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• prevent race condition without using locks C++

  - by Hristo

  How do I prevent a race condition with locking or using mutexes/semaphors in C++? I'm dealing with a nested for loop in which I will be setting a value in an array: for (int i = 0; i < m; ++i) for (int j = 0; j < n; ++j) for (int k = 0; k < o; ++k) array[k] += foo(...); More or less, I want to deal with this so that I can ensure different threads running at the same time don't write to array[k] at the same time. Any suggestions on how to approach this? Thanks, Hristo

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• File Encrypt/Decrypt under load?

  - by chopps

  I found an interesting article about encrypting and decrypting files but since it uses a file.dat to store the key this will run into problems when theres alot of users on the site dealing with alot of files. http://www.codeproject.com/KB/security/VernamEncryption.aspx?display=Print Should a new file be created every time a file needs decrypting or would there be a better way to do this? UPDATE: Here is what im using to avoid the locking problems. using (Mutex FileLock = new Mutex(true, System.Guid.NewGuid().ToString())) { try { FileLock.WaitOne(); using (FileStream fs = new FileStream(keyFile, FileMode.Open)) { keyBytes = new byte[fs.Length]; fs.Read(keyBytes, 0, keyBytes.Length); } } catch (Exception ex) { EventLog.LogEvent(ex); } finally { FileLock.ReleaseMutex(); } } I tested it on 1000 TIFFs doing both encryption and decryption without any errors.

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• ASP.Net Architecture Specific to Shared/Static functions

  - by Maxim Gershkovich

  Hello All, Could someone please advise in the context of a ASP.Net application is a shared/static function common to all users? If for example you have a function Public shared function GetStockByID(StockID as Guid) as Stock Is that function common to all current users of your application? Or is the shared function only specific to the current user and shared in the context of ONLY that current user? So more specifically my question is this, besides database concurrency issues such as table locking do I need to concern myself with threading issues in shared functions in an ASP.Net application? In my head; let’s say my application namespace is MyTestApplicationNamespace. Everytime a new user connects to my site a new instance of the MyTestApplicationNamespace is created and therefore all shared functions are common to that instance and user but NOT common across multiple users. Is this correct?

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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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• How do I implement .net plugins without using AppDomains?

  - by Abtin Forouzandeh

  Problem statement: Implement a plug-in system that allows the associated assemblies to be overwritten (avoid file locking). In .Net, specific assemblies may not be unloaded, only entire AppDomains may be unloaded. I'm posting this because when I was trying to solve the problem, every solution made reference to using multiple AppDomains. Multiple AppDomains are very hard to implement correctly, even when architected at the start of a project. Also, AppDomains didn't work for me because I needed to transfer Type across domains as a setting for Speech Server worfklow's InvokeWorkflow activity. Unfortunately, sending a type across domains causes the assembly to be injected into the local AppDomain. Also, this is relevant to IIS. IIS has a Shadow Copy setting that allows an executing assembly to be overwritten while its loaded into memory. The problem is that (at least under XP, didnt test on production 2003 servers) when you programmatically load an assembly, the shadow copy doesnt work (because you are loading the DLL, not IIS).

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• Data access strategy for a site like SO - sorted SQL queries and simultaneous updates that affect th

  - by Kaleb Brasee

  I'm working on a Grails web app that would be similar in access patterns to StackOverflow or MyLifeIsAverage - users can vote on entries, and their votes are used to sort a list of entries based on the number of votes. Votes can be placed while the sorted select queries are being performed. Since the selects would lock a large portion of the table, it seems that normal transaction locking would cause updates to take forever (given enough traffic). Has anyone worked on an app with a data access pattern such as this, and if so, did you find a way to allow these updates and selects to happen more or less concurrently? Does anyone know how sites like SO approach this? My thought was to make the sorted selects dirty reads, since it is acceptable if they're not completely up to date all of the time. This is my only idea for possibly improving performance of these selects and updates, but I thought someone might know a better way.

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• MEMORY(HEAP) vs. InnoDB in a Read and Write Environment

  - by Johannes

  I want to program a real-time application using MySQL. It needs a small table (less than 10000 rows) that will be under heavy read (scan) and write (update and some insert/delete) load. I am really speaking of 10000 updates or selects per second. These statements will be executed on only a few (less than 10) open mysql connections. The table is small and does not contain any data that needs to be stored on disk. So I ask which is faster: InnoDB or MEMORY (HEAP)? My thoughts are: Both engines will probably serve SELECTs directly from memory, as even InnoDB will cache the whole table. What about the UPDATEs? (innodb_flush_log_at_trx_commit?) My main concern is the locking behavior: InnoDB row lock vs. MEMORY table lock. Will this present the bottleneck in the MEMORY implementation? Thanks for your thoughts!

