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• Why is thread local storage so slow?

  - by dsimcha

  I'm working on a custom mark-release style memory allocator for the D programming language that works by allocating from thread-local regions. It seems that the thread local storage bottleneck is causing a huge (~50%) slowdown in allocating memory from these regions compared to an otherwise identical single threaded version of the code, even after designing my code to have only one TLS lookup per allocation/deallocation. This is based on allocating/freeing memory a large number of times in a loop, and I'm trying to figure out if it's an artifact of my benchmarking method. My understanding is that thread local storage should basically just involve accessing something through an extra layer of indirection, similar to accessing a variable via a pointer. Is this incorrect? How much overhead does thread-local storage typically have? Note: Although I mention D, I'm also interested in general answers that aren't specific to D, since D's implementation of thread-local storage will likely improve if it is slower than the best implementations.

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• Concurrency Violation in NHibernate( c#) example

  - by vijaysylvester

  For quite some time , I was reading about the optimistic concurrency in NHibernate. If what i understood was correct then the below sample should hold good. Consider two transactions T1 and T2. When T1 and T2 are done simultaneously , the state(DB entries) gets updated with the values of the most latest update.(T1 or T2). Though it seems to be conceptually sound , how do i simulate this for the purpose of understanding and integration testing.? Can someone help me with a sample c# code.? Thanks , vijay

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• Problems with MVC Ajax.ActionLink and returning a PartialView

  - by mwright

  I'm trying to implement a simple Ajax update using MVC and have run into an issue. My understanding of how to implement Ajax with MVC is to use an Ajax.ActionLink which allows the content to be updated based on user interaction. I have an Ajax.ActionLink that looks like the following: <%= Ajax.ActionLink("Call Ajax", "Ajax", new AjaxOptions{UpdateTargetId = "updateDiv"}) %> If, in the controller, I return a string it works fine. However, when returning a PartialView instead, nothing happens. I can step through and verify that the controller is "returning" the partial view but nothing shows up in what I'm calling the updateDiv. How can I go about determining what the problem is?

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• How does delete deal with pointer constness?

  - by aJ

  I was reading this question Deleting a const pointer and wanted to know more about delete behavior. Now, as per my understanding: delete expression works in two steps: invoke destructor then releases the memory (often with a call to free()) by calling operator delete. operator delete accepts a void*. As part of a test program I overloaded operator delete and found that operator delete doesn't accept const pointer. Since operator delete does not accept const pointer and delete internally calls operator delete, how does Deleting a const pointer work ? Does delete uses const_cast internally?

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• What is node.js?

  - by Jeffrey

  I don't fully get what node.js is all about. Maybe it's because I am mainly a web based business app developer. Can someone please explain what it is and the use of it? Thanks. My understanding so far is that: The programming model is event driven, especially the way it handles IO. It uses javascript and the parser is V8. It can be easily used to create concurrent server apps. Are my understandings correct? If yes, then what are the benefits of evented IO, is it just more for the concurrency stuffs? Also is the direction of node.js to become a framework like, javascript based (v8 based) programming model?

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• MIT vs. BSD vs. Dual License

  - by ryanve

  My understanding is that: MIT-licensed projects can be used/redistributed in BSD-licensed projects. BSD-licensed projects can be used/redistributed in MIT-licensed projects. The MIT and the BSD 2-clause licenses are essentially identical. BSD 3-clause = BSD 2-clause + the "no endorsement" clause Issuing a dual license allows users to choose from those licenses—not be bound to both. If all of the above is correct, then what is the point of using a dual MIT/BSD license? Even if the BSD refers to the 3-clause version, then can't a user legally choose to only abide by the MIT license? It seems that if you really want the "no endorsement" clause to apply then you have to license it as just BSD (not dual). If you don't care about the "no endorsement" clause, then MIT alone is sufficient and MIT/BSD is redundant. Similarly, since the MIT and BSD licenses are both "GPL-compatible" and can be redistributed in GPL-licensed projects, then dual licensing MIT/GPL also seems redundant.

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• fsutil hardlink doesn't work?

