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  • What is optimal hardware configuration for heavy load LAMP application

    - by Piotr Kochanski
    I need to run Linux-Apache-PHP-MySQL application (Moodle e-learning platform) for a large number of concurrent users - I am aiming 5000 users. By concurrent I mean that 5000 people should be able to work with the application at the same time. "Work" means not only do database reads but writes as well. The application is not very typical, since it is doing a lot of inserts/updates on the database, so caching techniques are not helping to much. We are using InnoDB storage engine. In addition application is not written with performance in mind. For instance one Apache thread usually occupies about 30-50 MB of RAM. I would be greatful for information what hardware is needed to build scalable configuration that is able to handle this kind of load. We are using right now two HP DLG 380 with two 4 core processors which are able to handle much lower load (typically 300-500 concurrent users). Is it reasonable to invest in this kind of boxes and build cluster using them or is it better to go with some more high-end hardware? I am particularly curious how many and how powerful servers are needed (number of processors/cores, size of RAM) what network equipment should be used (what kind of switches, network cards) any other hardware, like particular disc storage solutions, etc, that are needed Another thing is how to put together everything, that is what is the most optimal architecture. Clustering with MySQL is rather hard (people are complaining about MySQL Cluster, even here on Stackoverflow).

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  • Newb Question: passing objects in java?

    - by Adam Outler
    Hello, I am new at java. I am doing the following: Read from file, then put data into a variable. checkToken = lineToken.nextToken(); processlinetoken() } But then when I try to process it... public static void readFile(String fromFile) throws IOException { BufferedReader reader = new BufferedReader(new FileReader(fromFile)); String line = null; while ((line=reader.readLine()) != null ) { if (line.length() >= 2) { StringTokenizer lineToken = new StringTokenizer (line); checkToken = lineToken.nextToken(); processlinetoken() ...... But here's where I come into a problem. public static void processlinetoken() checkToken=lineToken.nextToken(); } it fails out. Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method nextToken() is undefined for the type String at testread.getEngineLoad(testread.java:243) at testread.readFile(testread.java:149) at testread.main(testread.java:119) so how do I get this to work? It seems to pass the variable, but nothing after the . works.

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  • Editing a .class file directly, playing around with opcodes

    - by echox
    Hi, today I just tried to play a little bit around with the opcodes in compiled java class file. After inserting iinc 1,1 the java virtual machine responds with: Exception in thread "main" java.lang.ClassFormatError: Truncated class file at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632) at java.lang.ClassLoader.defineClass(ClassLoader.java:616) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141) at java.net.URLClassLoader.defineClass(URLClassLoader.java:283) at java.net.URLClassLoader.access$000(URLClassLoader.java:58) at java.net.URLClassLoader$1.run(URLClassLoader.java:197) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Could not find the main class: Test. Program will exit. This is my example source code: public class Test { public static void main(String[] args) { int i = 5; i++; i++; i++; System.out.println("Number: " + i + "\n"); } } The opcode for an increment is 0x84 + 2 bytes for operands. There's only one section in the resulting class file, which contains 0x84: [..] 8401 0184 0101 8401 01[..] So I would translate this as: iinc 1,1 iinc 1,1 iinc 1,1 corresponding to my i++; i++; i++; I then tried to append just 840101 to increment the variable once more, but that didn't work and resulted in the ClassFormatError. Is there anything like a checksum for the class file? I looked up the format of a classfile in http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html but could not find anything which points out to some kind of bytes_of_classfile or something. I also don't understand why the error is "Truncated Class File", because I did append something :-) I know its not a good idea to edit class files directly, but I'm just interested on the VM internals here.

