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  • Lock free multiple readers single writer

    - by dummzeuch
    I have got an in memory data structure that is read by multiple threads and written by only one thread. Currently I am using a critical section to make this access threadsafe. Unfortunately this has the effect of blocking readers even though only another reader is accessing it. There are two options to remedy this: use TMultiReadExclusiveWriteSynchronizer do away with any blocking by using a lock free approach For 2. I have got the following so far (any code that doesn't matter has been left out): type TDataManager = class private FAccessCount: integer; FData: TDataClass; public procedure Read(out _Some: integer; out _Data: double); procedure Write(_Some: integer; _Data: double); end; procedure TDataManager.Read(out _Some: integer; out _Data: double); var Data: TDAtaClass; begin InterlockedIncrement(FAccessCount); try // make sure we get both values from the same TDataClass instance Data := FData; // read the actual data _Some := Data.Some; _Data := Data.Data; finally InterlockedDecrement(FAccessCount); end; end; procedure TDataManager.Write(_Some: integer; _Data: double); var NewData: TDataClass; OldData: TDataClass; ReaderCount: integer; begin NewData := TDataClass.Create(_Some, _Data); InterlockedIncrement(FAccessCount); OldData := TDataClass(InterlockedExchange(integer(FData), integer(NewData)); // now FData points to the new instance but there might still be // readers that got the old one before we exchanged it. ReaderCount := InterlockedDecrement(FAccessCount); if ReaderCount = 0 then // no active readers, so we can safely free the old instance FreeAndNil(OldData) else begin /// here is the problem end; end; Unfortunately there is the small problem of getting rid of the OldData instance after it has been replaced. If no other thread is currently within the Read method (ReaderCount=0), it can safely be disposed and that's it. But what can I do if that's not the case? I could just store it until the next call and dispose it there, but Windows scheduling could in theory let a reader thread sleep while it is within the Read method and still has got a reference to OldData. If you see any other problem with the above code, please tell me about it. This is to be run on computers with multiple cores and the above methods are to be called very frequently. In case this matters: I am using Delphi 2007 with the builtin memory manager. I am aware that the memory manager probably enforces some lock anyway when creating a new class but I want to ignore that for the moment. Edit: It may not have been clear from the above: For the full lifetime of the TDataManager object there is only one thread that writes to the data, not several that might compete for write access. So this is a special case of MREW.

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  • free() on stack memory

    - by vidicon
    I'm supporting some c code on Solaris, and I've seen something weird at least I think it is: char new_login[64]; ... strcpy(new_login, (char *)login); ... free(new_login); My understanding is that since the variable is a local array the memory comes from the stack and does not need to be freed, and moreover since no malloc/calloc/realloc was used the behaviour is undefined. This is a real-time system so I think it is a waste of cycles. Am I missing something obvious?

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  • free RSS feed caching

    - by cherouvim
    Hello I've got an application which serves an rss feed of headlines and I need to provide this rss feed to other consumers. I don't want to provide the rss directly from my server though, due to limited server resources, so I need to proxy (cache) it through some service which will handle the load. Assuming the rss feed URL of my application is http://example.com/rss I initially provided my consumers with the url http://ajax.googleapis.com/ajax/services/feed/load?v=1.0&q=http%3A%2F%2Fexample.com%2Frss which solved my server load problem but introduced a liveness problem. The headlines are minutes to hours late from the actual feed (haven't exactly measured how much late). I've also tried distributing through feedburner so the url became something like http://feeds.feedburner.com/example123?format=xml but the liveness problem still exists. Is there a public and free solution for this problem? Anything below 5 minutes of liveness delay would be totally acceptable. thanks

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  • Free US sales-tax lookup (per zip etc.)?

    - by Shimmy
    I am creating a pricing program. I need to calculate the amounts according to the current tax list in the US (in various places). I want to have a button 'Update taxes' in the administrative settings of the application, so when the user clicks it, it should download from somewhere the active tax amounts. So I actually want to have a function decimal GetTax(string zip). Does anyone knows about a free downloadable xml, or RSS accessible or even a website that I can crawle in and get this info from?

