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• Preventing concurrent data modification in Web based app

  - by Manoj

  Hi, I am building a web app in Silverlight which allows users to view and edit a database. In order to prevent multiple users from editing the same data, I was thinking of implementing a lock and key mechanism, so that other users are made to wait when one particular user is editing the data. Is there any way in which we can have variable(flag specifying if a user is editing data) in the server which can be shared across multiple clients? Is there a better way to manage this type of conurrent data access issues?

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• Java/C++ communication via pipe on Windows

  - by Warlax

  Hi, I have two separate programs, one in Java and one in C++, both running on Windows. We need to do bidirectional interprocess communication between the two. Up until now, we were using this awkward solution of writing to text files and reading them on the other side, where the producer would generate a .lock file when it's done writing and the consumer would remove that when it's done reading... like I said, awkward. If we were on *nix, we would use a pipe using popen() on the C++ and RadomAccessFile on the Java side. It seems to work well. What can we do on Windows? Can we use named pipes? Thank you.

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• What does MySqlDataAdapter.Fill return when the results are empty?

  - by Brian

  I have a 'worker' function that will be processing any and all sql queries in my program. I will need to execute queries that return result sets and ones that just execute stored procedures without any results. Is this possible with MySqlDataAdapter.Fill or do I need to use the MySqlCommand.ExecuteNonQuery() method? Here is my 'worker' function for reference: private DataSet RunQuery(string SQL) { MySqlConnection connection; MySqlCommand command; MySqlDataAdapter adapter; DataSet dataset = new DataSet(); lock(locker) { connection = new MySqlConnection(MyConString); command = new MySqlCommand(); command = connection.CreateCommand(); command.CommandText = SQL; adapter = new MySqlDataAdapter(); adapter.Fill(dataset); } return dataset; }

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• Multiple Producers Single Consumer Queue

  - by Talguy

  I am new to multithreading and have designed a program that receives data from two microcontroller measuring various temperatures (Ambient and Water) and draws the data to the screen. Right now the program is singly threaded and its performance SUCKS A BIG ONE. I get basic design approaches with multithreading but not well enough to create a thread to do a task but what I don't get is how to get threads to perform seperate task and place the data into a shared data pool. I figured that I need to make a queue that has one consumer and multiple producers (would like to use std::queue). I have seen some code on the gtkmm threading docs that show a single Con/Pro queue and they would lock the queue object produce data and signal the sleeping thread that it is finished then the producer would sleep. For what I need would I need to sleep a thread, would there be data conflicts if i didn't sleep any of the threads, and would sleeping a thread cause a data signifcant data delay (I need realtime data to be drawn 30 frames a sec) How would I go about coding such a queue using the gtkmm/glibmm library.

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• Securing files on IPhone

  - by clearbrian

  Hi Is there a way to decompile the binary from an IPhone app. I jailbroke my IPhone and was surprised to find other app's dbs wide open to be copied. So I exported my most important table and hardcoded it into code. Instead of loading table into array from a db I just generated code to fill the array and kept only the most basic DB info so relationships still work. Took a while but now works fine. I was just wondering am I safe, could someone decompile the binary for the app easily and extract the data. In Java its easy to decompile *.class files though thats bytecode where I presume iphone apps are more low level. I know IPhone sdk 4 can mark files as secure. Anyone know can this be overridden by jailbreaks or is this an unix lock?

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• Need help writing a recurring task scheduler.

  - by Sisiutl

  I need to write a tool that will run a recurring task on a user configurable schedule. I'll write it in C# 3.5 and it will run on XP, Windows 7, or Windows Server 2008. The tasks take about 20 minutes to complete. The users will probably want to set up several configurations: e.g, daily, weekly, and monthly cycles. Using Task Scheduler is not an option. The user will schedule recurrences through an interface similar to Outlook's recurring appointment dialog. Once they set up the schedule they will start it up and it should sit in the system tray and kick off its tasks at the appointed times, then send mail to indicate it has finished. What is the best way to write this so that it doesn't eat up resources, lock up the host, or otherwise misbehave?