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• Eval IronPython Scripts during ASP.NET Web Request; Static Engine or Not

  - by Josh Pearce

  I would like to create an ASP.NET MVC web application which has extensible logic that does not require a re-build. I was thinking of creating a filter which had an instance of the IronPython engine. What I would like to know is: how much overhead is there in creating a new engine during each web request, and would it be a better idea to keep a static engine around? However, if I were to keep a single static engine around, what are the issues I might run into as far as locking and script scope? Is it possible to have multiple scopes in the same IropPython engine so I don't get variable collision and security issues between web requests?

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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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• Do I have to use Stored Procedures to get query level security or can I still do this with Dynamic S

  - by Peter Smith

  I'm developing an application where I'm concerned about locking down access to the database. I know I can develop stored procedures (and with proper parameter checking) limit a database user to an exact set of queries to execute. It's imperative that no other queries other then the ones I created in the stored procedures be allowed to execute under that user. Ideally even if a hacker gained access to the database connection (which only accepts connections from certain computers) they would only be able to execute the predefined stored procedures. Must I choose stored procedures for this or can I use Dynamic Sql with these fine grain permissions?

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• MEMORY(HEAP) vs. InnoDB in a Read and Write Envirnment

  - by Johannes

  I want to programm a real-time application using MySQL. It needs a small table (less than 10000 rows) that will be under heavy read (scan) and write (update and some insert/delete) load. I am really speaking of 10000 updates or selects per second. These statements will be executed on only a few (less than 10) open mysql connections. The table is small and does not contain any data that needs to be stored on disk. So I ask which is faster: InnoDB or MEMORY (HEAP)? My thoughts are: Both enginges will probably serve SELECTs directly from memory, as even InnoDB will cache the whole table. What about the UPDATAEs? (innodb_flush_log_at_trx_commit?) My main concern is the locking behavior: InnoDB row lock vs. MEMORY table lock. Will this present the bottleneck in the MEMORY implementation? Thanks for your thoughts!

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• Is it immoral to put a captcha on a login form?

  - by azkotoki

  In a recent project I put a captcha test on a login form, in order to stop possible brute force attacks. The immediate reaction of other coworkers was a request to remove it, saying that it was inapropiate for that purpose, and that it was quite exotic to see a captcha in that place. I've seen captcha images on signup, contact, password recovery forms, etc. So I personally don't see inapropiate to put a captcha also on a place like that. Well, it obviously burns down usability a little bit, but it's a matter of time and getting used to it. With the lack of a captcha test, one would have to put some sort of blacklist / account locking mechanism, which also has some drawbacks. Is it a good choice for you? Am I getting somewhat captcha-aholic and need some sort of group therapy? Thanks in advance.

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• Sinatra: How do I provide access to a login form while preventing access to the rest of my Sinatra a

  - by Brandon Toone

  I recently created a Sinatra app with a login form (no basic auth). To prevent access to the app unless the user logged in I put a before block in place before do unless request.path_info == '/login' authenticated? end end I quickly realized that this prevented me from accessing resources in the public directory like my style sheet and logo unless authenticated first as well. To get around that I changed my filter to the following: before do unless request.path_info == '/login' || request.path_info == "/stylesheets/master.css" || request.path_info == "/images/logo.png" authenticated? end end If there were lots of resources I needed to provide exceptions to this way of making them would quickly become overwhelming. What is a better way to code this so I can make exceptions for the public directory or even its specific sub-directories and files like /stylesheets, /images, /images/bg.png but not /secret or /secret/eyes-only.pdf? Or ... Is there a completely different best-practice to handle this situation of locking down everything except the stuff related to logging in (handlers, views, resources)?

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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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• iphone singleton object synchronization

  - by user127091

  I'm working on an iphone app but this is probably a general question. I have a singleton Model class and there would be scenarios where multiple NSOperations (threads) would exist and work with the singleton object. If they all call the same method in this object, do i need to have some locking mechanism? Or can this method be executed only one at a time? I do not have a computer science background but my guess is that all threads would have their CALL to the same address (this method). Also can you please suggest a good beginner programming book that discusses general programming concepts. I don't have the brains for Knuth kinda books.

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• Floating Menu CSS/Javascript issues

  - by Ron Cassel

  I'm new to all this so thanks for being patient. Ok so I'm building a site with a Floating Javascript menu. The original code is from: Jtricks Absolute Floating Menu Here's the issue: When viewing the site in a mobile browser, zooming in initially caused the floating javascript menu to leave the far left of the page and cover content on the page. I fixed this by locking it into a fixed width div on the left side of the page. Now the issue I have is, I don't want the fancy animation of the javascript. A simple CSS script for a fixed window is fine. The only issue is, everything I've tried has done the same "free floating" thing when zoomed in on mobile browsers and I can't seem to find a fix. Anyone have any ideas?

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• (Windows) How to lock all applications (explorer, task manager etc.) and make only the browser activ

  - by Unni

  I'm trying to run only the browser in the system - locking access to everything else. Only the supervisor can resume the normal functioning of the system after giving a password. This kind of activity is usually done by virus. Disabling the registry for Task manager etc. Does anyone know of any source available that does this? I might be able to pull it off in Windows XP. But have anyone tried this in Windows 7 ? The aim is to to emulate the Chrome OS on Windows. Only the browser. Nothing else.