  - by Alix Axel

  I was looking for a way to create hard links under Windows and I found this page: http://technet.microsoft.com/en-us/library/cc788097.aspx To try it out, I created a file (1.txt) on the root of my C: drive with 100 lines of the following content: C:\1.txt (2.598 bytes): test test test test test Then I open the command prompt and type: fsutil hardlink create C:\2.txt C:\1.txt Success, 2.txt was created but when I go to see it's size it has exactly 2.598 bytes and also noticed some strange behaviours (as far as my understanding of hard links goes): If I delete 2.txt (the hard linked file) 1.txt is not deleted, and vice-versa. If I open 2.txt after I delete 1.txt (the original file) the content is still the same. How does the fsutil hardlink create command differs from the copy command? And how can I create a true hard link under Windows? I'm using Windows XP SP 3, and my file system is NTFS.

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• How to implement a graph-structured stack?

  - by Emil

  Ok, so I would like to make a GLR parser generator. I know there exist such programs better than what I will probably make, but I am doing this for fun/learning so that's not important. I have been reading about GLR parsing and I think I have a decent high level understanding of it now. But now it's time to get down to business. The graph-structured stack (GSS) is the key data structure for use in GLR parsers. Conceptually I know how GSS works, but none of the sources I looked at so far explain how to implement GSS. I don't even have an authoritative list of operations to support. Can someone point me to some good sample code/tutorial for GSS? Google didn't help so far. I hope this question is not too vague.

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• D3.js binding an object to data and appending for each key

  - by frshca

  I'm a D3.js newbie and I'm learning how to play around with data. Let's say I have an object with names as keys, and each key has an array of numbers like this: var userdata = { 'John' : [0, 1, 3, 9, 8, 7], 'Harry': [0, 10, 7, 1, 1, 11], 'Steve': [3, 1, 4, 4, 4, 17], 'Adam' : [4, 77, 2, 13, 11, 13] }; For each user, I would like to append an SVG object and then plot the line with the array of values for that user. So here is my assumption of how that would look based on tutorials, but I know it is incorrect. This is to show my limited knowledge and give better understanding of what I'm doing: First I should create the line var line = d3.svg.line().interpolate('basis'); Then I want to bind the data to my body and append an svg element for each key: d3.select('body') .selectAll('svg') .data(userdata) .enter() .append('svg') .append(line) .x(function(d, i) { return i; }) .y(function(d) { return d[i]; }); So am I close??

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• Zipping Rx IObservable with infinite number set

  - by Toni Kielo

  I have a IObservable [named rows in the sample below] from Reactive extensions framework and I want to add index numbers to each object it observes. I've tried to implement this using Zip function: rows.Zip(Enumerable.Range(1, int.MaxValue), (row, index) => new { Row = row, Index = index }) .Subscribe(a => ProcessRow(a.Row, a.Index), () => Completed()); .. but unfortunately this throws ArgumentOutOfRangeException: Specified argument was out of the range of valid values. Parameter name: disposables Am I understanding the Zip function wrong or is there a problem with my code? The Range part of the code doesn't seem to be the problem and the IObservable isn't yet receiving any events.

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• What learning habits can you suggest?

  - by Asaf R

  Hi, Our profession often requires deep learning; sitting down and reading, and understanding. I'm currently undergoing an exam period, and I'm looking for ways to learn more effectively. I'm not asking about what to learn, or whether to prefer blogs over books, etc. My question is much more physical than that - What do you do when need to study, and I mean study hard? I'm looking for answers such as I slice my time to 2.5 hours intervals and make a break between them, but never during. I keep a jar of water nearby. I wake up at 6 o'clock sharp and start my day with a session at the gym. What good learning habits did acquire, or wish you had acquired? (I know this isn't strictly programming related, but it is programmers related)

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• Why is ruby called a dsl?

  - by b_ayan

  Recently, when I tried to explain why Ruby is a DSL to an intern at my organisation, I was not able to articulate my reasonings to the effect I would like to. Maybe I do not understand the space well enough to teach the nuances. Redirecting him to Martin Fowler' article or the google ranked one InfoQ or other material has not helped much either. Can some explain why Ruby is a DSL with an example / parallel situation which is not voodoo stuff for someone who is fairly new to the world of code? Understanding the ideology might also help in elaborating the intricacies of the rails ecosystem?

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• Sybase IQ: How to create a DBSPACE with raw device?