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• Zend - Deny access to CSS, JS, Image files

  - by Vincent

  All, I have the following Zend application structure: helloworld - application - configs - controllers - models - layouts - include - library - public - design -- css -- site.css -- js -- global.js -- images -- siteheader.gif -- sitefooter.gif - .htaccess - index.php My .htaccess file in public folder looks like this: Options -MultiViews RewriteEngine On RewriteCond %{REQUEST_FILENAME} -s [OR] RewriteCond %{REQUEST_FILENAME} -l [OR] RewriteCond %{REQUEST_FILENAME} -d RewriteRule ^.*$ - [NC,L] RewriteRule ^.*$ index.php [NC,L] My document root points to the "public" folder. Currently, if the user visits a directory level URL, (Ex: http://localhost/design or localhost/css) , my .htaccess file above make sure to show him the "Access Forbidden" page. But if he visits the file level URL, (Ex: http://localhost/design/css/site.css), it shows him the CSS file or the js file or PHP file.. How can I make sure to lock file level access for the above file types, if accessed directly from the URL? Since my application is JS intensive, I want to protect it from users looking at it. Thanks

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• Error(2,7): PLS-00428: an INTO clause is expected in this SELECT statement

  - by omgzor

  I'm trying to create this trigger and getting the following compiler errors: create or replace TRIGGER RESTAR_PLAZAS AFTER INSERT ON PLAN_VUELO BEGIN SELECT F.NRO_VUELO, M.CAPACIDAD, M.CAPACIDAD - COALESCE(( SELECT count(*) FROM PLAN_VUELO P WHERE P.NRO_VUELO = F.NRO_VUELO ), 0) as PLAZAS_DISPONIBLES FROM VUELO F INNER JOIN MODELO M ON M.ID = F.CODIGO_AVION; END RESTAR_PLAZAS; Error(2,7): PL/SQL: SQL Statement ignored Error(8,5): PL/SQL: ORA-00933: SQL command not properly ended Error(8,27): PLS-00103: Encountered the symbol "end-of-file" when expecting one of the following: begin case declare end exception exit for goto if loop mod null pragma raise return select update while with <an identifier> <a double-quoted delimited-identifier> <a bind variable> << close current delete fetch lock insert open rollback savepoint set sql execute commit forall merge pipe Error(2,1): PLS-00428: an INTO clause is expected in this SELECT statement What's wrong with this trigger?

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• Best way to identify and dispose locked thread in java.

  - by Bala R

  I have to call a function 3rd party module on a new thread. From what I've seen, the call either completes quickly if everything went well or it just hangs for ever locking up the thread. What's a good way to start the thread and make the call and wait for a few secs and if the thread is still alive, then assuming it's locked up, kill (or stop or abandon) the thread without using any deprecated methods. I have something like this for now, but I'm not sure if this is the best way to do it and I want to avoid calling Thread.stop() as it's deprecated. Thanks. private void foo() throws Exception { Runnable runnable = new Runnable() { @Override public void run() { // stuff that could potentially lock up the thread. } }; Thread thread; thread = new Thread(runnable); thread.start(); thread.join(3500); if (thread.isAlive()) { thread.stop(); throw new Exception(); } }

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• Could not find generator mini_test:install

  - by David James

  I expected these generators to be available: $ rails g Usage: rails generate GENERATOR [args] [options] MiniTest: mini_test:controller mini_test:helper mini_test:install mini_test:mailer mini_test:model mini_test:scaffold So I ran: $ rails g mini_test:install But got this error: Could not find generator mini_test:install. As for my environment, here is the relevant portion of my Gemfile: group :test, :development do gem 'minitest-rails' end And the resulting portions of my Gemfile.lock: minitest (2.12.1) minitest-rails (0.0.7) minitest (~> 2.12) rails (~> 3.1) I am now in the process of debugging this. I would appreciate any tips. In any case, I will report back.

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• how to configure hibernate not to update @Version on each access to entity

  - by radai

  i have a simple query that returns an entity, and when i look at hibernate SQL output i see that when i execute this query hibernate updates the @Version field (on each consecutive read the @version field is updated). i dont modify anything in the entity i fetch, and i dont pass is as an argument to either persist or merge. this effectively means every read i make turns into a read+write. i've tried setting the lock mode t oboth NONE (jpa 2) and READ (jpa 1) to no avail. is there any way to achieve this? if so, is there any way to set this as the default behavior in persistence.xml in some way ? im using jpa2 over hibernate 3.6

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• How can I modify an Android bitmap in C++ (JNI/NDK) so that I can use on the Java side?