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  • iphone crash log with dSym not loading debug information

    - by AngeDeLaMort
    Hello, I was trying to see why my application crashed on the device (iPhone) using the dSym generated along the executable (in ad hoc), but I don't know why, there isn't any useful information. It seems that "Organizer" is able to find the appropriate dSym and translate some data into more readable one, but when it comes to my application, I just have an address. Since I know how to reproduce it, I've tried to setup my build so it can help me in the future. So, I've tried to find if I had all the proper flags set int the project build properties and everything seems fine. So after doing some research, it seems that all information are stripped during link time and the dSym seems completely useless. I've played with some flags, but nothing changed. So, is there something special to do in order to get the crash file human readable? Or is it impossible in the ad hoc setting? The closest thing near to work that I've done was to build a debug version and look up the address in it. At least it seems to give the right file. So, I made a sample app and here what I have: (the line I want is #4): Thread 0 Crashed: 0 libobjc.A.dylib 0x00003ebc objc_msgSend + 20 1 UIKit 0x0005c970 -[UIView dealloc] + 60 2 UIKit 0x0005c840 -[UIImageView dealloc] + 76 3 CoreFoundation 0x0003963a -[NSObject release] + 28 4 MyApplication 0x000046a6 0x1000 + 13990 5 UIKit 0x00069750 -[UIViewController view] + 44 6 MyApplication 0x000053fa 0x1000 + 17402 The crash is made using 2 successive releases on an object. Thanks in advance.

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  • Hibernate NoMethod Error in Java

    - by Noor
    I am getting an error in hibernate and failing to know its origin stack trace: java.lang.NoSuchMethodError: org.hibernate.cfg.AnnotationBinder.bindDefaults(Lorg/hibernate/cfg/Mappings;)V at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1360) at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1826) at com.BiddingSystem.server.ServiceImpl.<init>(ServiceImpl.java:60) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at java.lang.Class.newInstance0(Class.java:355) at java.lang.Class.newInstance(Class.java:308) at org.mortbay.jetty.servlet.Holder.newInstance(Holder.java:153) at org.mortbay.jetty.servlet.ServletHolder.getServlet(ServletHolder.java:339) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:463) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:362) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:181) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:729) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:405) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) at org.mortbay.jetty.handler.RequestLogHandler.handle(RequestLogHandler.java:49) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) at org.mortbay.jetty.Server.handle(Server.java:324) at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:505) at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:843) at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:647) at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211) at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:380) at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:395) at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:488)

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  • In IIS6, how to provide authenticated access to static files on remote server

    - by frankadelic
    We have a library of ZIP files that we would like to make available for download at an ASP.NET site. The files are sitting on a NAS device that is accessible from out web farm. Here is our initial strategy: Map an IIS virtual directory to the shared drive at path /zipfiles Users can download the zip files when given the URL However, if users share links to the files, anyone can download them. We would instead like to make use of the ASP.NET forms authentication in our site to validate users' requests before initiating the file transfer. A few problems: A request for a zip file is handled by IIS, not ASP.NET. So it is not subject to forms authentication. In addition, we don't want ASP.NET to handle the request, because it uses up an ASP.NET thread and is not scalable for download of large files. So, configuring the asp.net dll to handle *.zip requests is not an option. Any ideas on this? One idea we've tossed around is this: Initial request for download will be for an ashx handler. This handler will, after authentication, generate a download token which is saved to a database. Then, the user is redirected to the file with token appended in QueryString (e.g. /files/xyz.zip?token=123456789). An ISAPI plugin will be used to check the token. Also, the token will expire after x amount of time. Any thoughts on this? I have not implemented an ISAPI plugin so I'm not sure if this will even work. I would like to avoid custom coding since security is an issue and I'd prefer to use a time-tested solution.

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  • Has form post behavior changed in modern browsers? (or How are double clicks handled by the browser)

    - by Alex Czarto
    Background: We are in the process of writing a registration/payment page, and our philosophy was to code all validation and error checking on the server side first, and then add client side validation as a second step (un-obstructive jQuery). We wanted to disable double clicks server side, so we wrote some locking, thread-safe code to handle simultaneous posts/race conditions. When we tried to test this, we realized that we could not cause a simultaneous post or race condition to occur. I thought that (in older browsers anyway) double clicking a submit button worked as follows: User double clicks submit button. Browser sends a post on the first click On the second click, browser cancels/ignores initial post, and initiates a second post (before the first post has returned with a response). Browser waits for second post to return, ignoring initial post response. I thought that from the server side it looked like this: Server gets two simultaneous post requests, executes and responds to them both (unaware that no one is listening to the first response). From our testing (FireFox 3.0, IE 8.0) this is what actually happens: User double clicks submit button Browser sends a post for the first click Browser queues up second click, but waits for the response from the first click. Response returns from first click (response is ignored?). Browser sends a post for the second click. So from a server side: Server receives a single post which it executes and responds to. Then, server receives a second request wich it executes and responds to. My question is, has this always worked this way (and I'm losing my mind)? Or is this a new feature in modern browsers that prevents simultaneous posts to be sent to the server? It seems that for server side double click prevention, we don't have to worry about simultaneous posts or race conditions. Only need to worry about queued up posts. Thanks in advance for any feedback / comments. Alex

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  • Are Fortran control characters (carriage control) still implemented in compilers?

