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  • How to recover gracefully from a C# udp socket exception

    - by Gearoid Murphy
    Context: I'm porting a linux perl app to C#, the server listens on a udp port and maintains multiple concurrent dialogs with remote clients via a single udp socket. During testing, I send out high volumes of packets to the udp server, randomly restarting the clients to observe the server registering the new connections. The problem is this: when I kill a udp client, there may still be data on the server destined for that client. When the server tries to send this data, it gets an icmp "no service available" message back and consequently an exception occurs on the socket. I cannot reuse this socket, when I try to associate a C# async handler with the socket, it complains about the exception, so I have to close and reopen the udp socket on the server port. Is this the only way around this problem?, surely there's some way of "fixing" the udp socket, as technically, UDP sockets shouldn't be aware of the status of a remote socket? Any help or pointers would be much appreciated. Thanks.

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  • WCF Transaction Scope SQL insert table lock

    - by lihnid
    Hi All, I have two services talking to two different Data-stores (i.e SQL). I am using transactionscope: eg: using(TransactionScope scope = new TransactionScope()) { service1.InsertUser(user);//Insert to SQL Service 1 table User service2.SavePayment(payment);//Save payment SQL Service 2 table payment scope.Complete(); } Service1 is locking the table (User) until the transaction is completed making subsequent transactions with that table sequential. Is there a way to overcome the lock, so can have more than one concurrent calls to the SQL service1 table while the above code is executing? I would appreciate any input. Thanks in Advance. Lihnid

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  • Lua API for TokyoTyrant

    - by jideel
    Hi SO folks, I didn't managed to find an Lua client/api for TokyoTyrant. Such Api exists for TokyoCabinet, but not for TT. And Perl and Ruby API exists for TT. TT provides a native binary protocol, a memcached-compatible protocol, and an HTTP-oriented protocol. So my questions are : 1/ Do you think using the memcached (using luamemcached) or the HTTP protocol (using luaSocket) is "enough" for most / simple usage, and so a native Lua api is not necessary ? (the app is a simple uuid storage/distributor) ? 2/ Does it make sense to not use TokyoTyrant, but only TokyoCabinet, and use Lua at the application level to provide network and concurrent access to TC, using, say, Copas (Copas is , from their website, "a dispatcher based on coroutines that can be used by TCP/IP servers." ? Thanks.

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  • SqlServer / MySql Connection pool: is it really important ?

    - by stighy
    Hy guys, after a lot of problem with my hoster, i decided to disable connection pooling of my application. The problem was related to the number of concurrent connections : only five. So i decided to disable connection pooling: the result is that my web app don't crash. So i'm asking you: are there some "collateral" effect disabling connection pooling ? Is it so important ? I didn't noticed bad performance after disabling it. Thank you for your (i'm sure) precious advice!

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  • Light-weight client/server DB?

    - by OverTheRainbow
    Hello, (This question falls between programming and finding a tool, so I guess I'll ask here in SO since it has more activity than SuperUser.) I like the simplicity of SQLite, but by design, it doesn't support concurrent access. The apps I write don't have heavy needs, so I'd like to avoid heavier solutions like MySQL that are more difficult to deploy (remote customers with usually no computer personnel). Does someone know of a good solution that would offer the following features? Client available for VB.Net applications The server itself doesn't have to be a .Net application. Actually, I'd rather a bare-metal server so that it can run even on embedded Linux hosts with less RAM/CPU than regular PC's Easy install: the client part should either be statically linked inside the client application or be available as a single DLL, and the server should just be a single EXE listening for queries, à la Fossil (http://www.fossil-scm.org) clients can locate the server on the LAN by broadcasting data picked up by the server, so users don't have to write down the IP address and paste it into each client open-source, or moderately priced closed-source Thank you.