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• IIS Not working

  - by 3bd

  I have a web site that built on Visual studio 2008 and i need to run it from my computer (Win 7 Ultimate) as a server I tried to publish it to IIS and this is simply not working and i have the flowing error : Error Summary HTTP Error 500.19 - Internal Server Error The requested page cannot be accessed because the related configuration data for the page is invalid. Config Error This configuration section cannot be used at this path. This happens when the section is locked at a parent level. Locking is either by default (overrideModeDefault="Deny"), or set explicitly by a location tag with overrideMode="Deny" or the legacy allowOverride="false". any one can help?

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• Preventing dictionary attacks on a web application

  - by Kevin Pang

  What's the best way to prevent a dictionary attack? I've thought up several implementations but they all seem to have some flaw in them: Lock out a user after X failed login attempts. Problem: easy to turn into a denial of service attack, locking out many users in a short amount of time. Incrementally increase response time per failed login attempt on a username. Problem: dictionary attacks might use the same password but different usernames. Incrementally increase response time per failed login attempt from an IP address. Problem: easy to get around by spoofing IP address. Incrementally increase response time per failed login attempt within a session. Problem: easy to get around by creating a dictionary attack that fires up a new session on each attempt.

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• iphone threading speed up startup of app

  - by BahaiResearch.com

  I have an app that must get data from the Sqlite database in order to display the first element to the User. I have created a domain object which wraps the DB access and is a thread safe singleton. Is this following strategy optimal to ensure the fastest load given the iPhone's file access and memory management capabilities in threaded apps: 1) In the AppDelegate's FinishedLaunching event the very first thing I do is create the domain singleton within a new thread. This will cause the domain object to go to Sqlite and get the data it needs without locking the UI thread. 2) I then call the standard Window methods to add the View and MakeKeyAndVisible etc. Is there an earlier stage in the AppDelegate where I should fire off the thread that creates the Domain Object and accesses Sqlite?

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• Can I have fixed typed ArrayList in C#, just like C++?

  - by Kazoom

  I have an ArrayList which contains fixed type of objects. However everytime I need to extract an object a particular index, I need to typecast it to my user defined type from object type. Is there a way in C# to declare ArrayList of fixed types just like Java and C++, or is there a work around to avoid the typecasting everytime? Edit: I apologize I forgot mentioning that I require the datastructure to be thread-safe, which List is not. Otherwise I would have just used a normal Array. But I want to save myself from the effort of explicitly locking and unlocking while writing the array. So I thought of using ArrayList, synchronize it, but it requires typecasting every time.

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• How do I prevent race condition WITHOUT using locks in C++?

  - by Hristo

  How do I prevent a race condition WITHOUT locking or using mutexes/semaphors in C++? I'm dealing with a nested for loop in which I will be setting a value in an array: for (int i = 0; i < m; ++i) for (int j = 0; j < n; ++j) for (int k = 0; k < o; ++k) array[k] += foo(...); More or less, I want to deal with this so that I can ensure different threads running at the same time don't write to array[k] at the same time. Any suggestions on how to approach this? Edit: I am running on a Linux machine and I also have to use the Intel compiler. I will be using "icc" instead of "gcc" to compile the code.

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• How do I prevent Window resizing when the Workstation is Locked then Unlocked?

  - by Terry

  We have an application that is run in multi-monitor environments. Users normally have the application dialog spread out to span multiple mointors. If the user locks the workstation, and then unlocks it, our application is told to resize. Our users find this behavior frustrating, as they then spend some time restoring the previous layout. We're not yet sure whether it is the graphics driver requesting the resize or Windows. Hopefully through this question, it will become clearer which component is responsible, Popular applications like (File) Explorer and Firefox behave the same way in this setup. To replicate just: open Explorer (Win+E) drag the Explorer window to being horizontally larger than 1 screen lock workstation (Win+L), unlock the application should now resize to being solely on 1 screen How do I prevent Window resizing when the Workstation is Locked then Unlocked? Will we need to code in checks for (un)locking? Is there another mechanism we're not aware of?

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• How to show the animation without exposing the code?

  - by bonCodigo

  There's an animation done in jQuery within jsfiddle. I do not have a website as of now to "implant" it and share the URL. I also can't give the jsfiddle. So how can I share my animation to the audience without showing the code? Does github or any other facility tools allow locking the code and showing the final product without having a website, yet I could get a URL for the audience to view it? I regret for the rookie-question in this context as I am still new to web stuff. EDIT: jsFiddle shows 3 code windows along the results :html, css, js. My requirement is to only show the results window to the audience and by all means to hide codes and leads via URL to the codes. Ideal solution demands a results to be shown and URL that is encrypted (at best).

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