    - by CmdrGuard
    In the book Fortran 95/2003 for Scientists and Engineers, there is much talk given to the importance of recognizing that the first column in a format statement is reserved for control characters. I've also seen control characters referred to as carriage control on the internet. To avoid confusion, by control characters, I refer to the characters "1, a blank (i.e. \s), 0, and +" as having an effect on the vertical spacing of output when placed in the first column (character) of a FORMAT statement. Also, see this text-only web page written entirely in fixed-width typeface : Fortran carriage-control (because nothing screams accuracy and antiquity better than prose in monospaced font). I found this page and others like it to be not quite clear. According to Fortran 95/2003 for Scientists and Engineers, failure to recall that the first column is reserved for carriage control can lead to horrible unintended output. Paraphrasing Dave Barry, type the wrong character, and nuclear missiles get fired at Norway. However, when I attempt to adhere to this stern warning, I find that gfortran has no idea what I'm talking about. Allow me to illustrate my point with some example code. I am trying to print out the number Pi: PROGRAM test_format IMPLICIT NONE REAL :: PI = 2 * ACOS(0.0) WRITE (*, 100) PI WRITE (*, 200) PI WRITE (*, 300) PI 100 FORMAT ('1', "New page: ", F11.9) 200 FORMAT (' ', "Single Space: ", F11.9) 300 FORMAT ('0', "Double Space: ", F11.9) END PROGRAM test_format This is the output: 1New page: 3.141592741 Single Space: 3.141592741 0Double Space: 3.141592741 The "1" and "0" are not typos. It appears that gfortran is completely ignoring the control character column. My question, then, is this: Are control characters still implemented in standards compliant compilers or is gfortran simply not standards compliant? For clarity, here is the output of my gfortran -v Using built-in specs. Target: powerpc-apple-darwin9 Configured with: ../gcc-4.4.0/configure --prefix=/sw --prefix=/sw/lib/gcc4.4 --mandir=/sw/share/man --infodir=/sw/share/info --enable-languages=c,c++,fortran,objc,java --with-gmp=/sw --with-libiconv-prefix=/sw --with-ppl=/sw --with-cloog=/sw --with-system-zlib --x-includes=/usr/X11R6/include --x-libraries=/usr/X11R6/lib --disable-libjava-multilib --build=powerpc-apple-darwin9 --host=powerpc-apple-darwin9 --target=powerpc-apple-darwin9 Thread model: posix gcc version 4.4.0 (GCC)

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  • Winsock tcp/ip Socket listening but connection refused, race condition?

    - by Wayne
    Hello folks. This involves two automated unit tests which each start up a tcp/ip server that creates a non-blocking socket then bind()s and listen()s in a loop on select() for a client that connects and downloads some data. The catch is that they work perfectly when run separately but when run as a test suite, the second test client will fail to connect with WSACONNREFUSED... UNLESS there is a Thread.Sleep() of several seconds between them??!!! Interestingly, there is retry loop every 1 second for connecting after any failure. So the second test loops for a while until timeout after 10 minutes. During that time, netstat -na shows the correct port number is in the LISTEN state for the server socket. So if it is in the listen state? Why won't it accept the connection? In the code, there are log messages that show the select NEVER even gets a socket ready to read (which means ready to accept a connection when it applies to a listening socket). Obviously the problem must be related to some race condition between finishing one test which means close() and shutdown() on each end of the socket, and the start up of the next. This wouldn't be so bad if the retry logic allowed it to connect eventually after a couple of seconds. However it seems to get "gummed up" and won't even retry. However, for some strange reason the listening socket SAYS it's in the LISTEN state even through keeps refusing connections. So that means it's the Windoze O/S which is actually catching the SYN packet and returning a RST packet (which means "Connection Refused"). The only other time I ever saw this error was when the code had a problem that caused hundreds of sockets to get stuck in TIME_WAIT state. But that's not the case here. netstat shows only about a dozen sockets with only 1 or 2 in TIME_WAIT at any given moment. Please help.