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  • Haskell typeclass

    - by Geoff
    I have a Haskell typeclass question. I can't munge the syntax to get this (seemingly reasonable) program to compile under GHC. import Control.Concurrent.MVar blah1 :: [a] -> IO ([a]) blah1 = return blah2 :: [a] -> IO (MVar [a]) blah2 = newMVar class Blah b where blah :: [a] -> IO (b a) instance Blah [] where blah = blah1 -- BOOM instance Blah (MVar []) where blah = blah2 main :: IO () main = do putStrLn "Ok" I get the following error message, which kind of makes sense, but I don't know how to fix it: `[]' is not applied to enough type arguments Expected kind `*', but `[]' has kind `* -> *' In the type `MVar []' In the instance declaration for `Blah (MVar [])'

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  • Java - JPA - When we need more than one EntityManager?

    - by Yatendra Goel
    I am learning JPA and have one question: In which situations we need more than one EntityManager in our application? The two situations that I am aware of are as follows: When our application is a multi-threaded application and more than one thread needs JPA transaction because EntityManager is not thread-safe and we need one EntityManager per thread. When any of the thread needs multiple concurrent transactions, we need more than one EntityManager in that thread because there is one-to-one relationship between EntityManager and EntityTransaction. Q1. Are there any other situations when we need more than one EntityManager? ================================================================================= Q2. Upto my understanding, there should be only one EntityManagerFactory per Persitence Unit. Am I correct? If not, then what are those situations when we need multiple EntityManagerFactory per Persistence Unit?

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  • Node.js vs PHP processing speed

    - by Cody Craven
    I've been looking into node.js recently and wanted to see a true comparison of processing speed for PHP vs Node.js. In most of the comparisons I had seen, Node trounced Apache/PHP set ups handily. However all of the tests were small 'hello worlds' that would not accurately reflect any webpage's markup. So I decided to create a basic HTML page with 10,000 hello world paragraph elements. In these tests Node with Cluster was beaten to a pulp by PHP on Nginx utilizing PHP-FPM. So I'm curious if I am misusing Node somehow or if Node is really just this bad at processing power. Note that my results were equivalent outputting "Hello world\n" with text/plain as the HTML, but I only included the HTML as it's closer to the use case I was investigating. My testing box: Core i7-2600 Intel CPU (has 8 threads with 4 cores) 8GB DDR3 RAM Fedora 16 64bit Node.js v0.6.13 Nginx v1.0.13 PHP v5.3.10 (with PHP-FPM) My test scripts: Node.js script var cluster = require('cluster'); var http = require('http'); var numCPUs = require('os').cpus().length; if (cluster.isMaster) { // Fork workers. for (var i = 0; i < numCPUs; i++) { cluster.fork(); } cluster.on('death', function (worker) { console.log('worker ' + worker.pid + ' died'); }); } else { // Worker processes have an HTTP server. http.Server(function (req, res) { res.writeHead(200, {'Content-Type': 'text/html'}); res.write('<html>\n<head>\n<title>Speed test</title>\n</head>\n<body>\n'); for (var i = 0; i < 10000; i++) { res.write('<p>Hello world</p>\n'); } res.end('</body>\n</html>'); }).listen(80); } This script is adapted from Node.js' documentation at http://nodejs.org/docs/latest/api/cluster.html PHP script <?php echo "<html>\n<head>\n<title>Speed test</title>\n</head>\n<body>\n"; for ($i = 0; $i < 10000; $i++) { echo "<p>Hello world</p>\n"; } echo "</body>\n</html>"; My results Node.js $ ab -n 500 -c 20 http://speedtest.dev/ This is ApacheBench, Version 2.3 <$Revision: 655654 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Licensed to The Apache Software Foundation, http://www.apache.org/ Benchmarking speedtest.dev (be patient) Completed 100 requests Completed 200 requests Completed 300 requests Completed 400 requests Completed 500 requests Finished 500 requests Server Software: Server Hostname: speedtest.dev Server Port: 80 Document Path: / Document Length: 190070 bytes Concurrency Level: 20 Time taken for tests: 14.603 seconds Complete requests: 500 Failed requests: 0 Write errors: 0 Total transferred: 95066500 bytes HTML transferred: 95035000 bytes Requests per second: 34.24 [#/sec] (mean) Time per request: 584.123 [ms] (mean) Time per request: 29.206 [ms] (mean, across all concurrent requests) Transfer rate: 6357.45 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 0 0.2 0 2 Processing: 94 547 405.4 424 2516 Waiting: 0 331 399.3 216 2284 Total: 95 547 405.4 424 2516 Percentage of the requests served within a certain time (ms) 50% 424 66% 607 75% 733 80% 813 90% 1084 95% 1325 98% 1843 99% 2062 100% 2516 (longest request) PHP/Nginx $ ab -n 500 -c 20 http://speedtest.dev/test.php This is ApacheBench, Version 2.3 <$Revision: 655654 $> Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/ Licensed to The Apache Software Foundation, http://www.apache.org/ Benchmarking speedtest.dev (be patient) Completed 100 requests Completed 200 requests Completed 300 requests Completed 400 requests Completed 500 requests Finished 500 requests Server Software: nginx/1.0.13 Server Hostname: speedtest.dev Server Port: 80 Document Path: /test.php Document Length: 190070 bytes Concurrency Level: 20 Time taken for tests: 0.130 seconds Complete requests: 500 Failed requests: 0 Write errors: 0 Total transferred: 95109000 bytes HTML transferred: 95035000 bytes Requests per second: 3849.11 [#/sec] (mean) Time per request: 5.196 [ms] (mean) Time per request: 0.260 [ms] (mean, across all concurrent requests) Transfer rate: 715010.65 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 0 0 0.2 0 1 Processing: 3 5 0.7 5 7 Waiting: 1 4 0.7 4 7 Total: 3 5 0.7 5 7 Percentage of the requests served within a certain time (ms) 50% 5 66% 5 75% 5 80% 6 90% 6 95% 6 98% 6 99% 6 100% 7 (longest request) Additional details Again what I'm looking for is to find out if I'm doing something wrong with Node.js or if it is really just that slow compared to PHP on Nginx with FPM. I certainly think Node has a real niche that it could fit well, however with these test results (which I really hope I made a mistake with - as I like the idea of Node) lead me to believe that it is a horrible choice for even a modest processing load when compared to PHP (let alone JVM or various other fast solutions). As a final note, I also tried running an Apache Bench test against node with $ ab -n 20 -c 20 http://speedtest.dev/ and consistently received a total test time of greater than 0.900 seconds.