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  • In WPF: Children.Remove or Children.Clear doesn't free objects

    - by Bart Roozendaal
    I create some UIElements from code behind and was anticipating the garbage collection to clear up stuff. However, the objects are not free-ed at the time I expected it. I was expecting them to be freeed at RemoveAt(0), but they are only freed at the end of the program. How can I make the objects be freed when removed from the Children collection of the Canvas? <Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Window1" Height="300" Width="300" MouseDown="Window_MouseDown"> <Grid> <Canvas x:Name="main" /> </Grid> </Window> The code behind is: public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } private void Window_MouseDown(object sender, MouseButtonEventArgs e) { if (main.Children.Count == 0) main.Children.Add(new MyControl() { Background = Brushes.Yellow, Width = 100, Height = 50 }); else main.Children.RemoveAt(0); } } public class MyControl : UserControl { ~MyControl() { Debug.WriteLine("Goodbye"); } }

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  • PHP - "Fat Free Framework" Find Methods and Showing Results in Template

    - by user1672808
    Just started trying the "Fat Free Framework" I'm building a site using a MySQL DB with 265 fields, and 5000+ rows in the DB; I can load() a specific record easily, no problems. When using find(), afind(), and even "select()", template will show blank lines or lines with "filler" text, with the correct number of rows for the query results, but no text/data from the DB itself; Same problem whether using objects or simply arrays from result (afind() and find()). I've copied/pasted the code verbatim from examples and from documentation, with only the DB specific items changed. Still, no luck. CODE IN PHP FILE (function from CLASS): static function home() { $featured=new Axon('boats'); $F3::set('boatlist',$featured->afind('D_CustomerID=173')); F3::set('content',TEMPLATE_DIR .'/home.html'); echo Template::serve(TEMPLATE_DIR .'/layout.html'); } TEMPLATE home.html: <div class="span8"> <h3> Featured Boats </h3> <F3:repeat group="{{@boatlist}}" value="{{@boat}}"> <div style="margin-left: 2em" class="thumbnails"> <p> <a href="boat/{{@boat['D_BoatNum']}}">{{trim(@boat['D_Description'])}}</a> by {{@boat['D_CustomerID']}} </p> <p> {{@boat['D_Price']}} </p> </div> </F3:repeat> </div> The number of rows this produces coincides with the correct number of rows in the DB. However, the actual data from each field does not show. Any ideas?

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  • Lock-Free Data Structures in C++ Compare and Swap Routine

    - by slf
    In this paper: Lock-Free Data Structures (pdf) the following "Compare and Swap" fundamental is shown: template <class T> bool CAS(T* addr, T exp, T val) { if (*addr == exp) { *addr = val; return true; } return false; } And then says The entire procedure is atomic But how is that so? Is it not possible that some other actor could change the value of addr between the if and the assignment? In which case, assuming all code is using this CAS fundamental, it would be found the next time something "expected" it to be a certain way, and it wasn't. However, that doesn't change the fact that it could happen, in which case, is it still atomic? What about the other actor returning true, even when it's changes were overwritten by this actor? If that can't possibly happen, then why? I want to believe the author, so what am I missing here? I am thinking it must be obvious. My apologies in advance if this seems trivial.

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  • Are you supposed to type '6' with the left hand or the right hand?

    - by Joey Adams
    A few weeks ago, I did a Google Images search for keyboard finger charts to see which fingers I'm supposed to be using to type which keys. According to the charts, '6' is supposed to be typed with the right hand: (as shown on en.wikipedia.org/wiki/Typing) However, today I spotted a split keyboard in a store with the '6' on the left side of the split. Indeed, an image search for split keyboards indicates that this is the norm: (as shown on en.wikipedia.org/wiki/Microsoft_Natural_keyboard) When doing touch typing "correctly", should I go with the finger charts (type 6 with my right hand), or should I go with the split keyboards (type 6 with my left hand)? <troll> Is this just another example of Microsoft not following the standards? </troll>

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  • Recommendations for a free GIS library supporting raster images

