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• C++ compiler structures such as Virtual method Table etc

  - by Roger

  I am aware of the C++ Virtual Table which allows dynamic dispatch for doing things at runtime (although if I am honest I am not completely sure of the full list of things it achieves). I am wondering what other "low level" aspects of C++ are there, which one doesnt usually come across when learning the C++ language? Things like: -How is multithreading and locking on objects performed? -Overloading/overwriting functions -Generics Are there other "structures", similar to the vtable, which assist with these types of things on a lower level? (and if anyone can help with what the VTable actually does it would be most appreciated!)

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• How to find out which process actually locks your dll when SharePoint Solution deployment failed

  - by ybbest

  When your SharePoint Solution package include third party or external dlls , you will often see your solution fail to deploy due to the locking of the dlls. Today I will show you how to find which process locks your dlls using Process Explorer. 1. Here is an example that your solution fails to deploy due to dll being locked. 2. Start the explorer by double click the procexp.exe 3. From the find tab click Find Handle or DLL 4.Type the your dll name and click Search 5. I can see all the processes that use my dlls at the moment, it looks like the iis , visual studio and SharePoint timer services might be the trouble. From my experience , it could be Visual studio. 6. Close visual studio and redeploy my solution, it works like charm. Re-search the dll, you can see Visual studio is not in the results.

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• hotkeys do not work sometimes in ubuntu 12.04

  - by stepank

  I use Ubuntu 12.04 with Unity 2D and I've stumbled upon this issue: sometimes shortcut keys stop working in some windows. For instance, I have these windows opened usually: Google Chrome, Terminal, Skype, Pidgin. Sometimes everything is OK and shortcuts work no matter what window I hit them from, however, hotkeys hit from Skype (more often) or Pidgin (less often) do not work, but they still work from Terminal or Google Chrome. Moreover, not all hotkeys are affected, the problem holds only for locking the computer (Ctrl + Alt + L) and other custom shortcuts like executing some command or launching a program (I used zenity --entry with [Super | Ctrl] + [some letter: K, N, etc] for testing). Does anyone have a clue what is causing the problem and how to fix it?

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• Ubuntu 12.04 freezing on startup

  - by Frank

  Have been looking everywhere to find a solution to this problem but have yet to find a solution. I am running 64 bit 12.04 LTS on a AMD C-50 Dual core 6 gigs ram AMD Ratheon HD 6250. The problem I am experiencing is when ubuntu gets to the wallpaper screen it will sometimes freeze soon after the the image appears or shortly there after gnome loads locking up keyboard and mouse. When I try to log in via the console the same thing happens (this is as ubuntu is loading). At the moment the system is set to auto login previously it was set to ask for password but it did the same thing. Switching to from lightdm to gdm did nothing to alleviate the issue. I have never had so many issues with ubuntu I have to say 12.04 is the most buggy version yet.

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• how to serialize function depending on what instance of object calls it, if same instance call in a thread then do serialize else not

  - by LondonDreams

  I have a function which fetches and updates some record from db and I am trying to make sure each if the function is called by same instance of object(same Or different thread) then function should behave synchronized else its a call from different object instance function need not to be synchronized. I have tried it use a lock per client. That is, instead of synchronizing the method directly using explicit locking through lock objects using Map. function is like :- getAndUpdateMyHitCount(myObjId){ //go to db and get unique record by myObjId //fetch value , increment , save update } And this function may get call is same thread by different Or same object instance But as fetching and matching from Map is slow , Is there other optimized way to do this ? Found similar at this Question but dont feel that is optimized

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• System crashed while upgrading, now unable to recover. Please help

  - by longloop

  Yesterday while upgrading from 11.4 to 11.10, due to power cut my system crashed. Ubuntu is unable to boot. While booting I get two options in grub, one is for recovery mode and the other is for normal ubuntu booting (and others are also thr for mem check and booting to windows). When I try to boot it normally, it pauses booting while displaying ' Checking battery statues' . Though i am not using a laptop, I am on a desktop. And In recovery mode the menu has 4 options - resume boot, fsck , remount and root ( to goto shell prompt) . If I go to shell and type ' apt-get dist upgrade' , it shows - W: not using locking for read only lock file /var/lib/dpkg/lock E:unable to write to /var/cache/apt E:The package lists or status files could not be parsed or opened. Please instruct me to recover from this situation.

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• Row Versioning Concurrency in SQL Server

  The optimistic concurrency model assumes that several concurrent transactions can usually complete without interfering with each other, and therefore do not require draconian locking on the resources they access. SQL Server 2005, and later, implements a form of this model called row versioning concurrency. It works by remembering the value of the data at the start of the transaction and checking that no other transaction has modified it before committing. If this optimism is justified for the pattern of activity within a database, it can improve performance by greatly reducing blocking. Kalen Delaney explains how it works in SQL Server.

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• Designing a hierarchical structure with lots of reads and writes?