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  • Do I need Response.End() in ASP.Net 2.0

    - by Hamish Grubijan
    Hi, I am just starting with ASP.Net. I copied a ex-co-worker's code (from .Net 1.1 era) and it has a Response.End(); in case of an error. There is also a: catch (Exception ex) { Response.Write(ex.Message); Response.End(); } at the end of Page_Load(object sender, System.EventArgs e) which always appends "Thread was aborted." or something like that at the end. I suspect that this worked differently before, or the error conditions were not tested very well. Anyhow, I was able to stop using Response.End(); in case when I do not like the GET parameters, and use return; instead. It seemed to do the right think in a simple case. Is this Ok in general? There are some problems with the code I copied, but I do not want to do a rewrite; I just want to get it running first and find wrinkles later. The Response.End(); caused a mental block for me, however, so I want to figure it out. I want to keep the catch all clause just in case, at least for now. I could also end the method with: catch (System.Threading.ThreadAbortException) { Response.End(); } catch (Exception ex) { Response.Write(ex.Message); Response.End(); } but that just seems extremely stupid, once you think about all of the exceptions being generated. Please give me a few words of wisdom. Feel free to ask if something is not clear. Thanks! P.S. Ex-coworker was not fired and is a good coder - one more reason to reuse his example.

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  • Rack middleware deadlock

    - by Joel
    I include this simple Rack Middleware in a Rails application: class Hello def initialize(app) @app = app end def call(env) [200, {"Content-Type" => "text/html"}, "Hello"] end end Plug it in inside environment.rb: ... Dir.glob("#{RAILS_ROOT}/lib/rack_middleware/*.rb").each do |file| require file end Rails::Initializer.run do |config| config.middleware.use Hello ... I'm using Rails 2.3.5, Webrick 1.3.1, ruby 1.8.7 When the application is started in production mode, everything works as expected - every request is intercepted by the Hello middleware, and "Hello" is returned. However, when run in development mode, the very first request works returning "Hello", but the next request hangs. Interrupting webrick while it is in the hung state yields this: ^C[2010-03-24 14:31:39] INFO going to shutdown ... deadlock 0xb6efbbc0: sleep:- - /usr/lib/ruby/gems/1.8/gems/actionpack-2.3.5/lib/action_controller/reloader.rb:31 deadlock 0xb7d1b1b0: sleep:J(0xb6efbbc0) (main) - /usr/lib/ruby/1.8/webrick/server.rb:113 Exiting /usr/lib/ruby/1.8/webrick/server.rb:113:in `join': Thread(0xb7d1b1b0): deadlock (fatal) from /usr/lib/ruby/1.8/webrick/server.rb:113:in `start' from /usr/lib/ruby/1.8/webrick/server.rb:113:in `each' from /usr/lib/ruby/1.8/webrick/server.rb:113:in `start' from /usr/lib/ruby/1.8/webrick/server.rb:23:in `start' from /usr/lib/ruby/1.8/webrick/server.rb:82:in `start' from /usr/lib/ruby/gems/1.8/gems/rack-1.0.1/lib/rack/handler/webrick.rb:14:in `run' from /usr/lib/ruby/gems/1.8/gems/rails-2.3.5/lib/commands/server.rb:111 from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `gem_original_require' from /usr/local/lib/site_ruby/1.8/rubygems/custom_require.rb:31:in `require' from script/server:3 Something to do with the class reloader in development mode. There is also mention of deadlock in the exception. Any ideas what might be causing this? Any recommendations as to the best approach to debug this?