    - by gspr
    Hi. I'm quite new to the whole field of GIS, and I'm about to make a small program that essentially overlays GPS tracks on a map together with some other annotations. I primarily need to allow scanned (thus raster) maps (although it would be nice to support proper map formats and something like OpenStreetmap in the long run). My first exploratory program uses Qt's graphics view framework and overlays the GPS points by simply projecting them onto the tangent plane to the WGS84 ellipsoid at a calibration point. This gives half-decent accuracy, and actually looks good. But then I started wondering. To get the accuracy I need (i.e. remove the "half" in "half-decent"), I have to correct for the map projection. While the math is not a problem in itself, supporting many map projection feels like needless work. Even though a few projections would probably be enough, I started thinking about just using something like the PROJ.4 library to do my projections. But then, why not take it all the way? Perhaps I might aswell use a full-blown map library such as Mapnik (edit: Quantum GIS also looks very nice), which will probably pay off when I start to want even more fancy annotations or some other symptom of featuritis. So, finally, to the question: What would you do? Would you use a full-blown map library? If so, which one? Again, it's important that it supports using (and zooming in and out with) raster maps and has pretty overlay features. Or would you just keep it simple, and go with Qt's own graphics view framework together with something like PROJ.4 to handle the map projections? I appreciate any feedback! Some technicalities: I'm writing in C++ with a Qt-based GUI, so I'd prefer something that plays relatively nicely with those. Also, the library must be free software (as in FOSS), and at least decently cross-platform (GNU/Linux, Windows and Mac, at least). Edit: OK, it seems I didn't do quite enough research before asking this question. Both Quantum GIS and Mapnik seem very well suited for my purpose. The former especially so since it's based on Qt.

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  • Photoshop CS6 - spacebar shortcut for hand tool has stopped working

    - by Decavolt
    In Photoshop CS6, the default behavior of depressing the spacebar as a shortcut for the Hand tool was working as expected, then stopped for no apparent reason. I have rebooted, closed browsers, shut down all other applications and deleted preferences and the problem persists. The spacebar works properly elsewhere, including Photoshop CS4. Is there a keyboard shortcut setting I'm missing (I've checked Edit - Keyboard Shortcuts and can find nothing for the spacebar, and can not add it to the Hand tool). This is on OSX Lion 10.7.4

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  • Where can I find free and open data?

    - by kitsune
    Sooner or later, coders will feel the need to have access to "open data" in one of their projects, from knowing a city's zip to a more obscure information such as the axial tilt of Pluto. I know data.un.org which offers access to the UN's extensive array of databases that deal with human development and other socio-economic issues. The other usual suspects are NASA and the USGS for planetary data. There's an article at readwriteweb with more links. infochimps.org seems to stand out. Personally, I need to find historic commodity prices, stock values and other financial data. All these data sets seem to cost money however. Clarification To clarify, I'm interested in all kinds of open data, because sooner or later, I know I will be in a situation where I could need it. I will try to edit this answer and include the suggestions in a structured manners. A link for financial data was hidden in that readwriteweb article, doh! It's called opentick.com. Looks good so far! Update I stumbled over semantic data in another question of mine on here. There is opencyc ('the world's largest and most complete general knowledge base and commonsense reasoning engine'). A project called UMBEL provides a light-weight, distilled version of opencyc. Umbel has semantic data in rdf/owl/skos n3 syntax. The Worldbank also released a very nice API. It offers data from the last 50 years for about 200 countries

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  • Theory of computation - Using the pumping lemma for context free languages

    - by Tony
    I'm reviewing my notes for my course on theory of computation and I'm having trouble understanding how to complete a certain proof. Here is the question: A = {0^n 1^m 0^n | n>=1, m>=1} Prove that A is not regular. It's pretty obvious that the pumping lemma has to be used for this. So, we have |vy| = 1 |vxy| <= p (p being the pumping length, = 1) uv^ixy^iz exists in A for all i = 0 Trying to think of the correct string to choose seems a bit iffy for this. I was thinking 0^p 1^q 0^p, but I don't know if I can obscurely make a q, and since there is no bound on u, this could make things unruly.. So, how would one go about this?

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  • Where can one find free software icons / images?

    - by mmattax
    This may not be directly related to programming, but I always find it hard to get quality icons that can be used for software. I currently have the need for some type of "green checkmark image", and I always seem to be looking for print, save, delete types of icons... Anybody have good resources? Note: I rather not be stealing someone's intellectual property.

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  • Jquery's a FREE grid display

    - by mmcgrail
    I have been using Flesigrid for my CMS and I like it except there are some things I think it could do better like get the column headers from the ajax results rather then in the setup of the flexigrid or having the ability to change the buttons on reload things of that nature. I've been considering a mod of the plugin though I'm not sure i really want to do that. But the question is ... is there something that might be better that I somehow missed when I was looking for grid display ?