  - by HardCoder

  I call a C++ function over JNI and pass a RGBA_8888 bitmap, lock it, change the values, unlock it, return and then display it in Java with this C++ code: AndroidBitmap_getInfo(env, map, &info) < 0); AndroidBitmap_lockPixels(env, map, (void**)&pixel); for(i=info.width*info.height-1;i>=0;i--) { pixel[i] = 0xf1f1f1f1; } AndroidBitmap_unlockPixels(env, map); The problem I have is that the bitmaps looks not as I expect it and the pixel values (verified with getPixel) are not the same when I check them in Java from what I set them in C++. When I set the bitmap values to 0xffffffff I get the correct value in Java, but for many others I don't. 0xf1f1f1f1 for example turns into 0xF1FFFFFF. What do I have to do to make it work ? PS: I am using Android 2.3.4

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• Help me understand Dispose() implementation code from MSDN

  - by Benny

  the following code is from MSDN: Idisposable pattern protected virtual void Dispose(bool disposing) { // If you need thread safety, use a lock around these // operations, as well as in your methods that use the resource. if (!_disposed) { if (disposing) { if (_resource != null) _resource.Dispose(); Console.WriteLine("Object disposed."); } // Indicate that the instance has been disposed. _resource = null; _disposed = true; } } why the following statement: _resource = null; _disposed = true; are not enclosed by if (disposing) statement block? for me i would probably write like this: if (disposing) { if (_resource != null) { _resource.Dispose(); _resource = null; _disposed = true; } Console.WriteLine("Object disposed."); } anything wrong with my version?

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• How can I test whether a csv file is currently open and being written to - the file, not a file hand

  - by Henry

  I've seen a few questions/answers here that deal with this, but none really give me an answer/solution. I've got a Clipper system writing csv files to a Windows directory. I have a perl script running on a Linux server that is reading a mount of that Windows directory and importing the files to a database. Right now we're using flag files to indicate when a csv is no longer being written to; the flag files gets written after the csv is done. I'd really rather just get what I need from the csv itself, but I can't seem to find a way to tell when the file is open and being written to. lsof doesn't seem to answer my need. I've tried using flock and open the file with an exclusive lock, thinking it might throw an error if the file is being modified, but it doesn't. Any thoughts?

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• Do we need Record Level Locking when we already have Transaction for online ordering? (of concert ti

  - by Jian Lin

  For online ordering of concert seat or airline ticket, do we need Record Level Locking or is Transaction good enough? For concert ticket (say, seat Number 20B), or airline ticket (even with overbooking, the limit is 210, for example), I think the website cannot lock any record or begin transaction when showing the ticket purchase screen. But after the user clicks "Confirm Purchase", then the server should Begin a Transaction, Purchase Seat Number 20B, and try to Commit. If another user already bought Seat 20B in a previous transaction, then it is the "Commit" part that the current transaction will fail? So... we don't need Record Level Locking? Do Transactions always go serialized (one after another), so that's why we can know for sure there is no "race condition"? In what situation is Record Level Locking needed then?

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• Is passing a Command object/Reader to a function a good idea?

  - by Cyril Gupta

  I've been getting some inexplicable errors (running out of connections from the connection pool) with MySql database with .Net 4 (C#). Till now all my attempts at finding a reason for this have been in vain. Now I also have a situation in which a lock on a table is not cleared for a long time even though all I have been doing is read operations from it. My code looks okay (I've put all readers and connections in using blocks). The only anomaly I have is that I've been passing MySqlCommand and MySqlDataReader objects as parameters to functions who work with them. That doesn't seem like a bad idea for me because it avoids some repetition (DRY!). But since I can't find any other explanation I have to suspect that this is causing the problem. What do you think?

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• Queue access to the database to avoid multiple cache items

  - by MikeJ

  I have a music related ASP.NET web site which caches a lot of static information from the database on the first request. Sometimes, the application is reset and cache is cleared while the application is on heavy load and then all http requests go to the database to retrieve that static data and cache it for other requests. How can I ensure that only one request go to the database and cache the results, so that other request simply read that info from cache and not needlessly retrieve the same info over and over again. Can I use thread locking? For example, can I do something like lock(this) { db access here }?