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  • Spring App error: java.lang.NoClassDefFoundError: org/springframework/security/core/SpringSecurityCoreVersion

    - by Shades88
    I am writing a simple spring mvc login form example. I am getting below error in netbeans 05-Jun-2014 02:11:51.055 SEVERE [http-nio-8084-exec-1] org.apache.catalina.core.StandardContext.listenerStart Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener org.springframework.beans.factory.BeanDefinitionStoreException: Unexpected exception parsing XML document from ServletContext resource [/WEB-INF/SpringSecurity.xml]; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [org.springframework.security.config.SecurityNamespaceHandler]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: org/springframework/security/core/SpringSecurityCoreVersion at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:413) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:335) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:303) at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:180) at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216) at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:187) at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:125) at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:94) at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:129) at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:540) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:454) at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:403) at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:306) at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:106) at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4738) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5158) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:726) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:702) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:697) at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:579) at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:455) at org.apache.catalina.startup.HostConfig.check(HostConfig.java:1554) at sun.reflect.GeneratedMethodAccessor53.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) at org.apache.catalina.manager.ManagerServlet.check(ManagerServlet.java:1428) at org.apache.catalina.manager.ManagerServlet.deploy(ManagerServlet.java:885) at org.apache.catalina.manager.ManagerServlet.doGet(ManagerServlet.java:343) at javax.servlet.http.HttpServlet.service(HttpServlet.java:618) at javax.servlet.http.HttpServlet.service(HttpServlet.java:725) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:301) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:108) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:615) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:136) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:74) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:610) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:516) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1015) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:652) at org.apache.coyote.http11.Http11NioProtocol$Http11ConnectionHandler.process(Http11NioProtocol.java:222) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1575) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1533) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) at java.lang.Thread.run(Thread.java:744) Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [org.springframework.security.config.SecurityNamespaceHandler]: Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: org/springframework/security/core/SpringSecurityCoreVersion at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:164) at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:105) at org.springframework.beans.factory.xml.DefaultNamespaceHandlerResolver.resolve(DefaultNamespaceHandlerResolver.java:130) at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1419) at org.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1414) at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:187) at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:141) at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:110) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions(XmlBeanDefinitionReader.java:508) at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:391) ... 60 more Caused by: java.lang.NoClassDefFoundError: org/springframework/security/core/SpringSecurityCoreVersion at org.springframework.security.config.SecurityNamespaceHandler.<init>(SecurityNamespaceHandler.java:65) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:526) at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:148) ... 69 more Caused by: java.lang.ClassNotFoundException: org.springframework.security.core.SpringSecurityCoreVersion at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1284) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1132) ... 75 more I am using spring 3.2.7. It was not having spring security jar. So I got it downloaded using maven. It's version is 3.2.4. What is this error? There's no error in code. What must have gone wrong? For last 3 hours I have been trying to run a simple example, but totally hammered by this error. Please help