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  • Escaping colons in hibernate createSQLQuery

    - by Stratosgear
    I am confused on how I can create an SQL statement containing colons. I am trying to create a view and I am using (notice the double colons): create view MyView as ( SELECT tableA.colA as colA, tableB.colB as colB, round(tableB.colD / 1024)::numeric, 2) as calcValue, FROM tableA, tableB WHERE tableA.colC = 'someValue' ); This is a postgres query and I am forced to use the double colons (::) in order to correctly run the statement. I then pass the above statement through: s.createSQLQuery(myQuery).executeUpdate(); and I get a: Exception in thread "main" org.hibernate.exception.DataException: \ could not execute native bulk manipulation query at org.hibernate.exception.SQLStateConverter.convert(\ SQLStateConverter.java:102) ... more stacktrace... with an output of my above statement changed as (notice the question mark): create view MyView as ( SELECT tableA.colA as colA, tableB.colB as colB, round(tableB.colD / 1024)?, 2) as calcValue, FROM tableA, tableB WHERE tableA.colC = 'someValue' ); Obviously, hibernate confuses my colons with named parameters. Is there a way to escape the colons (a google suggestion that mentions that a single colon is escaped as a double colon does NOT work) or another way of running this statement? Thanks.

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  • XCode can't find headers in /usr/include

    - by mindthief
    Hi all, I'm trying to use standard system header files in my C++ XCode project: #include <openssl/bio.h> #include <openssl/ssl.h> #include <openssl/err.h> The build fails and it complains: "Openssl/bio.h: No such file or directory" I added /usr/include to the "Header Search Paths" in Project settings, but that doesn't fix it. I COULD fix it by adding the whole path like: #include </usr/include/openssl/bio.h> -- but the project is full of similar includes and I don't want to change all of them this way. Also, I feel I shouldn't have to do this. Another way to fix it would be as another thread mentioned, which is to add /usr/include to User Header Search Paths. But if I do that, then I'd have to change all the angle brackets < to quotes "", which again seems like a hack. I mean, these are standard system header files so I feel it should be something simple, not requiring these kinds of hacks. Any ideas? Thanks!

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  • My java.util.Scanner won't work

    - by Kevin Steen Hansen
    Hello Stackoverflow my code is getting this error: Skriv din alder herunder og tryk enter: Exception in thread "main" java.util.NoSuchElementException at java.util.Scanner.throwFor(Scanner.java:907) at java.util.Scanner.next(Scanner.java:1530) at java.util.Scanner.nextInt(Scanner.java:2160) at java.util.Scanner.nextInt(Scanner.java:2119) at Tasteturindtastning.main(Tasteturindtastning.java:20) [Finished in 1.7s with exit code 1] Adn my code is: // Starter java som man plejer, læs i HejVerden.java public class Tasteturindtastning { public static void main(String[] arg) { /* Jeg skal nu angive en variable, men jeg kan ikke bestemme denne variable * Da jeg ønsker at indtastningen fra dette tastetur skal være variablen. * I stedet for int og double bruger jeg så java.util.Scanner, som aflæser * brugerens indtastninger. */ java.util.Scanner tastetur = new java.util.Scanner(System.in); // Printer en opgave/spørgsmål til brugeren System.out.println("Skriv din alder herunder og tryk enter:"); int alder; // Angiver et variablenavn alder = tastetur.nextInt(); // Angiver variablen med værdien fra indtastningen /* Herunder gør jeg brug af et if statement der tjekker værdien for * variablen alder, og ser om den er lig med eller højere end 18, og hvis * dette er tilfældet, så udprinter den en sætning */ if (alder >= 18) System.out.println("Du er myndig, da du er " + alder + " år gammel"); // Printes hvis han er 18 eller ældre } } Can snyone tell me what is wrong?

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  • JavaFX: JNLP file error

    - by jeff porter
    Hello everyone, I'm getting the following error when I upload a JavaFX app to a website, but I don't get it locally. I'm presuming that I'm missing something like the 'codebase' tag, but I'm not sure where it goes, can anyone help me out please? Java Console error: exception: JNLP file error: iShout_Foxpro_browser.jnlp. Please make sure the file exists and check if "codebase" and "href" in the JNLP file are correct.. java.io.FileNotFoundException: JNLP file error: iShout_Foxpro_browser.jnlp. Please make sure the file exists and check if "codebase" and "href" in the JNLP file are correct. at sun.plugin2.applet.JNLP2Manager.loadJarFiles(Unknown Source) at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Exception: java.io.FileNotFoundException: JNLP file error: iShout_Foxpro_browser.jnlp. Please make sure the file exists and check if "codebase" and "href" in the JNLP file are correct. HTML file source... <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>app_one</title> </head> <body> <script src="http://dl.javafx.com/1.3/dtfx.js"></script> <script> javafx( { archive: "app_one.jar", draggable: true, width: 480, height: 320, code: "app.Main", name: "app_one" } );

