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• Servlet 3 spec and ThreadLocal

  - by mindas

  As far as I know, Servlet 3 spec introduces asynchronous processing feature. Among other things, this will mean that the same thread can and will be reused for processing another, concurrent, HTTP request(s). This isn't revolutionary, at least for people who worked with NIO before. Anyway, this leads to another important thing: no ThreadLocal variables as a temporary storage for the request data. Because if the same thread suddenly becomes the carrier thread to a different HTTP request, request-local data will be exposed to another request. All of that is my pure speculation based on reading articles, I haven't got time to play with any Servlet 3 implementations (Tomcat 7, GlassFish 3.0.X, etc.). So, the questions: Am I correct to assume that ThreadLocal will cease to be a convenient hack to keep the request data? Has anybody played with any of Servlet 3 implementations and tried using ThreadLocals to prove the above? Apart from storing data inside HTTP Session, are there any other similar easy-to-reach hacks you could possibly advise?

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• Sort/Enumerate an NSArray from somewhere in the middle?

  - by Kenny Winker

  I have an NSArray, with objects ordered like so: a b c d e f I would like to enumerate through this array in this order: c d e f a b i.e. starting at some point that is not the beginning, but hitting all the items. I imagine this is a matter of sorting first and then enumerating the array, but I'm not sure if that's the best technique... or, frankly, how to sort the array like this. Edit Adding details: These will be relatively small arrays, varying from 3 to 10 objects. No concurrent access. I'd like to permanently alter the sort order of the array each time I do this operation.

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• JPA in distributed Java EE configuration

  - by sof

  Hello, I'm developing a JEE application to run on Glassfish: Database (javaDB, MS SQL, MySQL or Oracle) EJB layer with JPA (Toplink essentials - from Glassfish) for database access JSF/Icefaces based web UI accessing the EJB layer The application will have a lot of concurrent web client, so I want to run it on different physical servers and use a load-balancer. My problem is now how to keep the applications synchronized. I intend to set up multiple servers, each running Glassfish with my EAR app installed. Whenever on one of the servers data is added to or removed from the database (via JPA, no direct SQL queries), this change should be reflected in the JPA layer on the other servers. I've been looking around for solutions to this, but couldn't find anything I really like (the full Toplink from Oracle claims to have a solution, but don't know). Doing a refresh before every access to a JPA entity could work, but is far from efficient. Are there any patterns, libraries, ... that could help here? Thanks a lot!

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• Suggest a open source project which heavily uses java concurrency utilities?

  - by user49767

  I have done good amount of Java programming, but yet to master Threading & Concurrency. I would like to become an expert programmer in threading & concurrency. I have also took a short at Tomcat code, I was able to understand, but looking even more complex project. Could you suggest any open source project which heavily uses java threading & concurrency utilities? Note : I have also reading java.util.concurrent package source code, but eager to learn from Application perspective, than creating my own threading utilities.

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• MySQL : incrementing text id in DB

  - by BarsMonster

  I need to have text IDs in my application. For example, we have acceptable charset azAZ09, and allowed range of IDs [aaa] - [cZ9]. First generated id would be aaa, then aab, aac, aad e.t.c. How one can return ID & increment lower bound in transaction-fashion? (provided that there are hundreds of concurrent requests and all should have correct result) To lower the load I guess it's possible to define say 20 separate ranges, and return id from random range - this should reduce contention, but it's not clear how to do single operation in the first place. Also, please note that number of IDs in range might exceed 2^32. Another idea is having ranges of 64-bit integers, and converting integer-char id in software code, where it could be done asyncroniously. Any ideas?

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• Query for Joining Two Tables With Possible Multiple Mapping