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• I'm having a problem redeploying an applications using Drools and Tomcat 6

  - by FrankL

  I have a spring application that uses JBoss Drools 5. It works fine except for when I attempt to redeploy (i.e. hot deploy) the application after I make a change during development. It appears that tomcat keeps a lock on 2 drools jar files, drools-compiler-5.0.1.jar and drools-core-5.0.1.jar. Since they can't be deleted the new war file does not get deployed. If my application does not make any Drools logic calls, then the hot deploy works. Does anyone have any ideas?

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• Formatting Field Declarations in Eclipse

  - by geeko

  Greetings Overflowers, Problem: public abstract class Filter { private long id; protected String expression; } how can I align fields automatically in Eclipse, such in: public abstract class Filter { private long id; protected String expression; } Note the space before long, thank you ! UPDATE: I cannot find a customization option to align types of class members (e.g.: long and String) under Eclipse formatter options. Yes, there is one to align names of class members (e.g.: id and expression) but not their types. Please, take a lock at this issue in my examples above. Any solution ?

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• How to synchronize static method in java.

  - by Summer_More_More_Tea

  Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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• How to buffer stdout in memory and write it from a dedicated thread

  - by NickB

  I have a C application with many worker threads. It is essential that these do not block so where the worker threads need to write to a file on disk, I have them write to a circular buffer in memory, and then have a dedicated thread for writing that buffer to disk. The worker threads do not block any more. The dedicated thread can safely block while writing to disk without affecting the worker threads (it does not hold a lock while writing to disk). My memory buffer is tuned to be sufficiently large that the writer thread can keep up. This all works great. My question is, how do I implement something similar for stdout? I could macro printf() to write into a memory buffer, but I don't have control over all the code that might write to stdout (some of it is in third-party libraries). Thoughts? NickB

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• TFS Continuous Developement major project update

  - by mamu

  We are using TFS Continuous Development model Main Trunk - Various Development branches - Various Release branches All merging back to main trunk Now we need some major changes to our folder structure and solutions How do you handle folder restructure in above model of TFS usage? do i need to draw line and create new structure from latest Main trunk and lock all branches and do updates then creates branches with restructured new trunk. Or am i underestimating TFS, would be able to handle major folder structure updates and propagate over to branches. As long as i know if we move around folders in branch or trunk it don't like it.

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• How does Photoshop (Or drawing programs) blit?

  - by user146780

  I'm getting ready to make a drawing application in Windows. I'm just wondering, do drawing programs have a memory bitmap which they lock, then set each pixel, then blit? I don't understand how Photoshop can move entire layers without lag or flicker without using hardware acceleration. Also in a program like Expression Design, I could have 200 shapes and move them around all at once with no lag. I'm really wondering how this can be done without GPU help. I don't think super efficient algorithms could justify that? Thanks

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• How to maipulate the shell output in php

  - by Mirage

  I am trying to write php script which does some shell functions like reporting. So i am starting with diskusage report I want in following format drive path ------------total-size --------free-space Nothing else My script is $output = shell_exec('df -h -T'); echo "<pre>$output</pre>"; and its ouput is like below Filesystem Type Size Used Avail Use% Mounted on /dev/sda6 ext3 92G 6.6G 81G 8% / none devtmpfs 3.9G 216K 3.9G 1% /dev none tmpfs 4.0G 176K 4.0G 1% /dev/shm none tmpfs 4.0G 1.1M 4.0G 1% /var/run none tmpfs 4.0G 0 4.0G 0% /var/lock none tmpfs 4.0G 0 4.0G 0% /lib/init/rw /dev/sdb1 ext3 459G 232G 204G 54% /media/Server /dev/sdb2 fuseblk 466G 254G 212G 55% /media/BACKUPS /dev/sda5 fuseblk 738G 243G 495G 33% /media/virtual_machines How can i convert that ouput into my forn\matted output

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• Should I make my MutexLock volatile?

  - by sje397

  I have some code in a function that goes something like this: void foo() { { // scope the locker MutexLocker locker(&mutex); // do some stuff.. } bar(); } The function call bar() also locks the mutex. I am having an issue whereby the program crashes (for someone else, who has not as yet provided a stack trace or more details) unless the mutex lock inside bar is disabled. Is it possible that some optimization is messing around with the way I have scoped the locker instance, and if so, would making it volatile fix it? Is that a bad idea? Thanks.

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