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  • Serial port : Read data problem, not reading complete data

    - by Anuj Mehta
    Hi I have an application where I am sending data via serial port from PC1 (Java App) and reading that data in PC2 (C++ App). The problem that I am facing is that my PC2 (C++ App) is not able to read complete data sent by PC1 i.e. from my PC1 I am sending 190 bytes but PC2 is able to read close to 140 bytes though I am trying to read in a loop. Below is code snippet of my C++ App Open the connection to serial port serialfd = open( serialPortName.c_str(), O_RDWR | O_NOCTTY | O_NDELAY); if (serialfd == -1) { /* * Could not open the port. */ TRACE << "Unable to open port: " << serialPortName << endl; } else { TRACE << "Connected to serial port: " << serialPortName << endl; fcntl(serialfd, F_SETFL, 0); } Configure the Serial Port parameters struct termios options; /* * Get the current options for the port... */ tcgetattr(serialfd, &options); /* * Set the baud rates to 9600... */ cfsetispeed(&options, B38400); cfsetospeed(&options, B38400); /* * 8N1 * Data bits - 8 * Parity - None * Stop bits - 1 */ options.c_cflag &= ~PARENB; options.c_cflag &= ~CSTOPB; options.c_cflag &= ~CSIZE; options.c_cflag |= CS8; /* * Enable hardware flow control */ options.c_cflag |= CRTSCTS; /* * Enable the receiver and set local mode... */ options.c_cflag |= (CLOCAL | CREAD); // Flush the earlier data tcflush(serialfd, TCIFLUSH); /* * Set the new options for the port... */ tcsetattr(serialfd, TCSANOW, &options); Now I am reading data const int MAXDATASIZE = 512; std::vector<char> m_vRequestBuf; char buffer[MAXDATASIZE]; int totalBytes = 0; fcntl(serialfd, F_SETFL, FNDELAY); while(1) { bytesRead = read(serialfd, &buffer, MAXDATASIZE); if(bytesRead == -1) { //Sleep for some time and read again usleep(900000); } else { totalBytes += bytesRead; //Add data read to vector for(int i =0; i < bytesRead; i++) { m_vRequestBuf.push_back(buffer[i]); } int newBytesRead = 0; //Now keep trying to read more data while(newBytesRead != -1) { //clear contents of buffer memset((void*)&buffer, 0, sizeof(char) * MAXDATASIZE); newBytesRead = read(serialfd, &buffer, MAXDATASIZE); totalBytes += newBytesRead; for(int j = 0; j < newBytesRead; j++) { m_vRequestBuf.push_back(buffer[j]); } }//inner while break; } //while

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  • How is thread synchronization implemented, at the assembly language level?