  - by Dharmendra Mohapatra

  First_table srno wono Actual_Start_Date Actual_End_Date 1 31 2012-06-02 2012-06-05 2 32 2012-06-05 2012-06-22 3 33 2012-06-11 2012-06-23 4 34 2012-06-23 2012-06-30 5 A-2 2012-06-24 2012-06-25 6 BU 2012-06-24 2012-06-26 7 40 2012-06-25 2012-06-27 second_table srno wono Base_start_date Base_end_date uploadhistoryid 1 31 2012-06-05 2012-06-05 1 2 32 2012-06-11 2012-06-12 2 3 32 2012-06-15 2012-06-17 3 4 32 2012-06-18 2012-06-20 4 5 33 2012-06-22 2012-06-25 5 5 33 2012-06-23 2012-06-25 5 Result Required SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO ALTER PROCEDURE [dbo].[Reports_Subanalysis] ( @WONo VARCHAR(20) ) AS BEGIN SELECT 'SAT' AS stage, s.Base_start_date AS start_date, s.Base_end_date AS end_date, f.Actual_Start_Date AS Actual_Start_Date, f.Actual_end_Date AS Actual_End_Date FROM First_table f, second_table B WHERE A.wOno=B.nOno AND f.uploadhistoryid in (SELECT min(uploadhistoryid) FROM second_table C WHERE f.wono = C.wono) AND b.wono=@WONo END when I pass '32' Result stage start_date end_date Actual_Start_Date Actual_End_Date SAT 2012-06-11 2012-06-12 2012-06-05 2012-06-05 how Can I get the result like this when I pass non matching value like 'BU' stage start_date end_date Actual_Start_Date Actual_End_Date SAT NULL NULL 2012-06-24 2012-06-26 What modification do I need in my routine?

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• List all files from a directory recursively with Java

  - by Hultner

  Okay I got this function who prints the name of all files in a directory recursively problem is that it's very slow and it gets the stuff from a network device and with my current code it has to access the device time after time. What I would want is to first load all the files from the directory recursively and then after that go through all files with the regex to filter out all the files I don't want. Unless anyone got a better suggestion. I've never before done anything like this. public static printFnames(String sDir){  File[] faFiles = new File(sDir).listFiles();  for(File file: faFiles){ if(file.getName().matches("^(.*?)")){   System.out.println(file.getAbsolutePath()); }   if(file.isDirectory()){     printFnames(file.getAbsolutePath());   }  } } This is just a test later on I'm not going to use the code like this, instead I'm going to add the path and modification date of every file which matches an advanced regex to an array.

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• Good code visualization / refactoring tools for C++?

  - by Paul D.

  I've found myself coming across a lot of reasonably large, complicated codebases at work recently which I've been asked to either review or refactor or both. This can be extremely time consuming when the code is highly concurrent, makes heavy use of templates (particularly static polymorphism) and has logic that depends on callbacks/signals/condition variables/etc. Are there any good visualization tools for C++ period, and of those are there any that actually play well with "advanced" C++ features? Anything would probably be better than my approach now, which is basically pen+paper or stepping through the debugger. The debugger method can be good for following a particular code path, but isn't great for seeing the big picture you really need when doing serious refactoring. EDIT: I should mention that Visual Studio plugins aren't going to be a lot of help to me, since our stuff is mostly Linux-only.

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• What technologies are appropriate for a human workflow system?

  - by CCw

  I'm researching various workflow architectures and it is overwhelming. The workflow system I am creating will be almost completely human-driven. Very little, if any, asynchronous activity will be taking place. One possibility is to simply use a RDBMS and have a task table, from which stored procedures would be used to enforce synchronous access to each task. This seems very simple, but I'm having a hard time coming up with reasons why I might need to involve a heavier solution. If my system has ~500 concurrent users, and there is very little in the way of automated or asynchronous tasks, should I even consider the various workflow patterns/packages out there like Mule, BPEL/SOA, Spring Work Flow, etc?

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• Why doesn't Perl threading work when I call readdir beforehand?

  - by Kevin

  Whenever I call readdir before I create a thread, I get an error that looks like this: perl(2820,0x7fff70c33ca0) malloc: * error for object 0x10082e600: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug Abort trap What's strange is that it happens when I call readdir before I create a thread (i.e. readdir is not called in any concurrent code). I don't even use the results from readdir, just making the call to it seems to screw things up. When I get rid of it, things seem to work fine. Some example code is below: opendir(DIR, $someDir); my @allFiles = readdir(DIR); close(DIR); my $thread = threads-create(\&sub1); $thread-join(); sub sub1 { print "in thread\n" }

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• Programming error in Java Socket

  - by Akhil K Nambiar

  Can you tell me what is the error in this code? Socket socket = new Socket(hostname, port); PrintWriter out = new PrintWriter(socket.getOutputStream(), true); //DataInputStream is = new DataInputStream(socket.getInputStream()); out.println("hi"); System.out.print(in.readLine()); The Server Socket program is written in .Net and it echoes back the data. The data is sent successfully but could not be retrieved properly. I tried the same by using the linux command nc 192.168.1.6 8425 (enter) Hi (Sent data) Hi (recieved data) When I checked the code the data is found to have sent as byteStream in .Net. Is that a problem. In that case what modification should I make.