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  • Large free block of english non-pronoun text

    - by Tom
    As part of teaching myself python I've written a script which allows a user to play hangman. At the moment, the hangman word to be guessed is simply entered manually at the start of the script's code. I want instead for the script to choose randomly from a large list of english words. This I know how to do - my problem is finding that list of words to work from in the first place. Does anyone know of a source on the net for, say, 1000 common english words where they can be downloaded as a block of text or something similar that I can work with? (My initial thought was grabbing a chunk of a novel from project gutenburg [this project is only for my own amusement and won't be available anywhere else so copyright etc doesn't matter hugely to me btw], but anything like that is likely to contain too many names or non-standard words that wouldn't be suitable for hangman. I need text that only has words legal for use in scrabble, basically). It's a slightly odd question for here I suppose, but actually I thought the answer might be of use not just to me but anyone else working on a project for a wordgame or similar that needs a large seed list of words to work from. Many thanks for any links or suggestions :)

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  • Reminder: Totally Awesome and Totally Free Training SQL Server Training

    - by KKline
    One of the things that I enjoy about working for Quest Software is that we give back copiously to the community. From activities and offerings like SQLServerPedia , to our free posters mailed anywhere in North America (and don't forget the free hi-res PDFs for the rest of the world ), Don't forget that free DVDs of our virtual conferences featuring me, along with Buck Woody ( blog | twitter ) and Brent Ozar ( blog | twitter ) will be mailed anywhere in North America free of charge, now available...(read more)

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  • Free Document/Content Management System Using SharePoint 2010