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  • Is there stl and utf8 friendly C++ Wrapper for ICU, or other powerful unicode library

    - by artyom
    Hello, I need a good Unicode library for C++. I need Transformations in Unicode sensitive way. For example sort all strings in case insensitive way and get their first characters for index. Convert to upper and to lower various Unicode strings. Split text in reasonable position -- words that would work for Chinese and Japanese as well. Formatting numbers, dates in locale sensitive way (should be thread safe). Transparent support of utf8 (primary internal representation). As far as I know the best library is ICU. However, I can't find normal developer friendly API documentation with examples. Also as far as I see, it is not too friendly with modern C++ design, work with STL and so on. Like this std::string msg; unistring umsg.from_utf8(msg); unistring::word_iterator wi; for(wi=umsg.words().begin(),n=0;wi!=usmg.words().wi_end(),n<10;++wi,++n) ; msg=umsg.substr(umsg.words().begin(),wi).to_utf8(); cout<<_("Five 10 words are ")<<msg; Does anybody know good STL friendly ICU wrapper released under Open Source license preferred permissive like MIT or Boost, but others LGPLv2 compatible are ok as well. Is there another high quality library similar to ICU? Platform: UNIX/POSIX, Windows support is not required. Thanks, Artyom Edit: Unfortunatly I wasn't logged in so I can't make asnver accepted... I had attached the ansver by myself.

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  • Atomic int writes on file

    - by Waneck
    Hello! I'm writing an application that will have to be able to handle many concurrent accesses to it, either by threads as by processes. So no mutex'es or locks should be applied to this. To make the use of locks go down to a minimum, I'm designing for the file to be "append-only", so all data is first appended to disk, and then the address pointing to the info it has updated, is changed to refer to the new one. So I will need to implement a small lock system only to change this one int so it refers to the new address. How is the best way to do it? I was thinking about maybe putting a flag before the address, that when it's set, the readers will use a spin lock until it's released. But I'm afraid that it isn't at all atomic, is it? e.g. a reader reads the flag, and it is unset on the same time, a writer writes the flag and changes the value of the int the reader may read an inconsistent value! I'm looking for locking techniques but all I find is either for thread locking techniques, or to lock an entire file, not fields. Is it not possible to do this? How do append-only databases handle this? Thanks! Cauê

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  • NPE with logging while launching webstart on jre7 update 40

    - by atulsm
    My application was running fine until I upgraded my jre to 7u40. When my application is initializing, it's doing Logger.getLogger("ClassName"), and I'm getting the following exception. java.lang.ExceptionInInitializerError at java.util.logging.Logger.demandLogger(Unknown Source) at java.util.logging.Logger.getLogger(Unknown Source) at com.company.Application.Applet.<clinit>(Unknown Source) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at com.sun.javaws.Launcher.executeApplication(Unknown Source) at com.sun.javaws.Launcher.executeMainClass(Unknown Source) at com.sun.javaws.Launcher.doLaunchApp(Unknown Source) at com.sun.javaws.Launcher.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.NullPointerException at java.util.logging.Logger.setParent(Unknown Source) at java.util.logging.LogManager$6.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.util.logging.LogManager.doSetParent(Unknown Source) at java.util.logging.LogManager.access$1100(Unknown Source) at java.util.logging.LogManager$LogNode.walkAndSetParent(Unknown Source) at java.util.logging.LogManager$LoggerContext.addLocalLogger(Unknown Source) at java.util.logging.LogManager$LoggerContext.addLocalLogger(Unknown Source) at java.util.logging.LogManager.addLogger(Unknown Source) at java.util.logging.LogManager$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.util.logging.LogManager.<clinit>(Unknown Source) The exception is coming from this line: private static Logger logger = Logger.getLogger(Applet.class.getName()); Could it be because of any sideeffects with fix http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8017174 ? A workaround is to open the java control center and enable logging. This is a concern since by default "Enable Logging" is unchecked. If I select "Enable Logging", the application starts fine.