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• Understanding Clojure concurrency example

  - by dusha

  Hello, I just go through various documentation on Clojure concurrency and came accross the example on the website (http://clojure.org/concurrent_programming). (import '(java.util.concurrent Executors)) (defn test-stm [nitems nthreads niters] (let [refs (map ref (replicate nitems 0)) pool (Executors/newFixedThreadPool nthreads) tasks (map (fn [t] (fn [] (dotimes [n niters] (dosync (doseq [r refs] (alter r + 1 t)))))) (range nthreads))] (doseq [future (.invokeAll pool tasks)] (.get future)) (.shutdown pool) (map deref refs))) I understand what it does and how it works, but I don't get why the second anonymous function fn[] is needed? Many thanks, dusha. P.S. Without this second fn [] I get NullPointerException.

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• how to pass session variable to model in RoR?

  - by siulamvictor

  I used a global variable in my app for passing information before. But I got a problem and thanks everyone here suggested me to store those data in session with database. I tried, but I found that I can't access the session variable in Model. I googled and knew this is the Model normal behavior, RoR won't pass the session variable to Model. So how to pass the value of the session variable into Models? or is there any other method for my use case? I need a variable storing a value, which is required in all MVCs, and should be independent between different concurrent users. Thanks everyone. :)

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• PHP Possible Memory Leak

  - by dropson

  I have a script that loops through a database for images to convert with gd & imagick. I unset or replace all variables and objects in between each loop. For each loop, get_memory_usage(1) reveals a concurrent amount of memory used by that script. Which is expected. But, when I run "top", the %MEM column reports that this script, (same PID), increments with several percentages for each loop. I destroy all images when I'm done with them, and when I run get_defined_vars(); only the standard globals and a few variables I have is set. Why is "top" % Memory Usage different than what PHP reports? After 10 loops, PHP has taken 20% percetage of the system memory. I run php 5.2.6 on Debian 5

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• MySQL customized join query using multiple tables

  - by itgeek

  I am searching one student from each class from one group. There are different class groups and every group has different classes and every class has multiple students. See below: Group1 --> Class1, Class2 etc Class1 --> GreenStudent1, GreenStudent2 etc Class2 --> RedStudent1, RedStudent2 etc ------------------------------------------------------ SELECT table1.id, table1.myname, table1.marks table2.studentid, table2.studentname FROM table1 INNER JOIN table3 ON table1.oldid = table3.id INNER JOIN table2 ON table2.studentid = table3.newid WHERE table1.classgroup = 'SCI79' GROUP BY table1.oldid ORDER BY table1.marks DESC There are different joins applied in the query. Above mentioned query giving me correct results but I need little modification in it. Current query returning me one student from each class. What I need? I need one student from each class but only that student who has MAXIMUM table1.marks So I should have one student from each class who has maximum number in their relevant classes. Can anyone suggest some solution or rewrite this query? Thanks :)

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• Which one is better apporach comet or ajax?

  - by Rajesh Rolen- DotNet Developer

  i need to update client on any changes occurred on server. for that i found 2 approach. 1. using ajax which is also known as reverse ajax for this purpose. 2. using COMET. but i don't know exact difference in both. my site contains news content and i want that news to be automatically updates when new news is entered by my CMS application. i have got hundreds of concurrent users on my web application. please suggest me which approach should i use to get best solution. also please provide me good example's like for that so that i can implement it. NOTE: i am using .net framework 2.0 but if its not possible in 2.0 then can also move to 3.5 Thanks.

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• how to add language support to android

  - by avar

  hello i hope someone put me on the right direction with my problem i want to work on supporting my language, specially the writing on android we use Arabic characters with little modification ( like parsi, urdu etc).. i was hoping android has fully supported Arabic , then i would make changes to work with my language. but even 2.2 dosn't support Arabic . it just show Arabic characters and it is not connected. that is "????? " is displayed "? ? ? ? ?". some individuals have made Arabic support on CyanogenMod ROM's for some HTC phones, but they would not tell how they made it. I'v got the android source code, i want to know where to start, where to make changes , what is the library that handle fonts , shaping engine etc .. ps : android.com and other android related google groups are blocked in my country.

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• jQuery UI - Accordion Display issues

  - by Dave Kiss

  My accordion is working properly, but I'm having a few CSS and JS issues that are prohibiting it from displaying correctly. http://jsfiddle.net/frEWQ/ The JS is applying .ui-corners-all to the H3 before the "kwick" div below it has finished collapsing, giving an odd cut-off border during the animation The margin-bottom applied to the "kwick" div to give spacing between each tab disappears when the tab is set to display:none, getting rid of the spacing... but I can't apply the margin-bottom to the header because it disconnects the header from the "kwick" div below it. Any suggestions? Modification to the JS/CSS? Thanks

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• Multiple calculations on the same set of data: ruby or database?