    - by KunaalKapoor
    That’s right, it’s true. You can use the free version of SharePoint 2010 to meet your document and content management needs and even run your public facing website or an internal knowledge bank.  SharePoint Foundation 2010 is free. It may not have all the features that you get in the enterprise license but it still has enough to cater to your needs to build a document management system and replace age old file shares or folders. I’ve built a dozen content management sites for internal and public use exploiting SharePoint. There are hundreds of web content management systems out there (see CMS Matrix).  On one hand we have commercial platforms like SharePoint, SiteCore, and Ektron etc. which are the most frequently used and on the other hand there are free options like WordPress, Drupal, Joomla, and Plone etc. which are pretty common popular as well. But I would be very surprised if anyone was able to find a single CMS platform that is all things to all people. Infact not a lot of people consider SharePoint’s free version under the free CMS side but its high time organizations benefit from this. Through this blog post I wanted to present SharePoint Foundation as an option for running a FREE CMS platform. Even if you knew that there is a free version of SharePoint, what most people don’t realize is that SharePoint Foundation is a great option for running web sites of all kinds – not just team sites. It is a great option for many reasons, but in reality it is supported by Microsoft, and above all it is FREE (yay!), and it is extremely easy to get started.  From a functionality perspective – it’s hard to beat SharePoint. Even the free version, SharePoint Foundation, offers simple data connectivity (through BCS), cross browser support, accessibility, support for Office Web Apps, blogs, wikis, templates, document support, health analyzer, support for presence, and MUCH more.I often get asked: “Can I use SharePoint 2010 as a document management system?” The answer really depends on ·          What are your specific requirements? ·          What systems you currently have in place for managing documents. ·          And of course how much money you have J Benefits? Not many large organizations have benefited from SharePoint yet. For some it has been an IT project to see what they can achieve with it, for others it has been used as a collaborative platform or in many cases an extended intranet. SharePoint 2010 has changed the game slightly as the improvements that Microsoft have made have been noted by organizations, and we are seeing a lot of companies starting to build specific business applications using SharePoint as the basis, and nearly every business process will require documents at some stage. If you require a document management system and have SharePoint in place then it can be a relatively straight forward decision to use SharePoint, as long as you have reviewed the considerations just discussed. The collaborative nature of SharePoint 2010 is also a massive advantage, as specific departmental or project sites can be created quickly and easily that allow workers to interact in a variety of different ways using one source of information.  This also benefits an organization with regards to how they manage the knowledge that they have, as if all of their information is in one source then it is naturally easier to search and manage. Is SharePoint right for your organization? As just discussed, this can only be determined after defining your requirements and also planning a longer term strategy for how you will manage your documents and information. A key factor to look at is how the users would interact with the system and how much value would it get for your organization. The amount of data and documents that organizations are creating is increasing rapidly each year. Therefore the ability to archive this information, whilst keeping the ability to know what you have and where it is, is vital to any organizations management of their information life cycle. SharePoint is best used for the initial life of business documents where they need to be referenced and accessed after time. It is often beneficial to archive these to overcome for storage and performance issues. FREE CMS – SharePoint, Really? In order to show some of the completely of what comes with this free version of SharePoint 2010, I thought it would make sense to use Wikipedia (since every one trusts it as a credible source). Wikipedia shows that a web content management system typically has the following components: Document Management:   -       CMS software may provide a means of managing the life cycle of a document from initial creation time, through revisions, publication, archive, and document destruction. SharePoint is king when it comes to document management.  Version history, exclusive check-out, security, publication, workflow, and so much more.  Content Virtualization:   -       CMS software may provide a means of allowing each user to work within a virtual copy of the entire Web site, document set, and/or code base. This enables changes to multiple interdependent resources to be viewed and/or executed in-context prior to submission. Through the use of versioning, each content manager can preview, publish, and roll-back content of pages, wiki entries, blog posts, documents, or any other type of content stored in SharePoint.  The idea of each user having an entire copy of the website virtualized is a bit odd to me – not sure why anyone would need that for anything but the simplest of websites. Automated Templates:   -       Create standard output templates that can be automatically applied to new and existing content, allowing the appearance of all content to be changed from one central place. Through the use of Master Pages and Themes, SharePoint provides the ability to change the entire look and feel of site.  Of course, the older brother version of SharePoint – SharePoint Server 2010 – also introduces the concept of Page Layouts which allows page template level customization and even switching the layout of an individual page using different page templates.  I think many organizations really think they want this but rarely end up using this bit of functionality.  Easy Edits:   -       Once content is separated from the visual presentation of a site, it usually becomes much easier and quicker to edit and manipulate. Most WCMS software includes WYSIWYG editing tools allowing non-technical individuals to create and edit content. This is probably easier described with a screen cap of a vanilla SharePoint Foundation page in edit mode.  Notice the page editing toolbar, the multiple layout options…  It’s actually easier to use than Microsoft Word. Workflow management: -       Workflow is the process of creating cycles of sequential and parallel tasks that must be accomplished in the CMS. For example, a content creator can submit a story, but it is not published until the copy editor cleans it up and the editor-in-chief approves it. Workflow, it’s in there. In fact, the same workflow engine is running under SharePoint Foundation that is running under the other versions of SharePoint.  The primary difference is that with SharePoint Foundation – you need to configure the workflows yourself.   Web Standards: -       Active WCMS software usually receives regular updates that include new feature sets and keep the system up to current web standards. SharePoint is in the fourth major iteration under Microsoft with the 2010 release.  In addition to the innovation that Microsoft continuously adds, you have the entire global ecosystem available. Scalable Expansion:   -       Available in most modern WCMSs is the ability to expand a single implementation (one installation on one server) across multiple domains. SharePoint Foundation can run multiple sites using multiple URLs on a single server install.  Even more powerful, SharePoint Foundation is scalable and can be part of a multi-server farm to ensure that it will handle any amount of traffic that can be thrown at it. Delegation & Security:  -       Some CMS software allows for various user groups to have limited privileges over specific content on the website, spreading out the responsibility of content management. SharePoint Foundation provides very granular security capabilities. Read @ http://msdn.microsoft.com/en-us/library/ee537811.aspx Content Syndication:  -       CMS software often assists in content distribution by generating RSS and Atom data feeds to other systems. They may also e-mail users when updates are available as part of the workflow process. SharePoint Foundation nails it.  With RSS syndication and email alerts available out of the box, content syndication is already in the platform. Multilingual Support: -       Ability to display content in multiple languages. SharePoint Foundation 2010 supports more than 40 languages. Read More Read more @ http://msdn.microsoft.com/en-us/library/dd776256(v=office.12).aspxYou can download the free version from http://www.microsoft.com/en-us/download/details.aspx?id=5970

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  • Free ebook: Programming Windows 8 Apps with HTML, CSS, and JavaScript

    - by TATWORTH
    Originally posted on: http://geekswithblogs.net/TATWORTH/archive/2013/11/03/free-ebook-programming-windows-8-apps-with-html-css-and.aspxAt http://blogs.msdn.com/b/microsoft_press/archive/2012/10/29/free-ebook-programming-windows-8-apps-with-html-css-and-javascript.aspx, there is a free E-Book: Programming Windows 8 Apps with HTML, CSS, and JavaScript. "This free E-book provides comprehensive coverage of the platform for Windows Store apps."

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