    - by Martin
    While I'm familiar with concurrent programming concepts such as mutexes and semaphores, I have never understood how they are implemented at the assembly language level. I imagine there being a set of memory "flags" saying: lock A is held by thread 1 lock B is held by thread 3 lock C is not held by any thread etc But how is access to these flags synchronized between threads? Something like this naive example would only create a race condition: mov edx, [myThreadId] wait: cmp [lock], 0 jne wait mov [lock], edx ; I wanted an exclusive lock but the above ; three instructions are not an atomic operation :(

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  • Infinispan equivalent to ehcache's copyOnRead and copyOnWrite

    - by waxwing
    Hi, I am planning to implement a cache solution into an existing web app. Nothing complicated: basically a concurrent map that supports overflowing to disk and automatic eviction. Clustering the cache could be requirement in the future, but not now. I like ehcache's copyOnRead and copyOnWrite features, because it means that I don't have to manually clone things before modifying something I take out of the cache. Now I have started to look at Infinispan, but I have not found anything equivalent there. Does it exist? I.e., the following unit tests should pass: @Test public void testCopyOnWrite() { Date date = new Date(0); cache.put(0, date); date.setTime(1000); date = cache.get(0); assertEquals(0, date.getTime()); } @Test public void testCopyOnRead() { Date date = new Date(0); cache.put(0, date); assertNotSame(cache.get(0), cache.get(0)); }

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  • ZooKeeper and RabbitMQ/Qpid together - overkill or a good combination?

    - by Chris Sears
    Greetings, I'm evaluating some components for a multi-data center distributed system. We're going to be using message queues (via either RabbitMQ or Qpid) so agents can make asynchronous requests to other agents without worrying about addressing, routing, load balancing or retransmission. In many cases, the agents will be interacting with components that were not designed for highly concurrent access, so locking and cross-agent coordination will be needed to avoid race conditions. Also, we'd like the system to automatically respond to agent or data center failures. With the above use cases in mind, ZooKeeper seemed like it might be a good fit. But I'm wondering if trying to use both ZK and message queuing is overkill. It seems like what Zookeeper does could be accomplished by my own cluster manager using AMQP messaging, but that would be hard to get really right. On the other hand, I've seen some examples where ZooKeeper was used to implement message queuing, but I think RabbitMQ/Qpid are a more natural fit for that. Has anyone out there used a combination like this? Thanks in advance, -Chris

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  • Run java thread at specific times

    - by rmarimon
    I have a web application that synchronizes with a central database four times per hour. The process usually takes 2 minutes. I would like to run this process as a thread at X:55, X:10, X:25, and X:40 so that the users knows that at X:00, X:15, X:30, and X:45 they have a clean copy of the database. It is just about managing expectations. I have gone through the executor in java.util.concurrent but the scheduling is done with the scheduleAtFixedRate which I believe provides no guarantee about when this is actually run in terms of the hours. I could use a first delay to launch the Runnable so that the first one is close to the launch time and schedule for every 15 minutes but it seems that this would probably diverge in time. Is there an easier way to schedule the thread to run 5 minutes before every quarter hour?

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  • Locking NFS files in PHP

    - by Oli
    Part of my latest webapp needs to write to file a fair amount as part of its logging. One problem I've noticed is that if there are a few concurrent users, the writes can overwrite each other (instead of appending to file). I assume this is because of the destination file can be open in a number of places at the same time. flock(...) is usually superb but it doesn't appear to work on NFS... Which is a huge problem for me as the production server uses a NFS array. The closest thing I've seen to an actual solution involves trying to create a lock dir and waiting until it can be created. To say this lacks elegance is understatement of the year, possibly decade. Any better ideas? Edit: I should add that I don't have root on the server and doing the storage in another way isn't really feasible any time soon, not least within my deadline.