  - by JD01

  I am in the process of working on a video on demand system part of it involves the management of a hierarchical tree structure (think windows explorer) which allows users to upload videos, move folders around, create new folders etc. User action will be allowed depending on which permissions they have. In addition to managing the structure (creating folders and uploading videos), subscribers will be viewing content (read access). The number of reads will be significantly more than the writes. My question (and it is big one) is should I store the data in a database (for the writes) and also have some sort of cache which will be used for the reads? or do I use two databases? or is there a better solution? Also I will have to resolve concurrency issues which I think optimistic locking on the database will resolve. I have a fair bit about CQRS over the last few months but not sure if this is the way to go. Any ideas?

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• Intel Wireless 4965AGN not achieving N throughput when connected to an Airport Express N network

  - by BenA

  I have an Intel Wireless WiFi Link 4965AGN adaptor in my laptop (HP Pavillion dv2000 series) which is connecting to a 5Ghz-only 802.11n network provided by an Apple Airport Express. The network is using WPA2 encryption. My desktop is also connected the Airport, via a Linksys WUSB600N USB adaptor. Both are running with the latest drivers, and the Airport is running the latest firmware. The Airport is also configured to use wide channels. The problem I have is that I never get throughput above 4MB/s when transferring files between the two machines. Even a pessimistic calculation shows a 270Mbps network as being capable of transfer rates at well above 10MB/s. I'm pretty sure I've isolated the issue to being the Intel adaptor, as wiring the desktop to the AP, and using the Linksys adaptor on the laptop immediately yielded speeds limited by the 100MB/s ethernet connection. I know that 802.11n is still a draft standard, and so mixing kit from different manufacturers can easily lead to poor results, but I was just wondering if anybody else out there has had success with this Intel adaptor on an N network? Or even better, connecting it to an Airport Express? Can anybody give me any advice on how to troubleshoot this issue? I should also mention that the Airport Express doesn't allow you to manually specify channels when running in N mode, and that I've been able to rule out interference from other Wireless LANs by scanning. There aren't any other 5GHz networks in my area. All ideas welcome! Update: A while later, I've just updated to the most recent drivers for both the Intel chip in the laptop, and the USB adaptor. Unfortunately this hasn't improved things :(. If anybody has any advice it would be be gratefully received.

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• .NET Reactor - How to Protect 64-bit Assemblies

  - by Cocowalla

  I have build 64-bit (x64) versions of some assemblies and am trying to obfuscate them with .NET Reactor, which claims to have 64-bit support. However, even if I disable all protection and locking options .NET Reactor is always producing 32-bit assemblies! Does anyone know how to get .NET Reactor to produce 64-bit assemblies?

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• How to secure a WCF service using NetNamedPipesBinding so that it can only be called by the current

  - by Samuel Jack

  I'm using a WCF service with the NetNamedPipesBinding to communicate between two AppDomains in my process. How do I secure the service so that it is not accessible to other users on the same machine? I have already taken the precaution of using a GUID in the Endpoint Address, so there's a little security through obscurity, but I'm looking for a way of locking the service down using ACL or something similar.

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• .net thread safety

  - by george9170

  Why is locking a type considered very bad? For example, lock(typeof(DateTime)) I understand that static methods of any class in .net is considered thread safe, and that instance members are not. So it isn't necessary to lock DateTime while you are using it. The book I am reading doesn't explain why it is bad it just says it is. Any explanation will be great.

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• RESTlet startup initialization deprecated?

  - by Chris Kaminski

  I'm trying to use the restlet.org library to build a RESTful web interface, and I've noticed that unlike it's servlet counterpart, it has no complement to GenericServlet.init(). Short of building another servlet to do my startup logic, is there any built-in way to avoid building my database factories and the like on the first request (and all the commensurate locking I'll have to do to avoid multiple initializations)?

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• How we can lock a table using PHP / Drupal

  - by Kamal Challa

  Hi iam developing a module in Drupal, which needs to have a locking machanism, When one user operating on form submission other should nt take action, How do i can achieve this in php/drupal iam using mysql database with MyISAM/INNODB Please help me Thanks in advance Kamal

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• Any XmlSerialization Limitations in WCF (as opposed to DataContract)?

  - by NealWalters

  Is there anything I might regret later, i.e. any major limitations if we choose XmlSerialization instead of DataContract? Until now, we have embraced the schema first contract design. For example, if we want to parameter inspection, security enhancements, etc... will locking in now with XmlSerialization be a problem when we try to add other WCF features?

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• How do I use SVN effectively?

  - by Tim Rogers

  I have an SVN repository that I've set up on my VPS, and I know all the basics (update, commit), but I don't know what all the other options mean. I am running TortoiseSVN on Windows (which is great!) and can see all these features like branching, locking, merging and patching! What do all these things mean? Is there anywhere with a good guide about how all the little bits and pieces in SVN work? Thanks, Tim

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• Block direct access to a file over http but allow php script access.

