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(Unknown Source) at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source) at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source) at org.apache.solr.core.Config.<init>(Config.java:121) at org.apache.solr.core.CoreContainer.load(CoreContainer.java:428) ... 20 more May 09, 2013 7:59:29 PM org.apache.solr.servlet.SolrDispatchFilter init INFO: SolrDispatchFilter.init() done May 09, 2013 7:59:29 PM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\docs May 09, 2013 7:59:30 PM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\manager May 09, 2013 7:59:30 PM org.apache.catalina.startup.HostConfig deployDirectory INFO: Deploying web application directory C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\webapps\ROOT May 09, 2013 7:59:30 PM org.apache.coyote.AbstractProtocol start INFO: Starting ProtocolHandler ["http-bio-8983"] May 09, 2013 7:59:30 PM org.apache.coyote.AbstractProtocol start INFO: Starting ProtocolHandler ["ajp-bio-8009"] May 09, 2013 7:59:30 PM org.apache.catalina.startup.Catalina start INFO: Server startup in 9578 ms May 09, 2013 8:00:40 PM org.apache.solr.core.CoreContainer finalize SEVERE: CoreContainer was not shutdown prior to finalize(), indicates a bug -- POSSIBLE RESOURCE LEAK!!! instance=2221663 Any idea what could be wrong and how to fix?

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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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  • Do entity collections and object sets implement IQueryable<T>?

    - by Chevex
    I am using Entity Framework for the first time and noticed that the entities object returns entity collections. DBEntities db = new DBEntities(); db.Users; //Users is an ObjectSet<User> User user = db.Users.Where(x => x.Username == "test").First(); //Is this getting executed in the SQL or in memory? user.Posts; //Posts is an EntityCollection<Post> Post post = user.Posts.Where(x => x.PostID == "123").First(); //Is this getting executed in the SQL or in memory? Do both ObjectSet and EntityCollection implement IQueryable? I am hoping they do so that I know the queries are getting executed at the data source and not in memory. EDIT: So apparently EntityCollection does not while ObjectSet does. Does that mean I would be better off using this code? DBEntities db = new DBEntities(); User user = db.Users.Where(x => x.Username == "test").First(); //Is this getting executed in the SQL or in memory? Post post = db.Posts.Where(x => (x.PostID == "123")&&(x.Username == user.Username)).First(); // Querying the object set instead of the entity collection. Also, what is the difference between ObjectSet and EntityCollection? Shouldn't they be the same? Thanks in advance!

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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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  • Hibernate - EhCache - Which region to Cache associations/sets/collections ??

    - by lifeisnotfair
    Hi all, I am a newcomer to hibernate. It would be great if someone could comment over the following query that i have: Say i have a parent class and each parent has multiple children. So the mapping file of parent class would be something like: parent.hbm.xml <hibernate-mapping > <class name="org.demo.parent" table="parent" lazy="true"> <cache usage="read-write" region="org.demo.parent"/> <id name="id" column="id" type="integer" length="10"> <generator class="native"> </generator> </id> <property name="name" column="name" type="string" length="50"/> <set name="children" lazy="true"> <cache usage="read-write" region="org.demo.parent.children" /> <key column="parent_id"/> <one-to-many class="org.demo.children"/> </set> </class> </hibernate-mapping> children.hbm.xml <hibernate-mapping > <class name="org.demo.children" table="children" lazy="true"> <cache usage="read-write" region="org.demo.children"/> <id name="id" column="id" type="integer" length="10"> <generator class="native"> </generator> </id> <property name="name" column="name" type="string" length="50"/> <many-to-one name="parent_id" column="parent_id" type="integer" length="10" not-null="true"/> </class> </hibernate-mapping> So for the set children, should we specify the region org.demo.parent.children where it should cache the association or should we use the cache region of org.demo.children where the children would be getting cached. I am using EHCache as the 2nd level cache provider. I tried to search for the answer to this question but couldnt find any answer in this direction. It makes more sense to use org.demo.children but I dont know in which scenarios one should use a separate cache region for associations/sets/collections as in the above case. Kindly provide your inputs also let me know if I am not clear in my question. Thanks all.

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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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  • JasperReports: is it possible to use multiple data sources, or if not, to use collections in paramet

    - by Knut Arne Vedaa
    It seems that the reporting idiom is that a report consist of a single list of items, with some additional data (parameters). Are there ways to include several unrelated lists in a report, or would this go against the idiom to such an extent that a different tool should rather be used to generate the output? Suppose, for instance, you have a list of Persons that lives in a Building, with names, phone numbers and so on. This list would be the main datasource. Additionally, on the same report you want to show various other information about that Building, such as address, number of floors and so on. The number of items in this information might vary between Buildings, so that you cannot simply put it into static parameters, but would need a map or a list. This is of course a contrieved example, but should serve to illustrate the problem. In short: can you use several unrelated lists in a report?

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