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  • Web service performance testing plan, Microsoft .NET WS, SQL

    - by zxed
    Trying to answer a question to come up with a testing plan. It has to do with using a website and/or webservice that queries a sql server to get data and display to user. * Solution must be able to handle an estimated 2000 users, approximately 700 concurrent users, 10,000 + website hits a month. Database calls should handle 100,000 queries via the website/webservice a month. The system is used at multiple times during a 24 hour period; however networking and bandwidth traffic decreases after 5 pm * two windows 2003 servers are used, one for web, another for sql. Both are located in the same room. User access is varied and users can be far/near (its a centralized system), users access via www

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  • Lazy loading of child throwing session error

    - by Thomas Buckley
    I'm the following error when calling purchaseService.updatePurchase(purchase) inside my TagController: SEVERE: Servlet.service() for servlet [PurchaseAPIServer] in context with path [/PurchaseAPIServer] threw exception [Request processing failed; nested exception is org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.app.model.Purchase.tags, no session or session was closed] with root cause org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.app.model.Purchase.tags, no session or session was closed at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383) at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375) at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:368) at org.hibernate.collection.PersistentSet.add(PersistentSet.java:212) at com.app.model.Purchase.addTags(Purchase.java:207) at com.app.controller.TagController.createAll(TagController.java:79) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:212) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:900) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:827) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789) at javax.servlet.http.HttpServlet.service(HttpServlet.java:641) at javax.servlet.http.HttpServlet.service(HttpServlet.java:722) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:225) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:169) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:927) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:999) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:565) at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:309) 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:662) TagController: @RequestMapping(value = "purchases/{purchaseId}/tags", method = RequestMethod.POST, params = "manyTags") @ResponseStatus(HttpStatus.CREATED) public void createAll(@PathVariable("purchaseId") final Long purchaseId, @RequestBody final Tag[] entities) { Purchase purchase = purchaseService.getById(purchaseId); Set<Tag> tags = new HashSet<Tag>(Arrays.asList(entities)); purchase.addTags(tags); purchaseService.updatePurchase(purchase); } Purchase: @Entity @XmlRootElement public class Purchase implements Serializable { /** * */ private static final long serialVersionUID = 6603477834338392140L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @OneToMany(mappedBy = "purchase", fetch = FetchType.LAZY, cascade={CascadeType.ALL}) private Set<Tag> tags; @JsonIgnore public Set<Tag> getTags() { if (tags == null) { tags = new LinkedHashSet<Tag>(); } return tags; } public void setTags(Set<Tag> tags) { this.tags = tags; } ... } Tag: @Entity @XmlRootElement public class Tag implements Serializable { /** * */ private static final long serialVersionUID = 5165922776051697002L; @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @ManyToOne(fetch = FetchType.LAZY) @JoinColumns({@JoinColumn(name = "PURCHASEID", referencedColumnName = "ID")}) private Purchase purchase; @JsonIgnore public Purchase getPurchase() { return purchase; } public void setPurchase(Purchase purchase) { this.purchase = purchase; } } PurchaseService: @Service public class PurchaseService implements IPurchaseService { @Autowired private IPurchaseDAO purchaseDAO; public PurchaseService() { } @Transactional public List<Purchase> getAll() { return purchaseDAO.findAll(); } @Transactional public Purchase getById(Long id) { return purchaseDAO.findOne(id); } @Transactional public void addPurchase(Purchase purchase) { purchaseDAO.save(purchase); } @Transactional public void updatePurchase(Purchase purchase) { purchaseDAO.update(purchase); } } TagService: @Service public class TagService implements ITagService { @Autowired private ITagDAO tagDAO; public TagService() { } @Transactional public List<Tag> getAll() { return tagDAO.findAll(); } @Transactional public Tag getById(Long id) { return tagDAO.findOne(id); } @Transactional public void addTag(Tag tag) { tagDAO.save(tag); } @Transactional public void updateTag(Tag tag) { tagDAO.update(tag); } } Any ideas on how I can fix this? (I want to avoid using EAGER loading). Do I need to setup some form of session management for transactions? Thanks

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  • Why does my finite state machine take so long to execute?