  - by Pierre

  Hi, I have a model Transaction for which I need to display the results of many calculations on many fields for a subset of transactions. I've seen 2 ways to do it, but am not sure which is the best. I'm after the one that will have the least impact in terms of performance when data set grows and number of concurrent users increases. data[:total_before] = Transaction.where(xxx).sum(:amount_before) data[:total_after] = Transaction.where(xxx).sum(:amount_after) ... or transactions = Transaction.where(xxx) data[:total_before]= transactions.inject(0) {|s, e| s + e.amount_before } data[:total_after]= transactions.inject(0) {|s, e| s + e.amount_after } ... Which one should I choose? (or is there a 3rd, better way?) Thanks, P.

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• How to handle recurring execution?

  - by ShaneC

  I am trying to validate the solution I came up for what I think is a fairly typical problem. I have a service running and every 10 minutes it should do something. I've ended up with the following: private bool isRunning = true; public void Execute() { while(isRunning) { if(isRunning) { DoSomething(); m_AutoResetEvent.WaitOne(new Timespan(0, 10, 0)); } } } public void Stop() { isRunning = false; m_AutoResetEvent.Set(); } The immediate potential problems I can see is that I'm not doing any sort of locking around the isRunning modification in Stop() which gets called by another thread but I'm not sure I really need to? The worst that I think could happen is that it runs one extra cycle. Beyond that are there any obvious problems with this code? Is there a better way to solve this problem that I'm unaware of?

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• windows control library in c sharp

  - by apals

  I have just added a textbox, button, label to validate ID of 12 characters. The library is called check_ID. It works fine. The only problem is i have to access the forecolor of label, backcolor of textbox , forecolor of button as per color scheme of the project. But it seems that none of the properties of the objects in check_ID are available for modification. I have even changed the modifier to public of all objects by repoening the check_ID project. Is there another way to access the properties of these objects that are created using windows control library?. A very big thanks in advance.

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• gsub! Is modifying unspecified strings

  - by user335729

  I'm extracting some information from an XML file, and I want to perform some modifications on the data while keeping a copy of the original in a variable "origFile". This is what I have: require "rexml/document" include REXML doc = Document.new File.new(thePath) root = doc.root array = [] root.elements.each("dict/string") {|element| array << element} origFile = [] root.elements.each("dict"){|i| origFile << i} theBody = array[6][0].to_s theBody.gsub!(/\&lt;!-- more --\&gt;/, "----------Read More----------") The problem is that after I perform gsub! on theBody, origFile also has the modification. I don't understand why this would be or how to fix it. I would really appreciate your help.

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• Find maximum number of logged on users in SQL

  - by lleto

  Hi, I want to keep tabs on the number of concurrent users of my application. I therefore log a time_start and a time_stop. If I now want to query the database for the maximum number of logged on users and return the start date, how would I do that. The table looks like this: id | time_start | time_stop ----+---------------------+--------------------- 1 | 2010-03-07 05:40:59 | 2010-03-07 05:41:33 2 | 2010-03-07 06:50:51 | 2010-03-07 10:50:51 3 | 2010-02-21 05:20:00 | 2010-03-07 12:23:44 4 | 2010-02-19 08:21:12 | 2010-03-07 12:37:28 5 | 2010-02-13 05:52:13 | Where time_stop is empty the user is still logged on. In this case I would expect to see 2010-03-07 returned, since all users (5) were logged on at that moment. However if I would run the query with 'where time_start BETWEEN '2010-02-17' AND '2010-02-23' I would expect to see 2010-02-21 with a maximum of 2. Is this possible direct in SQL (using postgres) or do I need to parse the results in PHP? Thanks, lleto

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• Force close Android application Phone.apk in landscape mode

  - by user1277086

  Standard Android application Phone.apk with an outgoing call on the tenth of a second can use the landscape screen mode, but if you make a modification of graphic resources, in landscape mode the phone is closed with an error, Eclipse shows it - E / AndroidRuntime (2888): java.lang.RuntimeException: Unable to start activity ComponentInfo {com.android.phone / com.android.phone.InCallScreen}: java.lang.ClassCastException: android.view.AbsSavedState $ 1. I tried to set the AndroidManifest.xml setting [android: screenOrientation = "portrait"] of the article "Force an android activity to always use landscape mode" - the application falls. What can I try to do more? I tried to add a variable to a string android:screenOrientation="portrait" in decompiled Phone.apk on the and

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