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  • DB2 Driver Connection Hanging in Glassfish Connection Pool

    - by Ant
    We have an intermittent issue around the DB2 used from a Glassfish connection pool. What happens is this: Under situations where the database (DB2 on ZOS) is under stress, our application (which is a multi-threaded application using connections to DB2 via a Glassfish connection pool) stops doing anything. The following are observed: 1) Looking at the server using JConsole, we can see a thread waiting indefinitely in the DB2 driver's getConnection() method. We can also see that it has gained a lock on a Vector within the driver. Several other threads are also calling the getConnection() method in the driver, and are hanging waiting for the lock on the Vector to be released. 2) Looking at the database itself, we can see that there are connections from the Glassfish server open and waiting to be used. It seems that there is some sort of mismatch between the connection pool on Glassfish and the connections actually open to DB2. Has anyone come across this issue before? Or something similar? If you need any more information that I haven't provided, then please let me know!

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  • Concurrent WCF calls via shared channel

    - by Kent Boogaart
    I have a web tier that forwards calls onto an application tier. The web tier uses a shared, cached channel to do so. The application tier services in question are stateless and have concurrency enabled. But they are not being called concurrently. If I alter the web tier to create a new channel on every call, then I do get concurrent calls onto the application tier. But I wanted to avoid that cost since it is functionally unnecessary for my scenario. I have no session state, and nor do I need to re-authenticate the caller each time. I understand that the creation of the channel factory is far more expensive than than the creation of the channels, but it is still a cost I'd like to avoid if possible. I found this article on MSDN that states: While channels and clients created by the channels are thread-safe, they might not support writing more than one message to the wire concurrently. If you are sending large messages, particularly if streaming, the send operation might block waiting for another send to complete. Firstly, I'm not sending large messages (just a lot of small ones since I'm doing load testing) but am still seeing the blocking behavior. Secondly, this is rather open-ended and unhelpful documentation. It says they "might not" support writing more than one message but doesn't explain the scenarios under which they would support concurrent messages. Can anyone shed some light on this?

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  • Can I use POSIX signals in my Perl program to create event-driven programming?

    - by Shiftbit
    Is there any POSIX signals that I could utilize in my Perl program to create event-driven programming? Currently, I have multi-process program that is able to cross communicate but my parent thread is only able to listen to listen at one child at a time. foreach (@proc) { sysread(${$_}{'read'}, my $line, 100); #problem here chomp($line); print "Parent hears: $line\n"; } The problem is that the parent sits in a continual wait state until it receives it a signal from the first child before it can continue on. I am relying on 'pipe' for my intercommunication. My current solution is very similar to: http://stackoverflow.com/questions/2558098/how-can-i-use-pipe-to-facilitate-interprocess-communication-in-perl If possible I would like to rely on a $SIG{...} event or any non-CPAN solution. Update: As Jonathan Leffler mentioned, kill can be used to send a signal: kill USR1 = $$; # send myself a SIGUSR1 My solution will be to send a USR1 signal to my child process. This event tells the parent to listen to the particular child. child: kill USR1 => $parentPID if($customEvent); syswrite($parentPipe, $msg, $buffer); #select $parentPipe; print $parentPipe $msg; parent: $SIG{USR1} = { #get child pid? sysread($array[$pid]{'childPipe'}, $msg, $buffer); }; But how do I get my the source/child pid that signaled the parent? Have the child Identify itself in its message. What happens if two children signal USR1 at the same time?