    - by BillyONeal
    Hello all :) I'm working on a state machine which is supposed to extract function calls of the form /* I am a comment */ //I am a comment perf("this.is.a.string.which\"can have QUOTES\"", 123456); where the extracted data would be perf("this.is.a.string.which\"can have QUOTES\"", 123456); from a file. Currently, to process a 41kb file, this process is taking close to a minute and a half. Is there something I'm seriously misunderstanding here about this finite state machine? #include <boost/algorithm/string.hpp> std::vector<std::string> Foo() { std::string fileData; //Fill filedata with the contents of a file std::vector<std::string> results; std::string::iterator begin = fileData.begin(); std::string::iterator end = fileData.end(); std::string::iterator stateZeroFoundLocation = fileData.begin(); std::size_t state = 0; for(; begin < end; begin++) { switch (state) { case 0: if (boost::starts_with(boost::make_iterator_range(begin, end), "pref(")) { stateZeroFoundLocation = begin; begin += 4; state = 2; } else if (*begin == '/') state = 1; break; case 1: state = 0; switch (*begin) { case '*': begin = boost::find_first(boost::make_iterator_range(begin, end), "*/").end(); break; case '/': begin = std::find(begin, end, L'\n'); } break; case 2: if (*begin == '"') state = 3; break; case 3: switch(*begin) { case '\\': state = 4; break; case '"': state = 5; } break; case 4: state = 3; break; case 5: if (*begin == ',') state = 6; break; case 6: if (*begin != ' ') state = 7; break; case 7: switch(*begin) { case '"': state = 8; break; default: state = 10; break; } break; case 8: switch(*begin) { case '\\': state = 9; break; case '"': state = 10; } break; case 9: state = 8; break; case 10: if (*begin == ')') state = 11; break; case 11: if (*begin == ';') state = 12; break; case 12: state = 0; results.push_back(std::string(stateZeroFoundLocation, begin)); }; } return results; } Billy3

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  • What is a good motivating example for dataflow concurrency?

    - by Alex Miller
    I understand the basics of dataflow programming and have encountered it a bit in Clojure APIs, talks from Jonas Boner, GPars in Groovy, etc. I know it's prevalent in languages like Io (although I have not studied Io). What I am missing is a compelling reason to care about dataflow as a paradigm when building a concurrent program. Why would I use a dataflow model instead of a mutable state+threads+locks model (common in Java, C++, etc) or an actor model (common in Erlang or Scala) or something else? In particular, while I know of library support in the languages above (and Scala and Ruby), I don't know of a single program or library that is a poster child user of this model. Who is using it? Why do they find it better than the other models I mentioned?

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  • Polymorphism problem: How to check type of derived class?

    - by malymato
    Hi, this is my first question here :) I know that I should not check for object type but instead use dynamic_cast, but that would not solve my problem. I have class called Extension and interfaces called IExtendable and IInitializable, IUpdatable, ILoadable, IDrawable (the last four are basicly the same). If Extension implements IExtendable interface, it can extend itself with different Extension objects. The problem is that I want to allow the Extension which implements IExtendable to extend only with Extension that implements the same interfaces as the original Extension. You probably don't unerstand that mess so I try to explain it with code: class IExtendable { public: IExtendable(void); void AddExtension(Extension*); void RemoveExtensionByID(unsigned int); vector<Extension*>* GetExtensionPtr(){return &extensions;}; private: vector<Extension*> extensions; }; class IUpdatable { public: IUpdatable(void); ~IUpdatable(void); virtual void Update(); }; class Extension { public: Extension(void); virtual ~Extension(void); void Enable(){enabled=true;}; void Disable(){enabled=false;}; unsigned int GetIndex(){return ID;}; private: bool enabled; unsigned int ID; static unsigned int _indexID; }; Now imagine the case that I create Extension like this: class MyExtension : public Extension, public IExtendable, public IUpdatable, public IDrawable { public: MyExtension(void); virtual ~MyExtension(void); virtual void AddExtension(Extension*); virtual void Update(); virtual void Draw(); }; And I want to allow this class to extend itself only with Extensions that implements the same interfaces (or less). For example I want it to be able to take Extension which implements IUpdatable; or both IUpdatable and IDrawable; but e.g. not Extension which implements ILoadable. I want to do this because when e.g. Update() will be called on some Extension which implements IExtendable and IUpdateable, it will be also called on these Extensions which extends this Extension. So when I'm adding some Extension to Extension which implements IExtendable and some of the IUpdatable, ILoadable... I'm forced to check if Extension that is going to be add implements these interfaces too. So In the IExtendable::AddExtension(Extension*) I would need to do something like this: void IExtendable::AddExtension(Extension* pEx) { bool ok = true; // check wheather this extension can take pEx // do this with every interface if ((*pEx is IUpdatable) && (*this is_not IUpdatable)) ok = false; if (ok) this->extensions.push_back(pEx); } But how? Any ideas what would be the best solution? I don't want to use dynamic_cast and see if it returns null... thanks