  - by Martin Klier

  I try to add a dbspace to a demo database, using a raw device on Linux. I always get SQL error 1010000, file already exists: CREATE DBSPACE KLMTEST USING FILE DF1 '/dev/disk/by-id/scsi-1HITACHI_730109670008' IQ STORE; Could not execute statement. The file '/dev/disk/by-id/scsi-1HITACHI_730109670008' already exists. -- (st_database.cxx 2215) SQLCODE=-1010000, ODBC 3 State="HY000" Line 1, column 1 For my understanding, the raw device has to exist BEFORE the Db can use it. How can I specify the raw device's name in order to make the command work? Permissions of the device are 770 for the sybase user. Thanks a lot Martin

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• mysql, sqlite database source code

  - by Yang

  hi guys, i know implementing database is a huge topic, but i want to have a basic understanding of how database systems works (e.g. memory management, binary tree, transaction, sql parsing, multi-threading, partitions, etc) by investigating the source code of the database, since there are a few already proven very robust open source databases like mysql, sqlite and so on. however, the code are very complicated and i have no clue where to start. also i find that the old school database textbooks are only explaining the theory, not the implementation details. Can anyone suggest how should i get started and is there any books that emphasis on the technology and techniques of building dbms used in modern database industry? Thank in advance!

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• How to style an asp.net menu with CSS

  - by md1337

  I'm in the process of styling an asp.net menu and I'm trying to understand the meaning of the StaticSelectedStyle-CssClass and StaticHoverStyle-CssClass parameters. My understanding is that the styles defined with these parameters are applied as CSS classes to the relevant elements, whenever needed. So I created my menu as follows: <asp:Menu ID="NavigationMenu" DataSourceID="NavigationSiteMapDataSource" StaticMenuStyle-CssClass="StaticMenuStyle" StaticMenuItemStyle-CssClass="StaticMenuItemStyle" StaticSelectedStyle-CssClass="StaticSelectedStyle" StaticHoverStyle-CssClass="StaticHoverStyle" Orientation="Horizontal" MaximumDynamicDisplayLevels="0" runat="server"> </asp:Menu> It works for StaticMenuStyle-CssClass and StaticMenuStyle-CssClass (the classes are applied to the relevant elements), but StaticSelectedStyle-CssClass and StaticHoverStyle-CssClass are not applied, regardless of the selected or hover status of an element. What am I supposed to do to make this work? Thanks.

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• How to recognize touch events and control a script object inside UIWebView?

  - by Markus S.

  Situation: I have an UIView with an UIWebView in it. When the viewDidLoad the Javascript Object inside the UIWebView is called (Microsoft Seadragon AJAX JS). For your Understanding: Seadragon loads a specified megapixel image(JPEG) and in a Desktop Browser like Firefox i can Zoom into the image and I can drag the crop for example from the middle to the left. In the iPhone Simulator (for iPad) only the Zooming Function is working on one single tap but when i try to drag the crop (with left mouse button click and holding it) I'm dragging the whole UIWebView but not the crop of course! Is that feature which the simulator isn't able to handle or what's yout solutin guys? Special Thanks!! P.S.: It's a bit jiggling when the zooming function of Seadragon is called. Is that authentic to the real performance of the iPad or does the simulator not have the power as the iPad has?

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• BFS traversal of directed graph from a given node

  - by p1

  Hi, My understanding of basic BFS traversal for a graph is: BFS { Start from any node . Add it to que. Add it to visited array While(que is not empty) { remove head from queue. Print node; add all unvisited direct subchilds to que; mark them as visited } } However, if we have to traverse a DIRECTED graph from a given node and not all nodes are accessible from the given node [directly or indirectly] how do we use BFS for the same. Can you please explain in this graph as well: a= b = d = e = d a= c = d Here if the starting node is b , we never print a and c. Am I missing something in the algorithm. P.S: I used "HashMap adj = new HashMap();" to create the adjacencey list to store graph Any pointers are greatly appreciated. Thanks.

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• What are Windows code pages?

  - by Mike D

  I'm trying to gain a basic understanding of what is meant by a Windows code page. I kind of get the feeling it's a translation between a given 8 bit value and some 'abstraction' for a given character graphic. I made the following experiment. I created a "" character literal with two versions of the letter u with an umlaut. One created using the ALT 129 (uses code page 437) value and one using the ALT 0252 (uses code page 1252) value. When I examined the literal both characters had the value 252. Is 252 the universal 8 bit abstraction for u with an umlaut? Is it the Unicode value? Aside from keyboard input are there any library routines or system calls that use code pages? For example is there a function to translate a string using a given code table (as above for the ALT 129 value)?

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• C# WCF/WebService: Interoperable exception handling.