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  • Trying to set PC clock programmatically just before Daylight Saving Time ends

    - by Moe Sisko
    To reproduce : 1) Add Microsoft.VisualBasic assembly to your project reference 2) Change PC timezone to : (GMT+10:00) Canberra, Melbourne, Sydney . Ensure PC is set to automatically adjust clock for daylight savings time. (For this timezone, daylight savings time ends at 3am on 4 Apr 2010.) 3) add following code : public void SetNewDateTime(DateTime dt) { Microsoft.VisualBasic.DateAndTime.Today = dt; // ignores time component Microsoft.VisualBasic.DateAndTime.TimeOfDay = dt; // ignores date component } private void button1_Click(object sender, EventArgs e) { DateTime dt = new DateTime(2010, 4, 5, 5, 0, 0); // XX SetNewDateTime(dt); // XX System.Threading.Thread.Sleep(500); DateTime dt2 = new DateTime(2010, 4, 4, 1, 0, 0); SetNewDateTime(dt2); } 4) When button 1 is clicked, the PC clock eventually shows 2am, whereas 1 am was expected. (If code marked at "XX" is removed, the clock sometimes shows the correct time of 1 am). Any idea what is happening ? (Or is there a more reliable way of setting the PC clock from C# code ?) TIA.

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  • .NET Splash screen issues

    - by CODe
    I have a splash screen for my C# database application that is called via the Shown event. The splash screen contains some information that is preprocessed when the main form's constructor is called, hence why I'm using the Shown event, because that information should be available. However, when the splash screen is shown, the main form is whited out, and the menu bar, bottom menu bar, and even the gray background are all white and invisible. It looks like the program is hanging, but after the 5 second delay I have built in, the banner goes away and the program is shown normally. Also, on the banner, I have labels that are not shown when the splash screen displays... Here is my code, some reasoning behind why it isn't working would help greatly. SPLASH SCREEN CODE : public partial class StartupBanner : Form { public StartupBanner(int missingNum, int expiredNum) { InitializeComponent(); missingLabel.Text = missingNum.ToString() + " MISSING POLICIES"; expiredLabel.Text = expiredNum.ToString() + " EXPIRED POLICIES"; } } CALLING CODE : private void MainForm_Shown(object sender, EventArgs e) { StartupBanner startup = new StartupBanner(missingPoliciesNum, expiredPoliciesNum); startup.MdiParent = this; startup.Show(); Thread.Sleep(5000); startup.Close(); } Using startup.ShowDialog() shows the correct label information on the splash screen, but that locks up the application, and I need the splash to go away after about 5 seconds, which is why it's a splash. ;)

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  • Java Polynomial Multiplication with ArrayList

    - by user1506919
    I am having a problem with one of my methods in my program. The method is designed to take 2 arraylists and the perform multiplication between the two like a polynomial. For example, if I was to say list1={3,2,1} and list2={5,6,7}; I am trying to get a return value of 15,28,38,20,7. However, all I can get is an error message that says: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0. I have provided the method below: private static ArrayList<Integer> multiply(ArrayList<Integer> list1,ArrayList<Integer> list2) { ArrayList<Integer> array =new ArrayList<Integer>(list1.size()+list2.size()); for (int i=0;i<array.size();i++) array.add(i, 0); for (int i = 0; i < list1.size(); i++) for (int j = 0; j < list2.size(); j++) array.set(i+j, ((list1.get(i) * list2.get(j))+array.get(i+j))); return array; } Any help with solving this problem is greatly appreciated.

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  • How to make safe frequent DataSource switches for AbstractRoutingDataSource?

    - by serg555
    I implemented Dynamic DataSource Routing for Spring+Hibernate according to this article. I have several databases with same structure and I need to select which db will run each specific query. Everything works fine on localhost, but I am worrying about how this will hold up in real web site environment. They are using some static context holder to determine which datasource to use: public class CustomerContextHolder { private static final ThreadLocal<CustomerType> contextHolder = new ThreadLocal<CustomerType>(); public static void setCustomerType(CustomerType customerType) { Assert.notNull(customerType, "customerType cannot be null"); contextHolder.set(customerType); } public static CustomerType getCustomerType() { return (CustomerType) contextHolder.get(); } public static void clearCustomerType() { contextHolder.remove(); } } It is wrapped inside some ThreadLocal container, but what exactly does that mean? What will happen when two web requests call this piece of code in parallel: CustomerContextHolder.setCustomerType(CustomerType.GOLD); //<another user will switch customer type here to CustomerType.SILVER in another request> List<Item> goldItems = catalog.getItems(); Is every web request wrapped into its own thread in Spring MVC? Will CustomerContextHolder.setCustomerType() changes be visible to other web users? My controllers have synchronizeOnSession=true. How to make sure that nobody else will switch datasource until I run required query for current user? Thanks.

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