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  • Issue with SOAPUI: running test for concurrency

    - by Kangkan
    I am trying to test my web service using SOAPUI (the free version). For testing concurrency, I wished to fire concurrent threads from SOAPUI onto the service. But with the options, the thread count increases gradually (even in the burst mode). The machine where SOAPUI is installed is a WinXP machine. Can I actually do the concurrency testing? If so how? Please guide me. I am waiting for your answers and help.

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  • Named semaphores in Python?

    - by Boaz
    Hi, I have a script in python which uses a resource which can not be used by more than a certain amount of concurrent scripts running. Classically, this would be solved by a named semaphores but I can not find those in the documentation of the multiprocessing module or threading . Am I missing something or are named semaphores not implemented / exposed by Python? and more importantly, if the answer is no, what is the best way to emulate one? Thanks, Boaz PS. For reasons which are not so relevant to this question, I can not aggregate the task to a continuously running process/daemon or work with spawned processed - both of which, it seems, would have worked with the python API.

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  • WinUSB application or User-Mode Driver as a filter driver for USB Analysis/Sniffer/Trending

    - by Robert
    A question to maybe some who have worked extensively with WinUSB APIs or use mode USB drivers - Does anyone know if the WinUSB API or a user mode driver can be used as a passive observer of USB connections, capturing notification of interrupts, control requests, data transfers...etc without interfering with other applications (such as iTunes) which would obviously require concurrent access to the device at the same time my application is monitoring the connection and displaying data on it? Or do you pretty much have to write a kernel-mode filter driver and inject yourself in the USB stack in order to make that happen? In the past, there have been a few credible options (libusb-win32 and usbsnoop to be specific) though both are built around the old DDK, not the Windows Driver Foundation, and are not really supported on a regular basis any more. I'm hesitant to build something significant around them, as a result.

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  • Disk-based caching of dynamic images in IIS 7

    - by Daniel Schierbeck
    I'm writing an image server which needs to handle a relatively large number of concurrent requests (~5,000). The images being served are dynamically scaled down and cropped based on per-image specifications, which are queried from a database. The number of images is rather large, so an in-memory cache isn't viable (thrashing would most definitely occur). I'm using native caching in IIS 7 to avoid hitting the ASP.NET app which generates the images on-the-fly. I've looked around, but I couldn't find a simple way to configure IIS to store the cache on-disk -- is there such an option, or would I need to roll my own? I'd rather avoid placing the generated images in a public folder, so they can be served statically, since I would prefer to invalidate the cache entries using a query parameter (last-edit time from the database,) which doesn't seem possible to reconcile with static caching. I would love to get some feedback on this!

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  • Which web Tier Framework for a public commercial website with heavy load ?

    - by Maxime ARNSTAMM
    Hello everyone, As a part of an enterprise architecture exercise, i need to find a java-based framework filling these constraints : heavy (i think) load : 5000 concurrent connections widely known : can't be too exotic, the contractors would be too high priced. relatively easy to use : developpement time must be reasonnable must be as compliant as possible with the css/html layout produced by a designer Must look like "web 2.0" from the marketing point of view. What i learned from my limited experience is : jsf : 1, don't know. 2, 3 ok. 4 not ok (at least not without huge effort) wicket : 1, not really. 2, 3 and 4 ok. gwt : 1, don't know. 2, 3 ok. 4 not ok (but more ok than jsf) others : not really "web 2.0" or not really known I'm really junior, so my ideas about those frameworks are probably wrong, that's why i come to you, stackoverflowees. Thanks for helping :)

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