  - by michael paul

  I understand that WCF will convert an exception into a fault and send it back as a SOAP message, but I was wondering if this is truly interoperable. I guess I'm having a tough time trying to figure out this possible scenario: Client (Java) calls a WCF Service (LoginService). Server checks for proper authorization, user authorization fails. Server throws an UnauthorizedAccessException. WCF converts this into a Fault somehow. (* - See Below As Well) Client has to be able to know how to read this Fault. I guess I'm just having a tough time understanding how this could still be interoperable because it is expecting Java to know how to translate a SOAP Fault that .NET encodes from an UnauthorizedAccessException. Also, how does .NET actually convert the exception to a fault, what goes in as the fault code, name, etc. Some of the things seem to be "duh"s like perhaps the Fault Name is "UnauthorizedAccessException", but I'd rather know for sure than guess.

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• The advantages and disadvantages of using ORM

  - by JHarley1

  Good Morning, I would like to discuss today the advantages and disadvantages of using ORM (such as ADO.NET). Advantages: Speeds-up Development - eliminates the need for repetitive SQL code. Reduces Development Time. Reduces Development Costs. Overcomes vendor specific SQL differences - the ORM knows how to write vendor specific SQL so you don't have to. Disadvantages: Loss in developer productivity whilst they learn to program with ORM. Developers loose understanding of what the code is actually doing - the developer is more in control using SQL. ORM has a tendency to be slow. ORM fail to compete against SQL queries for complex queries. In summary, I believe that the disadvantages of using an ORM (mainly the reduced time taken to perform repetitive tasks) is far outweighed by the disadvantages of ORM e.g. its difficulty to get to grips with. Can people point out were I am going wrong and suggest any further advantages/disadvantages. Many Thanks, J

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• SPWeb.Webs, Site vs SubSite

  - by noob.spt

  Hi, I have a very basic question here. I am confused between SPSite. SiteCollection and SPWeb. So my understanding is (or what I could research on this) that, http://My_server TOP Level SIte or SPWEbApplication http://My_server/My_site Site Collection or SPSite Now a site under SPSite that will be referenced through SPWeb. So what are we getting when using SPWeb.Webs. What is a Subsite? Please let me know if I need to rephrase the question or more info is needed. Thanks. SPWeb mySite = SPContext.Current.Web; SPWebCollection sites = mySite.Webs; foreach (SPWeb subSite in sites) { Response.Write(SPEncode.HtmlEncode(subSite.Title) + "<BR>"); }

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• Is `hg pull --rebase` analogous to `svn update`?

  - by allyourcode

  This question assumes there's a "blessed" central repository that members of a team clone from push to when they have contributions that they want other team members to see pull from when they want to see other people's contributions. etc. If so, I would assume hg update is not analogous to svn update (why would there be two commands that do exactly the same thing?). From what I can gather, hg update more like svn revert. Is that correct? Update: My understanding of rebase is largely based on the "A common case" section on this page: http://mercurial.selenic.com/wiki/RebaseProject

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• How to use RTPSocket to send RTP packets

  - by Afro Genius

  Hi there, am relatively new to JMF but have gone through the documents and have a sufficient understanding of how it works. That been said am having some trouble implementing a the server side for RTPSockets. After looking at their illustrations and example. I am still abit confused. Am I to develop a datasource and also datasink classes to handle the transfer? What am trying to do is stream data from my application to the underlying network and receive it back through another application. I have and understand receiving but just can't get my head around the steps involved for sending. Any help would be most appreciated.

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• Locking on an object...

  - by Mystere Man

  I often see code like that which is shown here, ie where an object is allocated and then used as a "lock object". It seems to me that you could use any object for this, including the event itself as the lock object. Why allocate a new object that does nothing? My understanding is that calling lock() on an object doesn't actually alter the object itself, nor does it actually lock it from being used, it's simply used as a placeholder for multiple lock statements to anchor on. So my question is, is this really a good thing to do?

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• Computing orientation of a square and displaying an object with the same orientation

  - by Robin

  Hi, I wrote an application which detects a square within an image. To give you a good understanding of how such an image containing such a square, in this case a marker, could look like: What I get, after the detection, are the coordinates of the four corners of my marker. Now I don't know how to display an object on my marker. The object should have the same rotation/angle/direction as the marker. Are there any papers on how to achieve that, any algorithms that I can use that proofed to be pretty solid/working? It doesn't need to be a working solution, it could be a simple description on how to achieve that or something similar. If you point me at a library or something, it should work under linux, windows is not needed but would be great in case I need to port the application at some point. I already looked at the ARToolkit but they you camera parameter files and more complex matrices while I only got the four corner points and a single image instead of a whole video / camera stream.

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