  - by Brandon G

  I'm loading my files (pdf, doc, flv, etc) into a buffer and serving them to my users with a script. I need my script to be able to access the file but not allow direct access to it. Whats the best way to achieve this? Should I be doing something with my permissions or locking out the directory with .htaccess?

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• Thread safety in Singleton

  - by Robert

  I understand that double locking in Java is broken, so what are the best ways to make Singletons Thread Safe in Java? The first thing that springs to my mind is: class Singleton{ private static Singleton instance; private Singleton(){} public static synchronized Singleton getInstance(){ if(instance == null) instance = new Singleton(); return instance; } } Does this work? if so, is it the best way (I guess that depends on circumstances, so stating when a particular technique is best, would be useful)

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• .htaccess query string with static page

  - by Wes

  So, unfortunately im using vBulletin with Kohana and my integration is getting a bit complicated locking vBulletin out. Doing some rewrites, this in particular RewriteCond %{QUERY_STRING} ^do=(editprofile|editoptions)$ RewriteRule ^forum/profile.php$ /user_profile/edit/ [R=301,L] Comes back with /user_profile/edit/?do=editprofile where I need /user_profile/edit/ Cheers, Wes

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• Why better isolation level means better performance in MS SQL Server

  - by Oleg Zhylin

  When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me READUNCOMMITTED - 409024 READCOMMITTED - 368021 REPEATABLEREAD - 358019 SERIALIZABLE - 348019 Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead.

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• May volatile be in user defined types to help writing thread-safe code

  - by David Rodríguez - dribeas

  I know, it has been made quite clear in a couple of questions/answers before, that volatile is related to the visible state of the c++ memory model and not to multithreading. On the other hand, this article by Alexandrescu uses the volatile keyword not as a runtime feature but rather as a compile time check to force the compiler into failing to accept code that could be not thread safe. In the article the keyword is used more like a required_thread_safety tag than the actual intended use of volatile. Is this (ab)use of volatile appropriate? What possible gotchas may be hidden in the approach? The first thing that comes to mind is added confusion: volatile is not related to thread safety, but by lack of a better tool I could accept it. Basic simplification of the article: If you declare a variable volatile, only volatile member methods can be called on it, so the compiler will block calling code to other methods. Declaring an std::vector instance as volatile will block all uses of the class. Adding a wrapper in the shape of a locking pointer that performs a const_cast to release the volatile requirement, any access through the locking pointer will be allowed. Stealing from the article: template <typename T> class LockingPtr { public: // Constructors/destructors LockingPtr(volatile T& obj, Mutex& mtx) : pObj_(const_cast<T*>(&obj)), pMtx_(&mtx) { mtx.Lock(); } ~LockingPtr() { pMtx_->Unlock(); } // Pointer behavior T& operator*() { return *pObj_; } T* operator->() { return pObj_; } private: T* pObj_; Mutex* pMtx_; LockingPtr(const LockingPtr&); LockingPtr& operator=(const LockingPtr&); }; class SyncBuf { public: void Thread1() { LockingPtr<BufT> lpBuf(buffer_, mtx_); BufT::iterator i = lpBuf->begin(); for (; i != lpBuf->end(); ++i) { // ... use *i ... } } void Thread2(); private: typedef vector<char> BufT; volatile BufT buffer_; Mutex mtx_; // controls access to buffer_ };

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• Mysql Replication

  - by ychian

  My current database design uses MyIsam mainly as the storage engine, I wonder if its possible to split some of the tables into MyIsam and some into Innodb in the same database. Reason of switching some of the tables to Innodb is because i need row-based locking which Innodb offers. I am not too sure whether this would have any effect on replication?

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• Concurrent update to DBF files with Advantage Local Sever and FoxPro

  - by ChrisR

  Is it safe to update DBF files using Advantage Local Server .Net provider whilst a FoxPro application is running that may also be accessing the DBF files? i.e. does Advantage take care of row locking?

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• Programmatically forward-lock an Android APK

  - by String

  Doing a bit of advance research, and am stuck on the point summarized in the title. Namely, is there any way to forward-lock an APK installed programmatically, from another app? I've not come across anything beyond a hint in the following post: http://groups.google.com/group/android-developers/msg/e39941389d4a4cf8 I can't see anything in the docs for PackageManager about forward- locking, but I readily confess that this is an unfamiliar area of the SDK for me. [Cross-posted with the Android-Developers Google group]

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• Virtual Cam - Cam Split .NET

  - by Fish

  I'm looking for a virtual webcam driver to use in a .NET project, this project will be GPL, and have no idea how many installations there will be The idea is that the application is using the webcam without locking the device. Found a couple of programs that do the job, but either in application and/or too expensive: * http://www.softservice.org/products_camsplitter.html (9.99$/installation) * splitcamera.com (program, no SDK available) All idea's are welcome

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